Negotiation over offspring care--how should parents respond to each other's efforts?

Models of biparental care predict that parents should compensateincompletely for any change in their partner's investment. Experimentaltests have, however, yielded results that range from full compensation,through a lack of any reaction, to a matching response. Herewe suggest a new, adaptive explanation for such variation. Buildingon an approach developed by McNamara et al., we incorporateuncertainty regarding brood need or value into a game-theoreticalmodel of biparental negotiation over offspring care. We showthat when each parent has only partial information, greatereffort invested by one serves as a signal to the other of broodneed. This favors a matching response by the focal parent'smate, whereas the impact of increased effort on the marginalvalue of investment favors a compensatory response. The netoutcome depends on the relative strength of these two effects.The greater the variation in brood need compared with parentalstate, the weaker the predicted level of compensation, and themore likely matching is to occur. Our model also suggests whymales and females might respond differently to each other. Ifthere is an informational asymmetry between them, then the parentthat is better informed about brood need should work harder,respond more strongly to changes in brood need, be less sensitiveto changes in the cost of feeding, and compensate more stronglyfor changes in partner effort. If the asymmetry is very great,the poorly informed parent may even match changes in its partner'swork rate.     

Interspecific responses to distress calls in bats (Chiroptera: Vespertilionidae): a function for convergence in call design?

Distress calls were recorded from three sympatric species of pipistrelle bat (Pipistrellus nathusii, P. pipistrellus and P. pygmaeus) in England and Northern Ireland. At foraging sites, we conducted playback experiments, consisting of experimental distress call sequences from each species and control sequences of random noise and sound recorded with no bats present. We measured response by simultaneously recording ultrasound during playbacks and counting the echolocation pulses above a predetermined threshold which were then identified to species. All three species responded to each other's calls. The number of recorded echolocation pulses of all species increased eight-fold, on average, during the playback of distress call sequences compared with the playback of ultrasonic noise, and four-fold compared with the playback of silence. In a separate playback experiment, the number of echolocation pulses of P. pygmaeus increased 14-fold during the playback of distress calls of four endemic species of bat from Madagascar (Emballonura atrata, Myotis goudoti, Miniopterus majori and M. manavi) compared with the playback of silence. This increased response might have been caused by the high calling rates of the Malagasy species. Distress calls of P. nathusii, P. pipistrellus and P. pygmaeus were structurally convergent, consisting of a series of downward-sweeping, frequency-modulated elements of short duration and high intensity with a relatively strong harmonic content. Selection may favour convergence in the structure of distress calls among bat species, if attracting heterospecifics increases the chance of repelling predators by mobbing.     

Do mobbing calls affect the perception of predation risk by forest birds?

We report the results of two field experiments assessing whether exposure to mobbing calls, which usually indicates the presence of a predator, elicits changes in risk perception as measured by the willingness of forest birds to enter or cross gaps in forest cover. In the first experiment, we tested the prediction that wintering black-capped chickadees,Poecile atricapilla , will travel less in open areas to seek food from a feeder during a simulated mobbing event than they will under control conditions. The number of visits to feeders decreased at increasing distances from forest edges (0-10 m) when mobbing calls were played. Mobbing calls increased the overall rate of visits to feeders, but lowered the rate of visits to feeders located at 10 m from forest edges. By contrast, when a stuffed merlin, Falco columbarius, was placed near the feeder, chickadees rarely visited the feeder, regardless of the distance to forest edge. In the second experiment, we tested the prediction that breeding male red-eyed vireos, Vireo olivaceus, would be less attracted to the song of a nearby red-eyed vireo after a playback of a mobbing event than after a ‘neutral’ sound stimulus, especially if they had to cross an open area. Vireos were as willing to enter or cross gaps in forest cover following exposure to mobbing calls, although they responded more frequently to conspecific song under forest cover than across gaps. Our results suggest that forest birds under cover assess the risk of a mobbing situation largely on the basis of the distance to the cause of mobbing. It follows that a trade-off between risk and reward may not occur with mobbing birds, unless mobbing occurs far outside forest cover and/or at very close range (<5 m) to a predator. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

A morphospace‐based test for competitive exclusion among flying vertebrates: did birds,bats and pterosaurs get in each other's space?

Three vertebrate groups – birds, bats and pterosaurs – have evolved flapping flight over the past 200 million years. This innovation allowed each clade access to new ecological opportunities, but did the diversification of one of these groups inhibit the evolutionary radiation of any of the others? A related question is whether having the wing attached to the hindlimbs in bats and pterosaurs constrained their morphological diversity relative to birds. Fore‐ and hindlimb measurements from 894 specimens were used to construct a morphospace to assess morphological overlap and range, a possible indicator of competition, among the three clades. Neither birds nor bats entered pterosaur morphospace across the Cretaceous–Paleogene (Tertiary) extinction. Bats plot in a separate area from birds, and have a significantly smaller morphological range than either birds or pterosaurs. On the basis of these results, competitive exclusion among the three groups is not supported.     

Does sociality drive the evolution of communicative complexity? A comparative test with ground-dwelling sciurid alarm calls

While sociality has been hypothesized to drive the evolution of communicative complexity, the relationship remains to be formally tested. We derive a continuous measure of social complexity from demographic data and use this variable to explain variation in alarm repertoire size in ground-dwelling sciurid rodents (marmots, Marmota spp.; prairie dogs, Cynomys spp.; and ground squirrels, Spermophilus spp.). About 40% of the variation in alarm call repertoire size was explained by social complexity in the raw data set. To determine the degree to which this relationship may have been influenced by historical relationships between species, we used five different phylogenetic hypotheses to calculate phylogenetically independent contrasts. Less variation was significantly explained in contrast-based analyses, but a general positive relationship remained. Social complexity explained more variation in alarm call repertoire size in marmots, while sociality explained no variation in repertoire size in prairie dogs and no variation in phylogenetically based analyses of squirrels. In most cases, substantial variation remained unexplained by social complexity. We acknowledge that factors other than social complexity, per se, may contribute to the evolution of alarm call repertoire size in sciurid rodents, and we discuss alternative hypotheses. Our measure of social complexity could be used by other researchers to test explicit evolutionary hypotheses that involve social complexity.     

A non-vocal alarm? Effects of wing trill playbacks on antipredator responses in the scaled dove

acta ethologica - Animals have evolved a variety of mechanisms to detect and avoid predation. The non-vocal sounds produced by some bird species during takeoff flights have been considered to...     

Are species' responses to global change predicted by past niche evolution?

Predicting how and when adaptive evolution might rescue species from global change, and integrating this process into tools of biodiversity forecasting, has now become an urgent task. Here, we explored whether recent population trends of species can be explained by their past rate of niche evolution, which can be inferred from increasingly available phylogenetic and niche data. We examined the assemblage of 409 European bird species for which estimates of demographic trends between 1970 and 2000 are available, along with a species-level phylogeny and data on climatic, habitat and trophic niches. We found that species'' proneness to demographic decline is associated with slow evolution of the habitat niche in the past, in addition to certain current-day life-history and ecological traits. A similar result was found at a higher taxonomic level, where families prone to decline have had a history of slower evolution of climatic and habitat niches. Our results support the view that niche conservatism can prevent some species from coping with environmental change. Thus, linking patterns of past niche evolution and contemporary species dynamics for large species samples may provide insights into how niche evolution may rescue certain lineages in the face of global change.     

Disarmed by domestication? Induced responses to browsing in wild and cultivated olive

Populations of plants and animals are almost always made up of individuals of different sizes. In populations where cannibalism is common, this size variation can influence rates of mortality and growth and affect population regulation. Size variation can be caused by a variety of mechanisms. One of these is due to size-specific responses to the threat of predation by potentially cannibalistic conspecifics. We investigated the role of anti-predator behavior in size structure development within single-aged cohorts of Arizona tiger salamander larvae. In a laboratory experiment, we show that size variation increases over time within groups of salamanders, even if they are fed in isolation. We also show that increasing the size of neighbors decreases the feeding rate of small salamander larvae. However, increasing density of neighbors did not have a significant effect on feeding rate. These results are consistent with the hypothesis that size variation among tiger salamander larvae is, in part, a result of size-specific responses to predation risk. We discuss the potential for feedback between size structure development, predation risk, and rates of cannibalism. Received: 5 October 1999 / Accepted: 8 February 2000     

Are stress responses to geomagnetic storms mediated by the cryptochrome compass system?

A controversial body of literature demonstrates associations of geomagnetic storms (GMS) with numerous cardiovascular, psychiatric and behavioural outcomes. Various melatonin hypotheses of GMS have suggested that temporal variation in the geomagnetic field (GMF) may be acting as an additional zeitgeber (a temporal synchronizer) for circadian rhythms, with GMS somehow interfering with the hypothesized system. The cryptochrome genes are known primarily as key components of the circadian pacemaker, ultimately involved in controlling the expression of the hormone melatonin. Cryptochrome is identified as a clear candidate for mediating the effect of GMS on humans, demonstrating the prior existence of several crucial pieces of evidence. A distinct scientific literature demonstrates the widespread use of geomagnetic information for navigation across a range of taxa. One mechanism of magnetoreception is thought to involve a light-dependent retinal molecular system mediated by cryptochrome, acting in a distinct functionality to its established role as a circadian oscillator. There is evidence suggesting that such a magnetosense--or at least the vestiges of it--may exist in humans. This paper argues that cryptochrome is not acting as secondary geomagnetic zeitgeber to influence melatonin synthesis. Instead, it is hypothesized that the cryptochrome compass system is mediating stress responses more broadly across the hypothalamic-pituitary-adrenal (HPA) axis (including alterations to circadian behaviour) in response to changes in the GMF. Two conceptual models are outlined for the existence of such responses--the first as a generalized migrational/dispersal strategy, the second as a stress response to unexpected signals to the magnetosense. It is therefore proposed that GMS lead to disorientation of hormonal systems in animals and humans, thus explaining the effects of GMS on human health and behaviour.     

Interspecific visitation of cattle and badgers to fomites: A transmission risk for bovine tuberculosis?

In Great Britain and Ireland, badgers (Meles meles) are a wildlife reservoir of Mycobacterium bovis and implicated in bovine tuberculosis transmission to domestic cattle. The route of disease transmission is unknown with direct, so‐called “nose‐to‐nose,” contact between hosts being extremely rare. Camera traps were deployed for 64,464 hr on 34 farms to quantify cattle and badger visitation rates in space and time at six farm locations. Badger presence never coincided with cattle presence at the same time, with badger and cattle detection at the same location but at different times being negatively correlated. Badgers were never recorded within farmyards during the present study. Badgers utilized cattle water troughs in fields, but detections were infrequent (equivalent to one badger observed drinking every 87 days). Cattle presence at badger‐associated locations, for example, setts and latrines, were three times more frequent than badger presence at cattle‐associated locations, for example, water troughs. Preventing cattle access to badger setts and latrines and restricting badger access to cattle water troughs may potentially reduce interspecific bTB transmission through reduced indirect contact.     

Who cares who calls? Selective responses to the lost calls of socially dominant group members in the white‐faced capuchin (Cebus Capucinus)

In many social mammals and birds, soft vocalizations are habitually produced during dispersed moving and foraging, the function being to maintain contact and regulate spacing between group members. In some species, much louder calls are given sporadically by specific individuals when they become separated from the group, or 'lost'. The function of these calls has seldom been specifically tested, particularly among social primates, but is often assumed to involve regaining contact with the group based on a combination of individually distinctive calls and antiphonal responses to them from within the group. To test these assumptions, we conducted research on two groups of white-faced capuchins (Cebus capucinus) in Costa Rica. We analyzed 82 bouts of 'lost' calls given by 13 different adult individuals when separated from the group and the antiphonal responses they elicited. Lost calls were individually distinctive and were answered in 35% of calling episodes. Answers were selective: dominant males and females were answered more than were subordinate callers of either sex. As a result, dominant callers relocated and returned to the group more quickly than did subordinate callers. We discuss the potential proximate motivations for, and ultimate benefits of, such selective answering of dominant group members.     

Differences in acute stress responses between wild-caught and captive-bred birds: a physiological mechanism contributing to current avian invasions?

Current avian invasions are often the result of exotic birds accidentally escaping from cages. It has been hypothesised that the higher invasiveness of wild-caught cage-birds compared to captive-bred ones could be related to the loss of ability in captive-bred birds to cope with new environments. The acute stress response plays an important role in how animals cope with challenges because elevated corticosterone (CORT) levels can mediate learning and memory consolidation and help to increase their survival prospects. We experimentally tested whether exotic wild-caught and captive-bred cage-birds differ in their responses to acute stress using a representative sample of parrots. Wild-caught individuals showed longer CORT responses to acute stress than captive-bred ones, both at inter- and intra-specific levels when comparing wild-birds to the first generation born in captivity. Captive-bred birds may have attenuated their CORT responses due to acclimation, while high mortality rates during the international trade of wild-caught birds could have selected those individuals that are better able to cope with stress. We suggest that the longer acute response found in wild-caught parrots could help them to escape from cages and survive when facing challenges in new wild environments, possibly contributing to their higher invasiveness.     

Do Arctic-nesting birds respond to earlier snowmelt? A multi-species study in north Yukon, Canada

Climate change has altered the timing of many ecological processes, especially in the Arctic. The initiation of nesting is a key signal of phenological changes in Arctic-nesting birds, and is possibly connected to the circumpolar trend of earlier snowmelt. We collected data on lay dates of 7 bird species, representing shorebirds, passerines, a bird of prey, and seabirds, nesting on Herschel Island, Yukon, Canada, in the years 1984–1986 and 2007–2009. Snowmelt was significantly earlier in the 2007–2009 period. Shorebirds and passerines showed trends to earlier lay dates in conjunction with earlier snowmelt; the other species did not. The strength of response in lay date was correlated with the general categories of foods known to be used by study species. However, six species showed a longer time interval between snowmelt and egg-laying in early compared to late springs, suggesting the need for further monitoring of how robust their responses to snowmelt are in the future.