Nest predation is the most important source of reproductive failure for many bird species, thus p... more Nest predation is the most important source of reproductive failure for many bird species, thus placing nests in ‘safe’ locations that minimise predation risk is paramount to maximising fitness. After a nest predation event, some species have been shown to manage the risk of nest predation for subsequent re-nesting attempts by moving to a new location, placing re-nests in areas with increased cover, or changing the height above ground at which the re-nest is placed. The extent to which this is an adaptive behaviour for birds in general is not yet clear, as existing studies are almost exclusively restricted to northern hemisphere species and species that do not breed cooperatively. Here, we examined the re-nesting behaviour of Bell Miners (Manorina melanophrys), a species of honeyeater endemic to Australia that is both multi-brooded and also frequently re-nests soon after nesting failure; females can build up to five nests in a breeding season. We tested if these females managed within-season nest predation risk by changing nest site characteristics (height from ground and distance between nests) between successive nesting attempts. We found that female miners did indeed manage predation risk by reducing the height from the ground at which they placed re-nests following predation events, but contrary to our second prediction we found no difference in distances moved to re-nest after females experienced nest predation or successfully rearing young
Tropical and subtropical species typically experience relatively high atmospheric temperatures du... more Tropical and subtropical species typically experience relatively high atmospheric temperatures during reproduction, and are subject to climate-related challenges that are largely unexplored, relative to more extensive work conducted in temperate regions. We studied the effects of high atmospheric and nest temperatures during reproduction in the zebra finch. We characterized the temperature within nests in a subtropical population of this species in relation to atmospheric temperature. Temperatures within nests frequently exceeded the level at which embryo's develop optimally, even in the absence of parental incubation. We experimentally manipulated internal nest temperature to demonstrate that an average difference of 6°C in the nest temperature during the laying period reduced hatching time by an average of 3% of the total incubation time, owing to 'ambient incubation'. Given the avian constraint of laying a single egg per day, the first eggs of a clutch are subject to prolonged effects of nest temperature relative to later laid eggs, potentially increasing hatching asynchrony. While birds may ameliorate the negative effects of ambient incubation on embryonic development by varying the location and design of their nests, high atmospheric temperatures are likely to constitute an important selective force on avian reproductive behaviour and physiology in subtropical and tropical regions, particularly in the light of predicted climate change that in many areas is leading to a higher frequency of hot days during the periods when birds breed.
Despite important differences between infectious diseases and cancers, tumour development (neopla... more Despite important differences between infectious diseases and cancers, tumour development (neoplasia) can nonetheless be closely compared to infectious disease because of the similarity of their effects on the body. On this basis, we predict that many of the life-history (LH) responses observed in the context of host-parasite interactions should also be relevant in the context of cancer. Parasites are thought to affect LH traits of their hosts because of strong selective pressures like direct and indirect mortality effects favouring, for example, early maturation and reproduction. Cancer can similarly also affect LH traits by imposing direct costs and/or indirectly by triggering plastic adjustments and evolutionary responses. Here, we discuss how and why a LH focus is a potentially productive but under-exploited research direction for cancer research, by focusing our attention on similarities between infectious disease and cancer with respect to their effects on LH traits and their evolution. We raise the possibility that LH adjustments can occur in response to cancer via maternal/paternal effects and that these changes can be heritable to (adaptively) modify the LH traits of their offspring. We conclude that LH adjustments can potentially influence the transgenerational persistence of inherited oncogenic mutations in populations.
Understanding Avian Influenza Virus (AIV) infection dynamics in wildlife is crucial because of po... more Understanding Avian Influenza Virus (AIV) infection dynamics in wildlife is crucial because of possible virus spill over to livestock and humans. Studies from the northern hemisphere have suggested several ecological and environmental drivers of AIV prevalence in wild birds. To determine if the same drivers apply in the southern hemisphere, where more irregular environmental conditions prevail, we investigated AIV prevalence in ducks in relation to biotic and abiotic factors in south-eastern Australia. We sampled duck faeces for AIV and tested for an effect of bird numbers, rainfall anomaly, temperature anomaly and long-term ENSO (El-Niño Southern Oscillation) patterns on AIV prevalence. We demonstrate a positive long term effect of ENSO-related rainfall on AIV prevalence. We also found a more immediate response to rainfall where AIV prevalence was positively related to rainfall in the preceding 3-7 months. Additionally, for one duck species we found a positive relationship between ...
The question about whether evolution is unpredictable and stochastic or intermittently constraine... more The question about whether evolution is unpredictable and stochastic or intermittently constrained along predictable pathways is the subject of a fundamental debate in biology, in which understanding convergent evolution plays a central role. At the molecular level, documented examples of convergence are rare and limited to occurring within specific taxonomic groups. Here we provide evidence of constrained convergent molecular evolution across the metazoan tree of life. We show that resistance to toxic cardiac glycosides produced by plants and bufonid toads is mediated by similar molecular changes to the sodium-potassium-pump (Na+/K+-ATPase) in insects, amphibians, reptiles, and mammals. In toadfeeding reptiles, resistance is conferred by two point mutations that have evolved convergently on four occasions, whereas evidence of a molecular reversal back to the susceptible state in varanid lizards migrating to toad-free areas suggests that toxin resistance is maladaptive in the absence of selection. Importantly, resistance in all taxa is mediated by replacements of 2 of the 12 amino acids comprising the Na+/K+-ATPase H1–H2 extracellular domain that constitutes a core part of the cardiac glycoside binding site. We provide mechanistic insight into the basis of resistance by showing that these alterations perturb the interaction between the cardiac glycoside bufalin and the Na+/K+-ATPase. Thus, similar selection pressures have resulted in convergent evolution of the same molecular solution across the breadth of the animal kingdom, demonstrating how a scarcity of possible solutions to a selective challenge can lead to highly predictable evolutionary responses.
Intraspecific killing without cannibalism
is rare in birds. I report an observation of an
adult P... more Intraspecific killing without cannibalism is rare in birds. I report an observation of an adult Pacific Reef Egret (Egretta sacra) killing an adult conspecific at One Tree Island, Great Barrier Reef, Australia. The motivation and context for the killing were not apparent. To the best of my knowledge, this is the first report of intraspecific killing in Pacific Reef Egrets.
Invasive species can induce shifts in habitat use by native taxa: either by modifying habitat ava... more Invasive species can induce shifts in habitat use by native taxa: either by modifying habitat availability, or by repelling or attracting native species to the vicinity of the invader. The ongoing invasion of cane toads (Rhinella marina) through tropical Australia might affect native frogs by affecting refuge-site availability, because both frogs and toads frequently shelter by day in burrows. Our laboratory and field studies in the wet-dry tropics show that native frogs of at least three species (Litoria tornieri, Litoria nasuta and Litoria dahlii) preferentially aggregate with conspecifics, and with (some) other species of native frogs. However, the frogs rarely aggregated with cane toads either in outdoor arenas or in standardized experimental burrows that we monitored in the field. The native frogs that we tested either avoided burrows containing cane toads (or cane toad scent) or else ignored the stimulus (i.e. treated such a burrow in the same way as they did an empty burrow). Native frogs selected a highly non-random suite of burrows as diurnal retreat sites, whereas cane toads were less selective. Hence, even in the absence of toads, frogs do not use many of the burrows that are suitable for toads. The invasion of cane toads through tropical Australia is unlikely to have had a major impact on retreat-site availability for native frogs.
Fish are frequently considered the top predator in freshwater food web models despite evidence th... more Fish are frequently considered the top predator in freshwater food web models despite evidence that predatory birds can impact fish populations. In this study, we quantified bird predation rates on experimental populations of rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)) created by stocking nine small lakes in British Columbia, Canada. Combining estimates of fish mortality with estimated bird predation rates allowed us to partition fish mortality into that due to birds versus cannibalism. Our results indicated that bird predators had significant impacts on age-1 trout populations, but little impact on age-0 trout. Common loons (Gavia immer Brunnich, 1764) were the principle predator among eight predatory bird species present, apparently consuming nearly 50% of all stocked age-1 trout and explaining almost 50% of variation in mortality rates. Age-1 trout mortality did not differ significantly from zero in lakes without loons. Birds consumed a small proportion of age-0 trout, and estimated consumption explained none of the variation in age-0 trout mortality among lakes. We conclude that birds affect fish populations by asymmetric predation on different age (size) classes and can be important top predators that should not be ignored when characterizing freshwater food webs in lakes.
Consistent individual differences in behaviour, termed personality, are common in animal populati... more Consistent individual differences in behaviour, termed personality, are common in animal populations and can constrain their responses to ecological and environmental variation, such as temperature. Here, we show for the first time that normal within-daytime fluctuations in temperature of less than 38C have large effects on personality for two species of juvenile coral reef fish in both observational and manipulative experiments. On average, individual scores on three personality traits (PTs), activity, boldness and aggressiveness, increased from 2.5- to sixfold as a function of temperature. However, whereas most individuals became more active, aggressive and bold across temperature contexts (were plastic), others did not; this changed the individual rank order across temperatures and thus altered personality. In addition, correlations between PTs were consistent across temperature contexts, e.g. fish that were active at a given temperature also tended to be both bold and aggressive. These results (i) highlight the importance of very carefully controlling for temperature when studying behavioural variation among and within individuals and (ii) suggest that individual differences in energy metabolism may contribute to animal personality, given that temperature has large direct effects on metabolic rates in ectotherms.
Invasive species can disrupt the communication systems
that native biota use for reproductive int... more Invasive species can disrupt the communication systems that native biota use for reproductive interactions. In tropical Australia, invasive cane toads (Rhinella marina) breed in many of the samewaterbodies that are used by native frogs, and males of both the invader and the native taxa rely on vocal signals to attract mates. We conducted playback experiments to test the hypothesis that calls of toads may influence the calling behaviour of frogs (Limnodynastes convexiusculus and Litoria rothii). Male L. convexiusculus adjusted their calling rate and the variance in inter-call interval in response to a variety of sounds, including the calls of cane toads as well as those of other native frog species, and other anthropogenic noise, whereas L. rothii did not. Within the stimulus periods of playbacks, male L. convexiusculus called more intensely during long silent gaps than during calling blocks. Thus, males of one frog species reduced their calling rate, possibly to minimise energy expenditure during periods of acoustic interference generated by cane toads. In spite of such modifications, the number of overlapping calls (within stimulus periods) did not differ significantly from that expected by chance. In natural conditions, the calls of cane toads are continuous rather than episodic, leaving fewer gaps of silence that male frogs could exploit. Future work could usefully quantify the magnitude of temporal (e.g. diel and seasonal) and spatial overlap between calling by toads and by frogs and the impact of call-structure shifts on the ability of male frogs to attract receptive females.
Although the invasive Cane Toad’s diet in Australia consists primarily of insects, vertebrates ar... more Although the invasive Cane Toad’s diet in Australia consists primarily of insects, vertebrates are occasionally ingested. Herein we report on predation by the Cane Toad on a nestling bird.
Cane Toads (Rhinella marina; hereafter ‘toads’) are large, toxic American anurans that were intro... more Cane Toads (Rhinella marina; hereafter ‘toads’) are large, toxic American anurans that were introduced to Australia in 1935. Research on their ecological impact has focussed on the lethal ingestion of toxic toads by native frog-eating predators. Less attention has been paid to the potential impacts of Cane Toads as predators, although these large anurans sometimes eat vertebrates, such as nestling birds and bird eggs. We review published and unpublished data on interactions between Cane Toads and Australian ground-nesting birds, and collate distributional and breeding information to identify the avian taxa potentially at risk of having eggs or chicks eaten by Cane Toads. Cane Toads are currently sympatric with 80 ground-nesting bird species in Australia, andfive additional species of bird occur within the predicted future range of the toad. Although many species of bird are potentially at risk, available data suggest there is minimal impact of Cane Toads on ground-nesting species. Future research could usefully address both direct and indirect impacts of the invasion by Cane Toads, ideally with detailedfield observations of these impacts on nesting success and of changes in bird breeding success as a function of invasion by toads.
Road-killed animals are easy and inexpensive to survey, and may provide information about
species... more Road-killed animals are easy and inexpensive to survey, and may provide information about species distributions, abundances, and mortality rates. As with any sampling method, however, we need to explore methodological biases in such data. First, how does an animal’s behavior (e.g., use of the center vs. periphery of the road) influence its vulnerability to vehicular traffic? Second, how rapidly do post-mortem processes (scavenging by other animals, destruction or displacement by subsequent vehicles) change the numbers and locations of roadkills? Our surveys of anurans on a highway in tropical Australia show that different anuran species are distributed in different ways across the width of the road, and that locations of live versus dead animals sometimes differ within a species. Experimental trials show that location on the road affects the probability of being hit by a vehicle, with anurans in the middle of the road begin hit 35% more often than anurans on the edges; thus, center-using species aremore likely to be hit than edge-using taxa. The magnitude of post-mortem displacement and destruction by subsequent vehicles depended on anuran species and body size. The mean parallel displacement distance was 122.7 cm, and carcasses of thin-skinned species exhibited greater post-mortem destruction. Scavenging raptors removed 73% of carcasses, most within a few hours of sunrise. Removal rates were biased with respect to size and species. Overall, our studies suggest that investigators should carefully evaluate potential biases before using roadkill counts to estimate underlying animal abundances or mortality rates.
The impact of invasive predators on
native prey has attracted considerable scientific
attention, ... more The impact of invasive predators on native prey has attracted considerable scientific attention, whereas the reverse situation (invasive species being eaten by native predators) has been less frequently studied. Such interactions might affect invasion success; an invader that is readily consumed by native species may be less likely to flourish in its new range than one that is ignored by those taxa. Invasive cane toads (Rhinella marina) in Australia have fatally poisoned many native predators (e.g., marsupials, crocodiles, lizards) that attempt to ingest the toxic anurans, but birds are more resistant to toad toxins. We quantified prey preferences of four species of wading birds (Nankeen night heron, purple swamphen, pied heron, little egret) in the wild, by offering cane toads and alternative native prey items (total of 279 trays offered, 14 different combinations of prey types). All bird species tested preferred the native prey, avoiding both tadpole and metamorph cane toads. Avoidance of toads was strong enough to reduce foraging on native prey presented in combination with the toads, suggesting that the presence of cane toads could affect predator foraging tactics, and reduce the intensity of predation on native prey species found in association with toads.
Although interest in the ecological
impacts of invasive species has largely focused on
negative e... more Although interest in the ecological impacts of invasive species has largely focused on negative effects, some native taxa may benefit from invader arrival. In tropical Australia, invasive cane toads (Bufo marinus) have fatally poisoned many native predators (e.g., marsupials, crocodiles, lizards) that attempt to ingest the toxic anurans, but birds appear to be more resistant to toad toxins. We quantified offtake of dead (road-killed) cane toads by raptors (black kites (Milvus migrans) and whistling kites (Haliastur sphenurus)) at a site near Darwin, in the Australian wet-dry tropics. Raptors readily took dead toads, especially small ones, although native frogs were preferred to toads if available. More carcasses were removed in the dry season than the wet season, perhaps reflecting seasonal availability of alternative prey. Raptors appeared to recognize and avoid bufotoxins, and typically removed and consumed only the toads’ tongues (thereby minimizing toxin uptake). The invasion of cane toads thus constitutes a novel prey type for scavenging raptors, rather than (as is the case for many other native predators) a threat to population viability.
Nest predation is the most important source of reproductive failure for many bird species, thus p... more Nest predation is the most important source of reproductive failure for many bird species, thus placing nests in ‘safe’ locations that minimise predation risk is paramount to maximising fitness. After a nest predation event, some species have been shown to manage the risk of nest predation for subsequent re-nesting attempts by moving to a new location, placing re-nests in areas with increased cover, or changing the height above ground at which the re-nest is placed. The extent to which this is an adaptive behaviour for birds in general is not yet clear, as existing studies are almost exclusively restricted to northern hemisphere species and species that do not breed cooperatively. Here, we examined the re-nesting behaviour of Bell Miners (Manorina melanophrys), a species of honeyeater endemic to Australia that is both multi-brooded and also frequently re-nests soon after nesting failure; females can build up to five nests in a breeding season. We tested if these females managed within-season nest predation risk by changing nest site characteristics (height from ground and distance between nests) between successive nesting attempts. We found that female miners did indeed manage predation risk by reducing the height from the ground at which they placed re-nests following predation events, but contrary to our second prediction we found no difference in distances moved to re-nest after females experienced nest predation or successfully rearing young
Tropical and subtropical species typically experience relatively high atmospheric temperatures du... more Tropical and subtropical species typically experience relatively high atmospheric temperatures during reproduction, and are subject to climate-related challenges that are largely unexplored, relative to more extensive work conducted in temperate regions. We studied the effects of high atmospheric and nest temperatures during reproduction in the zebra finch. We characterized the temperature within nests in a subtropical population of this species in relation to atmospheric temperature. Temperatures within nests frequently exceeded the level at which embryo's develop optimally, even in the absence of parental incubation. We experimentally manipulated internal nest temperature to demonstrate that an average difference of 6°C in the nest temperature during the laying period reduced hatching time by an average of 3% of the total incubation time, owing to 'ambient incubation'. Given the avian constraint of laying a single egg per day, the first eggs of a clutch are subject to prolonged effects of nest temperature relative to later laid eggs, potentially increasing hatching asynchrony. While birds may ameliorate the negative effects of ambient incubation on embryonic development by varying the location and design of their nests, high atmospheric temperatures are likely to constitute an important selective force on avian reproductive behaviour and physiology in subtropical and tropical regions, particularly in the light of predicted climate change that in many areas is leading to a higher frequency of hot days during the periods when birds breed.
Despite important differences between infectious diseases and cancers, tumour development (neopla... more Despite important differences between infectious diseases and cancers, tumour development (neoplasia) can nonetheless be closely compared to infectious disease because of the similarity of their effects on the body. On this basis, we predict that many of the life-history (LH) responses observed in the context of host-parasite interactions should also be relevant in the context of cancer. Parasites are thought to affect LH traits of their hosts because of strong selective pressures like direct and indirect mortality effects favouring, for example, early maturation and reproduction. Cancer can similarly also affect LH traits by imposing direct costs and/or indirectly by triggering plastic adjustments and evolutionary responses. Here, we discuss how and why a LH focus is a potentially productive but under-exploited research direction for cancer research, by focusing our attention on similarities between infectious disease and cancer with respect to their effects on LH traits and their evolution. We raise the possibility that LH adjustments can occur in response to cancer via maternal/paternal effects and that these changes can be heritable to (adaptively) modify the LH traits of their offspring. We conclude that LH adjustments can potentially influence the transgenerational persistence of inherited oncogenic mutations in populations.
Understanding Avian Influenza Virus (AIV) infection dynamics in wildlife is crucial because of po... more Understanding Avian Influenza Virus (AIV) infection dynamics in wildlife is crucial because of possible virus spill over to livestock and humans. Studies from the northern hemisphere have suggested several ecological and environmental drivers of AIV prevalence in wild birds. To determine if the same drivers apply in the southern hemisphere, where more irregular environmental conditions prevail, we investigated AIV prevalence in ducks in relation to biotic and abiotic factors in south-eastern Australia. We sampled duck faeces for AIV and tested for an effect of bird numbers, rainfall anomaly, temperature anomaly and long-term ENSO (El-Niño Southern Oscillation) patterns on AIV prevalence. We demonstrate a positive long term effect of ENSO-related rainfall on AIV prevalence. We also found a more immediate response to rainfall where AIV prevalence was positively related to rainfall in the preceding 3-7 months. Additionally, for one duck species we found a positive relationship between ...
The question about whether evolution is unpredictable and stochastic or intermittently constraine... more The question about whether evolution is unpredictable and stochastic or intermittently constrained along predictable pathways is the subject of a fundamental debate in biology, in which understanding convergent evolution plays a central role. At the molecular level, documented examples of convergence are rare and limited to occurring within specific taxonomic groups. Here we provide evidence of constrained convergent molecular evolution across the metazoan tree of life. We show that resistance to toxic cardiac glycosides produced by plants and bufonid toads is mediated by similar molecular changes to the sodium-potassium-pump (Na+/K+-ATPase) in insects, amphibians, reptiles, and mammals. In toadfeeding reptiles, resistance is conferred by two point mutations that have evolved convergently on four occasions, whereas evidence of a molecular reversal back to the susceptible state in varanid lizards migrating to toad-free areas suggests that toxin resistance is maladaptive in the absence of selection. Importantly, resistance in all taxa is mediated by replacements of 2 of the 12 amino acids comprising the Na+/K+-ATPase H1–H2 extracellular domain that constitutes a core part of the cardiac glycoside binding site. We provide mechanistic insight into the basis of resistance by showing that these alterations perturb the interaction between the cardiac glycoside bufalin and the Na+/K+-ATPase. Thus, similar selection pressures have resulted in convergent evolution of the same molecular solution across the breadth of the animal kingdom, demonstrating how a scarcity of possible solutions to a selective challenge can lead to highly predictable evolutionary responses.
Intraspecific killing without cannibalism
is rare in birds. I report an observation of an
adult P... more Intraspecific killing without cannibalism is rare in birds. I report an observation of an adult Pacific Reef Egret (Egretta sacra) killing an adult conspecific at One Tree Island, Great Barrier Reef, Australia. The motivation and context for the killing were not apparent. To the best of my knowledge, this is the first report of intraspecific killing in Pacific Reef Egrets.
Invasive species can induce shifts in habitat use by native taxa: either by modifying habitat ava... more Invasive species can induce shifts in habitat use by native taxa: either by modifying habitat availability, or by repelling or attracting native species to the vicinity of the invader. The ongoing invasion of cane toads (Rhinella marina) through tropical Australia might affect native frogs by affecting refuge-site availability, because both frogs and toads frequently shelter by day in burrows. Our laboratory and field studies in the wet-dry tropics show that native frogs of at least three species (Litoria tornieri, Litoria nasuta and Litoria dahlii) preferentially aggregate with conspecifics, and with (some) other species of native frogs. However, the frogs rarely aggregated with cane toads either in outdoor arenas or in standardized experimental burrows that we monitored in the field. The native frogs that we tested either avoided burrows containing cane toads (or cane toad scent) or else ignored the stimulus (i.e. treated such a burrow in the same way as they did an empty burrow). Native frogs selected a highly non-random suite of burrows as diurnal retreat sites, whereas cane toads were less selective. Hence, even in the absence of toads, frogs do not use many of the burrows that are suitable for toads. The invasion of cane toads through tropical Australia is unlikely to have had a major impact on retreat-site availability for native frogs.
Fish are frequently considered the top predator in freshwater food web models despite evidence th... more Fish are frequently considered the top predator in freshwater food web models despite evidence that predatory birds can impact fish populations. In this study, we quantified bird predation rates on experimental populations of rainbow trout (Oncorhynchus mykiss (Walbaum, 1792)) created by stocking nine small lakes in British Columbia, Canada. Combining estimates of fish mortality with estimated bird predation rates allowed us to partition fish mortality into that due to birds versus cannibalism. Our results indicated that bird predators had significant impacts on age-1 trout populations, but little impact on age-0 trout. Common loons (Gavia immer Brunnich, 1764) were the principle predator among eight predatory bird species present, apparently consuming nearly 50% of all stocked age-1 trout and explaining almost 50% of variation in mortality rates. Age-1 trout mortality did not differ significantly from zero in lakes without loons. Birds consumed a small proportion of age-0 trout, and estimated consumption explained none of the variation in age-0 trout mortality among lakes. We conclude that birds affect fish populations by asymmetric predation on different age (size) classes and can be important top predators that should not be ignored when characterizing freshwater food webs in lakes.
Consistent individual differences in behaviour, termed personality, are common in animal populati... more Consistent individual differences in behaviour, termed personality, are common in animal populations and can constrain their responses to ecological and environmental variation, such as temperature. Here, we show for the first time that normal within-daytime fluctuations in temperature of less than 38C have large effects on personality for two species of juvenile coral reef fish in both observational and manipulative experiments. On average, individual scores on three personality traits (PTs), activity, boldness and aggressiveness, increased from 2.5- to sixfold as a function of temperature. However, whereas most individuals became more active, aggressive and bold across temperature contexts (were plastic), others did not; this changed the individual rank order across temperatures and thus altered personality. In addition, correlations between PTs were consistent across temperature contexts, e.g. fish that were active at a given temperature also tended to be both bold and aggressive. These results (i) highlight the importance of very carefully controlling for temperature when studying behavioural variation among and within individuals and (ii) suggest that individual differences in energy metabolism may contribute to animal personality, given that temperature has large direct effects on metabolic rates in ectotherms.
Invasive species can disrupt the communication systems
that native biota use for reproductive int... more Invasive species can disrupt the communication systems that native biota use for reproductive interactions. In tropical Australia, invasive cane toads (Rhinella marina) breed in many of the samewaterbodies that are used by native frogs, and males of both the invader and the native taxa rely on vocal signals to attract mates. We conducted playback experiments to test the hypothesis that calls of toads may influence the calling behaviour of frogs (Limnodynastes convexiusculus and Litoria rothii). Male L. convexiusculus adjusted their calling rate and the variance in inter-call interval in response to a variety of sounds, including the calls of cane toads as well as those of other native frog species, and other anthropogenic noise, whereas L. rothii did not. Within the stimulus periods of playbacks, male L. convexiusculus called more intensely during long silent gaps than during calling blocks. Thus, males of one frog species reduced their calling rate, possibly to minimise energy expenditure during periods of acoustic interference generated by cane toads. In spite of such modifications, the number of overlapping calls (within stimulus periods) did not differ significantly from that expected by chance. In natural conditions, the calls of cane toads are continuous rather than episodic, leaving fewer gaps of silence that male frogs could exploit. Future work could usefully quantify the magnitude of temporal (e.g. diel and seasonal) and spatial overlap between calling by toads and by frogs and the impact of call-structure shifts on the ability of male frogs to attract receptive females.
Although the invasive Cane Toad’s diet in Australia consists primarily of insects, vertebrates ar... more Although the invasive Cane Toad’s diet in Australia consists primarily of insects, vertebrates are occasionally ingested. Herein we report on predation by the Cane Toad on a nestling bird.
Cane Toads (Rhinella marina; hereafter ‘toads’) are large, toxic American anurans that were intro... more Cane Toads (Rhinella marina; hereafter ‘toads’) are large, toxic American anurans that were introduced to Australia in 1935. Research on their ecological impact has focussed on the lethal ingestion of toxic toads by native frog-eating predators. Less attention has been paid to the potential impacts of Cane Toads as predators, although these large anurans sometimes eat vertebrates, such as nestling birds and bird eggs. We review published and unpublished data on interactions between Cane Toads and Australian ground-nesting birds, and collate distributional and breeding information to identify the avian taxa potentially at risk of having eggs or chicks eaten by Cane Toads. Cane Toads are currently sympatric with 80 ground-nesting bird species in Australia, andfive additional species of bird occur within the predicted future range of the toad. Although many species of bird are potentially at risk, available data suggest there is minimal impact of Cane Toads on ground-nesting species. Future research could usefully address both direct and indirect impacts of the invasion by Cane Toads, ideally with detailedfield observations of these impacts on nesting success and of changes in bird breeding success as a function of invasion by toads.
Road-killed animals are easy and inexpensive to survey, and may provide information about
species... more Road-killed animals are easy and inexpensive to survey, and may provide information about species distributions, abundances, and mortality rates. As with any sampling method, however, we need to explore methodological biases in such data. First, how does an animal’s behavior (e.g., use of the center vs. periphery of the road) influence its vulnerability to vehicular traffic? Second, how rapidly do post-mortem processes (scavenging by other animals, destruction or displacement by subsequent vehicles) change the numbers and locations of roadkills? Our surveys of anurans on a highway in tropical Australia show that different anuran species are distributed in different ways across the width of the road, and that locations of live versus dead animals sometimes differ within a species. Experimental trials show that location on the road affects the probability of being hit by a vehicle, with anurans in the middle of the road begin hit 35% more often than anurans on the edges; thus, center-using species aremore likely to be hit than edge-using taxa. The magnitude of post-mortem displacement and destruction by subsequent vehicles depended on anuran species and body size. The mean parallel displacement distance was 122.7 cm, and carcasses of thin-skinned species exhibited greater post-mortem destruction. Scavenging raptors removed 73% of carcasses, most within a few hours of sunrise. Removal rates were biased with respect to size and species. Overall, our studies suggest that investigators should carefully evaluate potential biases before using roadkill counts to estimate underlying animal abundances or mortality rates.
The impact of invasive predators on
native prey has attracted considerable scientific
attention, ... more The impact of invasive predators on native prey has attracted considerable scientific attention, whereas the reverse situation (invasive species being eaten by native predators) has been less frequently studied. Such interactions might affect invasion success; an invader that is readily consumed by native species may be less likely to flourish in its new range than one that is ignored by those taxa. Invasive cane toads (Rhinella marina) in Australia have fatally poisoned many native predators (e.g., marsupials, crocodiles, lizards) that attempt to ingest the toxic anurans, but birds are more resistant to toad toxins. We quantified prey preferences of four species of wading birds (Nankeen night heron, purple swamphen, pied heron, little egret) in the wild, by offering cane toads and alternative native prey items (total of 279 trays offered, 14 different combinations of prey types). All bird species tested preferred the native prey, avoiding both tadpole and metamorph cane toads. Avoidance of toads was strong enough to reduce foraging on native prey presented in combination with the toads, suggesting that the presence of cane toads could affect predator foraging tactics, and reduce the intensity of predation on native prey species found in association with toads.
Although interest in the ecological
impacts of invasive species has largely focused on
negative e... more Although interest in the ecological impacts of invasive species has largely focused on negative effects, some native taxa may benefit from invader arrival. In tropical Australia, invasive cane toads (Bufo marinus) have fatally poisoned many native predators (e.g., marsupials, crocodiles, lizards) that attempt to ingest the toxic anurans, but birds appear to be more resistant to toad toxins. We quantified offtake of dead (road-killed) cane toads by raptors (black kites (Milvus migrans) and whistling kites (Haliastur sphenurus)) at a site near Darwin, in the Australian wet-dry tropics. Raptors readily took dead toads, especially small ones, although native frogs were preferred to toads if available. More carcasses were removed in the dry season than the wet season, perhaps reflecting seasonal availability of alternative prey. Raptors appeared to recognize and avoid bufotoxins, and typically removed and consumed only the toads’ tongues (thereby minimizing toxin uptake). The invasion of cane toads thus constitutes a novel prey type for scavenging raptors, rather than (as is the case for many other native predators) a threat to population viability.
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have been shown to manage the risk of nest predation for subsequent re-nesting attempts by moving to a new location, placing re-nests in areas with increased cover, or changing the height above ground at which the re-nest is placed. The extent
to which this is an adaptive behaviour for birds in general is not yet clear, as existing studies are almost exclusively restricted to northern hemisphere species and species that do not breed cooperatively. Here, we examined the re-nesting behaviour of
Bell Miners (Manorina melanophrys), a species of honeyeater endemic to Australia that is both multi-brooded and also frequently re-nests soon after nesting failure; females can build up to five nests in a breeding season. We tested if these
females managed within-season nest predation risk by changing nest site characteristics (height from ground and distance between nests) between successive nesting attempts. We found that female miners did indeed manage predation risk by
reducing the height from the ground at which they placed re-nests following predation events, but contrary to our second prediction we found no difference in distances moved to re-nest after females experienced nest predation or successfully
rearing young
is rare in birds. I report an observation of an
adult Pacific Reef Egret (Egretta sacra) killing an
adult conspecific at One Tree Island, Great Barrier
Reef, Australia. The motivation and context for the
killing were not apparent. To the best of my knowledge,
this is the first report of intraspecific killing in
Pacific Reef Egrets.
or by repelling or attracting native species to the vicinity of the invader. The ongoing invasion of cane toads (Rhinella
marina) through tropical Australia might affect native frogs by affecting refuge-site availability, because both frogs
and toads frequently shelter by day in burrows. Our laboratory and field studies in the wet-dry tropics show that
native frogs of at least three species (Litoria tornieri, Litoria nasuta and Litoria dahlii) preferentially aggregate with
conspecifics, and with (some) other species of native frogs. However, the frogs rarely aggregated with cane toads
either in outdoor arenas or in standardized experimental burrows that we monitored in the field. The native frogs
that we tested either avoided burrows containing cane toads (or cane toad scent) or else ignored the stimulus (i.e.
treated such a burrow in the same way as they did an empty burrow). Native frogs selected a highly non-random
suite of burrows as diurnal retreat sites, whereas cane toads were less selective. Hence, even in the absence of toads,
frogs do not use many of the burrows that are suitable for toads. The invasion of cane toads through tropical
Australia is unlikely to have had a major impact on retreat-site availability for native frogs.
in mortality rates. Age-1 trout mortality did not differ significantly from zero in lakes without loons. Birds consumed
a small proportion of age-0 trout, and estimated consumption explained none of the variation in age-0 trout mortality among lakes. We conclude that birds affect fish populations by asymmetric predation on different age (size) classes and can be important top predators that should not be ignored when characterizing freshwater food webs in lakes.
and can constrain their responses to ecological and environmental variation, such as temperature.
Here, we show for the first time that normal within-daytime fluctuations in temperature of less than
38C have large effects on personality for two species of juvenile coral reef fish in both observational
and manipulative experiments. On average, individual scores on three personality traits (PTs), activity,
boldness and aggressiveness, increased from 2.5- to sixfold as a function of temperature. However,
whereas most individuals became more active, aggressive and bold across temperature contexts (were
plastic), others did not; this changed the individual rank order across temperatures and thus altered personality.
In addition, correlations between PTs were consistent across temperature contexts, e.g. fish that
were active at a given temperature also tended to be both bold and aggressive. These results (i) highlight
the importance of very carefully controlling for temperature when studying behavioural variation among
and within individuals and (ii) suggest that individual differences in energy metabolism may contribute to
animal personality, given that temperature has large direct effects on metabolic rates in ectotherms.
that native biota use for reproductive interactions. In tropical
Australia, invasive cane toads (Rhinella marina) breed in
many of the samewaterbodies that are used by native frogs, and males of both the invader and the native taxa rely on vocal signals to attract mates. We conducted playback experiments to test the hypothesis that calls of toads may influence the calling behaviour of frogs (Limnodynastes convexiusculus and Litoria rothii). Male L. convexiusculus adjusted their calling rate and the variance in inter-call interval in response to a variety of sounds, including the calls of cane toads as well as those of other native frog species, and other anthropogenic noise, whereas L. rothii did not. Within the stimulus periods of playbacks, male L. convexiusculus called more intensely during long silent gaps than during calling blocks. Thus, males of one frog species reduced their calling rate, possibly to minimise energy expenditure during periods of acoustic interference generated by cane toads. In spite of such modifications, the number of overlapping calls (within stimulus periods) did not differ significantly from that expected by chance. In natural conditions, the calls of cane toads are continuous rather than episodic, leaving fewer gaps of silence that male frogs could exploit. Future work could usefully quantify the magnitude of temporal (e.g. diel and seasonal) and spatial overlap between calling by toads and by frogs and the impact of call-structure shifts on the ability of male frogs to attract receptive females.
Australia in 1935. Research on their ecological impact has focussed on the lethal ingestion of toxic toads by native frog-eating
predators. Less attention has been paid to the potential impacts of Cane Toads as predators, although these large anurans
sometimes eat vertebrates, such as nestling birds and bird eggs. We review published and unpublished data on interactions
between Cane Toads and Australian ground-nesting birds, and collate distributional and breeding information to identify the
avian taxa potentially at risk of having eggs or chicks eaten by Cane Toads. Cane Toads are currently sympatric with 80
ground-nesting bird species in Australia, andfive additional species of bird occur within the predicted future range of the toad.
Although many species of bird are potentially at risk, available data suggest there is minimal impact of Cane Toads on
ground-nesting species. Future research could usefully address both direct and indirect impacts of the invasion by Cane
Toads, ideally with detailedfield observations of these impacts on nesting success and of changes in bird breeding success as a
function of invasion by toads.
species distributions, abundances, and mortality rates. As with any sampling method, however, we need to
explore methodological biases in such data. First, how does an animal’s behavior (e.g., use of the center vs.
periphery of the road) influence its vulnerability to vehicular traffic? Second, how rapidly do post-mortem
processes (scavenging by other animals, destruction or displacement by subsequent vehicles) change the
numbers and locations of roadkills? Our surveys of anurans on a highway in tropical Australia show that
different anuran species are distributed in different ways across the width of the road, and that locations of live
versus dead animals sometimes differ within a species. Experimental trials show that location on the road
affects the probability of being hit by a vehicle, with anurans in the middle of the road begin hit 35% more
often than anurans on the edges; thus, center-using species aremore likely to be hit than edge-using taxa. The
magnitude of post-mortem displacement and destruction by subsequent vehicles depended on anuran species
and body size. The mean parallel displacement distance was 122.7 cm, and carcasses of thin-skinned species
exhibited greater post-mortem destruction. Scavenging raptors removed 73% of carcasses, most within a few
hours of sunrise. Removal rates were biased with respect to size and species. Overall, our studies suggest that
investigators should carefully evaluate potential biases before using roadkill counts to estimate underlying
animal abundances or mortality rates.
native prey has attracted considerable scientific
attention, whereas the reverse situation (invasive
species being eaten by native predators) has been less
frequently studied. Such interactions might affect
invasion success; an invader that is readily consumed
by native species may be less likely to flourish in its
new range than one that is ignored by those taxa.
Invasive cane toads (Rhinella marina) in Australia
have fatally poisoned many native predators (e.g.,
marsupials, crocodiles, lizards) that attempt to ingest
the toxic anurans, but birds are more resistant to toad
toxins. We quantified prey preferences of four species
of wading birds (Nankeen night heron, purple
swamphen, pied heron, little egret) in the wild, by
offering cane toads and alternative native prey items
(total of 279 trays offered, 14 different combinations
of prey types). All bird species tested preferred the
native prey, avoiding both tadpole and metamorph
cane toads. Avoidance of toads was strong enough to
reduce foraging on native prey presented in combination
with the toads, suggesting that the presence of
cane toads could affect predator foraging tactics, and
reduce the intensity of predation on native prey
species found in association with toads.
impacts of invasive species has largely focused on
negative effects, some native taxa may benefit from
invader arrival. In tropical Australia, invasive cane
toads (Bufo marinus) have fatally poisoned many
native predators (e.g., marsupials, crocodiles, lizards)
that attempt to ingest the toxic anurans, but birds
appear to be more resistant to toad toxins. We
quantified offtake of dead (road-killed) cane toads by
raptors (black kites (Milvus migrans) and whistling
kites (Haliastur sphenurus)) at a site near Darwin, in
the Australian wet-dry tropics. Raptors readily took
dead toads, especially small ones, although native
frogs were preferred to toads if available. More
carcasses were removed in the dry season than the
wet season, perhaps reflecting seasonal availability of
alternative prey. Raptors appeared to recognize and
avoid bufotoxins, and typically removed and consumed
only the toads’ tongues (thereby minimizing
toxin uptake). The invasion of cane toads thus
constitutes a novel prey type for scavenging raptors,
rather than (as is the case for many other native
predators) a threat to population viability.
have been shown to manage the risk of nest predation for subsequent re-nesting attempts by moving to a new location, placing re-nests in areas with increased cover, or changing the height above ground at which the re-nest is placed. The extent
to which this is an adaptive behaviour for birds in general is not yet clear, as existing studies are almost exclusively restricted to northern hemisphere species and species that do not breed cooperatively. Here, we examined the re-nesting behaviour of
Bell Miners (Manorina melanophrys), a species of honeyeater endemic to Australia that is both multi-brooded and also frequently re-nests soon after nesting failure; females can build up to five nests in a breeding season. We tested if these
females managed within-season nest predation risk by changing nest site characteristics (height from ground and distance between nests) between successive nesting attempts. We found that female miners did indeed manage predation risk by
reducing the height from the ground at which they placed re-nests following predation events, but contrary to our second prediction we found no difference in distances moved to re-nest after females experienced nest predation or successfully
rearing young
is rare in birds. I report an observation of an
adult Pacific Reef Egret (Egretta sacra) killing an
adult conspecific at One Tree Island, Great Barrier
Reef, Australia. The motivation and context for the
killing were not apparent. To the best of my knowledge,
this is the first report of intraspecific killing in
Pacific Reef Egrets.
or by repelling or attracting native species to the vicinity of the invader. The ongoing invasion of cane toads (Rhinella
marina) through tropical Australia might affect native frogs by affecting refuge-site availability, because both frogs
and toads frequently shelter by day in burrows. Our laboratory and field studies in the wet-dry tropics show that
native frogs of at least three species (Litoria tornieri, Litoria nasuta and Litoria dahlii) preferentially aggregate with
conspecifics, and with (some) other species of native frogs. However, the frogs rarely aggregated with cane toads
either in outdoor arenas or in standardized experimental burrows that we monitored in the field. The native frogs
that we tested either avoided burrows containing cane toads (or cane toad scent) or else ignored the stimulus (i.e.
treated such a burrow in the same way as they did an empty burrow). Native frogs selected a highly non-random
suite of burrows as diurnal retreat sites, whereas cane toads were less selective. Hence, even in the absence of toads,
frogs do not use many of the burrows that are suitable for toads. The invasion of cane toads through tropical
Australia is unlikely to have had a major impact on retreat-site availability for native frogs.
in mortality rates. Age-1 trout mortality did not differ significantly from zero in lakes without loons. Birds consumed
a small proportion of age-0 trout, and estimated consumption explained none of the variation in age-0 trout mortality among lakes. We conclude that birds affect fish populations by asymmetric predation on different age (size) classes and can be important top predators that should not be ignored when characterizing freshwater food webs in lakes.
and can constrain their responses to ecological and environmental variation, such as temperature.
Here, we show for the first time that normal within-daytime fluctuations in temperature of less than
38C have large effects on personality for two species of juvenile coral reef fish in both observational
and manipulative experiments. On average, individual scores on three personality traits (PTs), activity,
boldness and aggressiveness, increased from 2.5- to sixfold as a function of temperature. However,
whereas most individuals became more active, aggressive and bold across temperature contexts (were
plastic), others did not; this changed the individual rank order across temperatures and thus altered personality.
In addition, correlations between PTs were consistent across temperature contexts, e.g. fish that
were active at a given temperature also tended to be both bold and aggressive. These results (i) highlight
the importance of very carefully controlling for temperature when studying behavioural variation among
and within individuals and (ii) suggest that individual differences in energy metabolism may contribute to
animal personality, given that temperature has large direct effects on metabolic rates in ectotherms.
that native biota use for reproductive interactions. In tropical
Australia, invasive cane toads (Rhinella marina) breed in
many of the samewaterbodies that are used by native frogs, and males of both the invader and the native taxa rely on vocal signals to attract mates. We conducted playback experiments to test the hypothesis that calls of toads may influence the calling behaviour of frogs (Limnodynastes convexiusculus and Litoria rothii). Male L. convexiusculus adjusted their calling rate and the variance in inter-call interval in response to a variety of sounds, including the calls of cane toads as well as those of other native frog species, and other anthropogenic noise, whereas L. rothii did not. Within the stimulus periods of playbacks, male L. convexiusculus called more intensely during long silent gaps than during calling blocks. Thus, males of one frog species reduced their calling rate, possibly to minimise energy expenditure during periods of acoustic interference generated by cane toads. In spite of such modifications, the number of overlapping calls (within stimulus periods) did not differ significantly from that expected by chance. In natural conditions, the calls of cane toads are continuous rather than episodic, leaving fewer gaps of silence that male frogs could exploit. Future work could usefully quantify the magnitude of temporal (e.g. diel and seasonal) and spatial overlap between calling by toads and by frogs and the impact of call-structure shifts on the ability of male frogs to attract receptive females.
Australia in 1935. Research on their ecological impact has focussed on the lethal ingestion of toxic toads by native frog-eating
predators. Less attention has been paid to the potential impacts of Cane Toads as predators, although these large anurans
sometimes eat vertebrates, such as nestling birds and bird eggs. We review published and unpublished data on interactions
between Cane Toads and Australian ground-nesting birds, and collate distributional and breeding information to identify the
avian taxa potentially at risk of having eggs or chicks eaten by Cane Toads. Cane Toads are currently sympatric with 80
ground-nesting bird species in Australia, andfive additional species of bird occur within the predicted future range of the toad.
Although many species of bird are potentially at risk, available data suggest there is minimal impact of Cane Toads on
ground-nesting species. Future research could usefully address both direct and indirect impacts of the invasion by Cane
Toads, ideally with detailedfield observations of these impacts on nesting success and of changes in bird breeding success as a
function of invasion by toads.
species distributions, abundances, and mortality rates. As with any sampling method, however, we need to
explore methodological biases in such data. First, how does an animal’s behavior (e.g., use of the center vs.
periphery of the road) influence its vulnerability to vehicular traffic? Second, how rapidly do post-mortem
processes (scavenging by other animals, destruction or displacement by subsequent vehicles) change the
numbers and locations of roadkills? Our surveys of anurans on a highway in tropical Australia show that
different anuran species are distributed in different ways across the width of the road, and that locations of live
versus dead animals sometimes differ within a species. Experimental trials show that location on the road
affects the probability of being hit by a vehicle, with anurans in the middle of the road begin hit 35% more
often than anurans on the edges; thus, center-using species aremore likely to be hit than edge-using taxa. The
magnitude of post-mortem displacement and destruction by subsequent vehicles depended on anuran species
and body size. The mean parallel displacement distance was 122.7 cm, and carcasses of thin-skinned species
exhibited greater post-mortem destruction. Scavenging raptors removed 73% of carcasses, most within a few
hours of sunrise. Removal rates were biased with respect to size and species. Overall, our studies suggest that
investigators should carefully evaluate potential biases before using roadkill counts to estimate underlying
animal abundances or mortality rates.
native prey has attracted considerable scientific
attention, whereas the reverse situation (invasive
species being eaten by native predators) has been less
frequently studied. Such interactions might affect
invasion success; an invader that is readily consumed
by native species may be less likely to flourish in its
new range than one that is ignored by those taxa.
Invasive cane toads (Rhinella marina) in Australia
have fatally poisoned many native predators (e.g.,
marsupials, crocodiles, lizards) that attempt to ingest
the toxic anurans, but birds are more resistant to toad
toxins. We quantified prey preferences of four species
of wading birds (Nankeen night heron, purple
swamphen, pied heron, little egret) in the wild, by
offering cane toads and alternative native prey items
(total of 279 trays offered, 14 different combinations
of prey types). All bird species tested preferred the
native prey, avoiding both tadpole and metamorph
cane toads. Avoidance of toads was strong enough to
reduce foraging on native prey presented in combination
with the toads, suggesting that the presence of
cane toads could affect predator foraging tactics, and
reduce the intensity of predation on native prey
species found in association with toads.
impacts of invasive species has largely focused on
negative effects, some native taxa may benefit from
invader arrival. In tropical Australia, invasive cane
toads (Bufo marinus) have fatally poisoned many
native predators (e.g., marsupials, crocodiles, lizards)
that attempt to ingest the toxic anurans, but birds
appear to be more resistant to toad toxins. We
quantified offtake of dead (road-killed) cane toads by
raptors (black kites (Milvus migrans) and whistling
kites (Haliastur sphenurus)) at a site near Darwin, in
the Australian wet-dry tropics. Raptors readily took
dead toads, especially small ones, although native
frogs were preferred to toads if available. More
carcasses were removed in the dry season than the
wet season, perhaps reflecting seasonal availability of
alternative prey. Raptors appeared to recognize and
avoid bufotoxins, and typically removed and consumed
only the toads’ tongues (thereby minimizing
toxin uptake). The invasion of cane toads thus
constitutes a novel prey type for scavenging raptors,
rather than (as is the case for many other native
predators) a threat to population viability.