Do European starlings prefer light environments containing UV?

Many captive birds are kept in artificial lighting that is typically deficient in ultraviolet (UV) wavelengths. Most birds can perceive the range of light that humans see but also have an additional retinal cone type that is tuned to UV wavelengths. Consequently, artificial lighting may be detrimental as it might limit the functionality of their vision. We examined the preferences of European starlings, Sturnus vulgaris, for various artificial light environments. In our first experiment, groups of starlings showed a preference for environments that contained UV (UV+) over those where UV wavelengths had been removed (UV -). This preference was not affected by the sex of the individuals within the group or, as shown in a later experiment, by whether the birds had been previously housed in UV+ or UV - conditions. In contrast, individual starlings showed no preference for UV+ over UV - environments, although the power of our test was low. In a subsequent experiment, starling groups preferred the higher of two light intensities that were presented; however, equalizing the overall quantal flux between UV+ and UV - extinguished any preference for UV+ over UV -. The group preference for UV+ conditions in the first experiment may therefore have resulted from a preference for brighter conditions rather than a specific preference for UV. However, equalizing the quantal flux may not equalize perceived brightness, because it is not known how birds' visual systems weight input from each cone type. We conclude that, for nonbreeding, group-housed captive starlings, there is no positive evidence of a preference for the presence of UV as a specific wavelength. (C) 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Preferences for ultraviolet partners in the blue tit

The preference of female blue tits, Parus caeruleus, is correlated with the brightness of the ultraviolet (UV) crest; there is also assortative mating with respect to the crest's UV/violet chroma. However, manipulation of plumage reflectance is necessary to infer a direct causal link between UV plumage and mate choice. We gave both male and female blue tits a choice between a W-reflecting ('UV+') partner and a partner whose UV plumage reflectance had been removed ('UV-'). Male blue tits significantly preferred UV+ females. Similarly, female blue tits tended to prefer UV-reflecting males, but their UV+ preferences were nonsignificant. Neither sex showed a preference when conspecifics were replaced by a heterospecific. This study suggests mutual mate choice but male choice may be more strongly influenced by the visual appearance of potential mates. This is one of a few studies to show male mate preferences and the first demonstration of a direct relationship between UV reflectance and;male mate choice. (C) 1999 The Association for the Study of Animal Behaviour.

Ultraviolet vision and band-colour preferences in female zebra finches, Taeniopygia guttata

Zebra finches have previously been found to have preferences for particular colours of both natural and artificial traits among opposite sex conspecifics. For example, in some studies female zebra finches preferred males wearing red leg bands to orange-banded and unbanded birds and rejected light green-banded males. In other studies, females also preferred males with red beaks to orange-beaked males. However, several authors have failed to replicate these results. We show that females may fail to show a colour preference because of the absence or removal of ultraviolet light under experimental conditions. In mate-choice trials, females observing males through filters that transmitted ultraviolet preferred red-banded males but where females viewed males through ultraviolet-blocking filters, no such preference was observed. Further investigation revealed that the lack of a colour preference when ultraviolet was absent was probably due to the change in overall appearance of the bird, rather than the change in appearance of the rings themselves. This work highlights the importance of proper consideration of the sensory capabilities of animals in experimental design, particularly with regard to the role of ultraviolet light in avian colour perception. (C) 1997 The Association for the Study of Animal Behaviour.

Context-dependent visual preferences in starlings and blue tits: mate choice and light environment

There is considerable interest in the role that ultraviolet (UV) cues play in the foraging and mate choice decisions of birds. However, with the exception of the zebra finch, Taeniopygia guttata, it is not yet clear whether ultraviolet preferences are context specific, or whether birds show a general preference for full-avian-spectrum environments 320-700 nm) irrespective of the activity in which they are engaged. We investigated whether European starlings, Sturnus vulgaris, and blue tits, Parus caeruleus, show general (nonresource based) or context-specific preferences for full-spectrum environments. We found that neither species showed a general preference for UV-present (UV+) over UV-deficient (UV-) environments, when those environments contained no resources (experiment 1). Furthermore, neither species showed a UV+ preference when cages contained food, water and perches (starlings; experiment 2) or food, perches and heterospecifics (blue tits; Hunt et al. 1999. Animal Behaviour, 58, 809-815). However, both species did show highly significant preferences for UV+ conditions when viewing potential mates. Such experiments are necessary before one can conclude that particular wavebands have specific relevance to mate choice. In fact, our results suggest that the importance of particular wavelength compositions do indeed vary with behavioural context. (C) 2002 The Association for the Study of Animal Behaviour.

Does the ring species concept predict vocal variation in the crimson rosella, Platycercus elegans, complex?

Vocal variation may be important in population divergence. We studied geographical variation in contact calls of parrots of the crimson rosella, Platycercus elegans, complex, which is characterized by striking geographical plumage coloration variation. This complex has long been considered a rare example of a ring species (where two divergent forms coexist in sympatry but are connected by a chain of intermediate populations forming a geographical ring). We tested whether contact call variation is consistent with the ring species hypothesis. We recorded calls throughout the ring, including several sites from the three main population groups forming the ring and interfaces between them. We analysed duration, peak frequency, fundamental frequency and frequency modulation. We found significant differences, particularly in fundamental frequency and frequency modulation, at multiple biogeographical scales ranging from local populations to subspecies level. Discriminant function analyses showed some populations could be reliably discriminated from call structure. However, our results provided little support for three key predictions of the ring species hypothesis: (1) calls of the terminal, most divergent forms were not significantly different in three of the four acoustic variables, and differences did not appear to be maintained in sympatry, (2) phenotypically/geographically intermediate populations were not characterized by intermediate calls, and (3) call variation was not concordant with geographical sequence around the ring from one terminal form to the other. Our results underscore the emerging view that the evolutionary histories and phenotypic variability of many long-held ring species may be inadequately described by the ring species hypothesis and require alternative explanations. (C) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Do male guppies distinguish virgin females from recently mated ones?

In some mating systems males should benefit from mating with virgin females because of their higher reproductive value. We determined experimentally whether and how males distinguish between virgin and recently mated females in the guppy, Poecilia reticulata, a promiscuous livebearer. In a free-swimming experiment, males showed flexible mating behaviour by adjusting their tactics according to the mating status of the female they encountered, virgin or mated. Males followed, nipped and copulated with virgins more than with mated females, but they performed more sneaky copulations with mated females, possibly because the latter were more reluctant to mate than virgin females. When, in another set of experiments, males received only the visual cues of both virgins and mated females they showed no preference for either, but when they were exposed only to the female olfactory cues, they associated considerably more with the smell of virgin females. These results suggest that male guppies assess female behavioural and olfactory cues to determine female virginity and then use different mating tactics depending on the female's status. It is possible that the changes in male mating behaviour increase male reproductive success.

Vocal mimicry in songbirds

Baylis (1982, Acoustic Communication in Birds, Academic Press) decried the serious lack of experimental verification for the various hypotheses proposed to explain vocal mimicry in songbirds. With few exceptions, our understanding of the function and acquisition of this fascinating behaviour seems to have scarcely progressed. We examine the proposed functional explanations and supporting evidence, and summarize advances made since Baylis's (1982) review. We conclude that there is no compelling evidence to support any of the functional hypotheses but, rather, that almost all of the data concerning song mimicry are consistent with the learning mistakes hypothesis, whereby birds learn simple and common sounds, frequently using them in inappropriate contexts. Additionally, many apparently mimicked sounds are calls, not songs, which themselves may not be learned by the models. It is plausible that many examples of call mimicry are, in fact, due to evolutionary convergence.

Male mate-searching strategies and female cues: how do male guppies find receptive females?

Locating potential mates is critical to mating. We studied males’ association with females and mate-searching patterns in the guppy, Poecilia reticulata, a promiscuous live-bearer. In the field, we examined whether male guppies respond differently to a shoal of conspecific fish based on the members of the shoal. We found that more males were attracted to shoals that contained receptive females than to shoals of nonreceptive females or males. We also conducted laboratory experiments to investigate how males use olfactory cues of nonreceptive and receptive females to search for and associate with females. We gave males the option to associate with nonreceptive females when olfactory cues of receptive or nonreceptive females were present and absent, and when olfactory cues were presented alone. Males associated with females most strongly when both cues were presented simultaneously, but when cues were presented separately males’ association with females differed with respect to the olfactory cues that were added. Males associated with females equally with visual and olfactory cues presented separately when the odour cues were from receptive females. However, when the odour cues were from nonreceptive females, males associated with females less with olfactory than visual cues. Searching activity increased when males had access only to olfactory cues. Taken together these results suggest that olfactory cues influence males’ association with females and searching behaviour, and these changes in behaviour are likely to maximize a male’s opportunity to encounter receptive females.

Editorial : Q & A John A. Endler

John A. Endler is a Professor of Sensory Ecology and Evolution at Deakin University and an Adjunct professor of Zoology at James Cook University, both in Australia. He regards himself as a 19th century natural historian who uses 21st century techniques to answer questions generated originally from field observations. His research is in the area of overlap among Evolutionary Biology, Sensory Ecology, Behavioural Ecology, Animal Behaviour, Neuroethology and Biophysics. He enjoys combining field work, field experiments, lab work, and theoretical methods as well as constructing electromechanical-optical equipment and software for himself and students.