Interspecific vocal discrimination in Neotropical wrens: Responses to congeneric signals in sympatry and allopatry

When animals defend resources using territorial signals, they must distinguish between competitors and noncompetitors. Conspecific animals routinely compete for resources and regularly engage in aggressive signalling exchanges. Heterospecific animals may also compete for resources, and therefore animals may direct their aggression towards heterospecific as well as conspecific rivals. In both cases, animals should benefit by discriminating between nonthreatening individuals versus threatening conspecific and heterospecific competitors. Experience may play an important role in competitor discrimination; animals living in sympatry with heterospecific competitors may gain experience with heterospecific rivals, but animals living in allopatry will not. We investigated whether experience influences species discrimination between two congeneric Neotropical wrens (rufous-and-white wrens, Thryophilus rufalbus, and banded wrens, Thryophilus pleurostictus) that live in sympatry in some parts of their range and in allopatry in other parts of their range. We simulated the presence of male conspecific, congeneric and control intruders in the territories of rufous-and-white wrens at sites where they are sympatric or allopatric with banded wrens. If species discrimination is influenced by experience, we predicted that wrens would always respond strongly to conspecific songs, but that in sympatry, they would respond more strongly to the congeneric competitor than to the control songs. Conversely, we predicted that, in allopatry, wrens would show similarly low responses to congener and control songs. In contrast to our predictions, we found that rufous-and-white wrens discriminated between conspecific and heterospecific animals, but that this response did not differ in sympatry or allopatry, suggesting that experience with heterospecific competitors does not influence interspecific discrimination in this species. By contrasting the responses of sympatric and allopatric populations, we can better understand the effect of experience on interspecific discrimination and gain insight into the evolution of species discrimination signals. © 2015 The Association for the Study of Animal Behaviour

Tropical wrens rely more on acoustic signals than visual signals for inter- and intraspecific discrimination

Animals may use multiple signalling modalities to discriminate between conspecific versus heterospecific animals, or between individuals that represent a threat versus a mating opportunity. Multimodal signals used in intra- and interspecific discrimination can serve as redundant signals, or each modality may convey unique information. Furthermore, signals in different modalities may show different transmission properties through different habitats. In this study we investigated how two congeneric wrens, rufous-and-white wrens, Thryophilus rufalbus, and banded wrens, Thryophilus pleurostictus, use acoustic and visual signals for species discrimination in tropical forest habitats. We coupled song playback experiments with visual models to assess the importance of these signals, both in combination and in isolation. We assessed vegetation density in the territories of both species to assess whether more densely vegetated territories influence the use of visual signals. We presented both rufous-and-white wrens and banded wrens with conspecific and congeneric song treatments, model treatments and song-accompanied-by-model treatments. We found that both species responded strongly to song and song-accompanied-by-model treatments, but showed little or no response when the model was presented alone. These results suggest that wrens rely heavily on acoustic signals and very little on visual signals for discrimination. The species differed in their response to conspecific and congeneric trials, with rufous-and-white wrens showing little response to the congeneric trials but banded wrens responding strongly to both conspecific and congeneric trials. The asymmetrical response to the playback trials suggests that there may be a social dominance relationship between these two species, with rufous-and-white wrens being dominant over banded wrens. No previous studies have investigated the relative importance of acoustic and visual signals in males and females for species discrimination. Our results suggest that acoustic signals are more important than visual signals for inconspicuous animals living in dense environments. © 2016 The Association for the Study of Animal Behaviou

Comprehensive estimation of spatial and temporal migratory connectivity across the annual cycle to direct conservation efforts

Migratory connectivity is the degree to which populations are linked in space and time across the annual cycle. Low connectivity indicates mixing of populations while high connectivity indicates population separation in space or time. High migratory connectivity makes individual populations susceptible to local environmental conditions; therefore, evaluating migratory connectivity continuously across a species range is important for understanding differential population trends and revealing places and times contributing to these differences. The common nighthawk Chordeiles minor is a widespread, declining, long‐distance migratory bird. Variable population trends across the nighthawk breeding range suggest that knowledge of migratory connectivity is needed to direct conservation. We used GPS tags to track 52 individuals from 12 breeding populations. We estimated migratory connectivity as 0.29 (Mantel coefficient: 0 = no connectivity, 1 = full connectivity) between the breeding and wintering grounds. We then estimated migratory connectivity at every latitude (spatial connectivity) or day (temporal connectivity) of migration and smoothed those migratory connectivity estimates to produce continuous migratory connectivity ‘profiles'. Spatial and temporal connectivity were highest during migration through North America (around 0.3–0.6), with values generally around 0 in Central and South America due to mixing of populations along a common migratory route and similar migration timing across populations. We found local peaks in spatial and temporal connectivity during migration associated with crossing the Gulf of Mexico. We used simulations to estimate the probability that our method missed peaks (spatial: 0.12, temporal: 0.18) or detected false peaks (spatial: 0.11, temporal: 0.37) due to data gaps and showed that our approach remains useful even for sparse and/or sporadic location data. Our study presents a generalizable approach to evaluating migratory connectivity across the full annual cycle that can be used to focus migratory bird conservation towards places and times of the annual cycle where populations are more likely to be limited