Micro-Habitat Influence on the Advertisement Call Structure and Sound Propagation Efficiency of Hypsiboas crepitans (Anura: Hylidae)

Localizing wild chimpanzees with passive acoustics

Localizing wildlife contributes in multiple ways to species conservation. Data on animal locations can reveal elements of social behavior, habitat use, population dynamics, and be useful in calculating population density. Acoustic localization systems (ALS) are a non‐invasive method widely used in the marine sciences but not well established and rarely employed for terrestrial species.

We deployed an acoustic array in a mountainous environment with heterogeneous vegetation, comprised of four custom‐built GPS synchronized acoustic sensors at about 500 m intervals in Issa Valley, western Tanzania, covering an area of nearly 2 km². Our goal was to assess the precision and error of the estimated locations by conducting playback tests, but also by comparing the estimated locations of wild chimpanzee calls with their true locations obtained in parallel during follows of individual chimpanzees. We assessed the factors influencing localization error, such as wind speed and temperature, which fluctuate during the day and are known to affect sound transmission.

We localized 282 playback sounds and found that the mean localization error was 27 ± 21.8 m. Localization was less prone to error and more precise during early mornings (6:30 h) compared to other periods. We further localized 22 wild chimpanzee loud calls within 52 m of the location of a researcher closely following the calling individuals.

We demonstrate that acoustic localization is a powerful tool for chimpanzee monitoring, with multiple behavioral and conservation applications. Its applicability in studying social dynamics and revealing density estimation among many others, especially but not exclusively for loud calling species, provides an efficient way of monitoring populations and informing conservation plans to mediate species loss.

How plants affect amphibian populations

Descriptions of amphibian habitat, both aquatic and terrestrial, often include plants as characteristics but seldom is it understood whether and how those plants affect amphibian ecology. Understanding how plants affect amphibian populations is needed to develop strategies to combat declines of some amphibian populations. Using a systematic approach, we reviewed and synthesized available literature on the effects of plants on pond-breeding amphibians during the aquatic and terrestrial stages of their life cycle. Our review highlights that plant communities can strongly influence the distribution, abundance, and performance of amphibians in multiple direct and indirect ways. We found three broad themes of plants' influence on amphibians: plants can affect amphibians through effects on abiotic conditions including the thermal, hydric, and chemical aspects of an amphibian's environment; plants can have large effects on aquatic life stages through effects on resource quality and abundance; and plants can modify the nature and strength of interspecific interactions between amphibians and other species - notably predators. We synthesized insights gained from the literature to discuss how plant community management fits within efforts to manage amphibian populations and to guide future research efforts. While some topical areas are well researched, we found a general lack of mechanistic and trait-based work which is needed to advance our understanding of the drivers through which plants influence amphibian ecology. Our literature review reveals the substantial role that plants can have on amphibian ecology and the need for integrating plant and amphibian ecology to improve research and management outcomes for amphibians.

Transmission of high-frequency vocalizations from hummingbirds living in diverse habitats

Some species of Andean hummingbirds produce high-frequency vocalizations which exceed the vocal range of most birds. They also challenge our understanding of the role of habitat structure in the evolution of vocal signals because these hummingbirds live in strikingly different habitats, ranging from cloud forest to high-altitude grasslands. Although these vocalizations are produced at high frequencies, they exhibit considerable variation in frequency content and temporal structure. The calls of the hummingbirds from the cloud forest are simpler and have a narrow frequency range compared to the complex song of the grasslands hummingbird. We hypothesized that each of the three high-frequency vocalizations is adapted for transmission in their habitat. We characterized the transmission of high-frequency vocal signals in the cloud forest and in the grasslands. All vocalizations attenuated and degraded substantially at short distances, suggesting that they are adapted for short-range communication. The simple vocalizations of the cloud-forest species transmitted better in both environments compared to the complex song of the grasslands hummingbird, probably due to relaxed constraints for high-frequency sounds in open habitats.

Environmental and morphological constraints interact to drive the evolution of communication signals in frogs

Animals show a rich diversity of signals and displays. Among the many selective forces driving the evolution of communication signals, one widely recognized factor is the structure of the environment where animals communicate. In particular, animals communicating by sounds often emit acoustic signals from specific locations, such as high up in the air, from the ground or in the water. The properties of these different display sites may impose different constraints on sound production, and therefore drive signal evolution. Here, we used comparative phylogenetic analyses to assess the relationship between calling site (aquatic versus nonaquatic), body size and call dominant frequency of 160 frog species from the families Ranidae, Leptodactylidae and Hylidae. We found that the frequency of frogs calling from the water was lower than that of species calling outside of the water, a trend that was consistent across the three families studied. Furthermore, phylogenetic path analysis revealed that call site had both direct and indirect effects on call frequency. Indirect effects were mediated by call site influencing male body size, which in turn was negatively associated with call frequency. Our results suggest that properties of display sites can drive signal evolution, most likely not only through morphological constraints imposed on the sound production mechanism, but also through changes in body size, highlighting the relevance of the interplay between morphological adaptation and signal evolution. Changes in display site may therefore have important evolutionary consequences, as it may influence sexual selection processes and ultimately may even promote speciation.

Combined effects of physiological condition and environmental attributes in determining call plasticity

Evidence is growing on the ability of anurans to make immediate call adjustments in response to the propagation properties of the environment. However, our understanding of such flexibility is typically based on dichotomous stimuli (i.e. presence/absence), while its condition-dependence has been little explored. We experimentally studied the ability of adjustment and its condition dependence of advertisement calls of Hypsiboas pulchellus in response to different levels of attenuation. Individuals modified most call parameters analyzed, although the direction of adjustments was contingent on individual identity, level of attenuation and trait category (i.e. spectral or temporal). Under low attenuation conditions males lengthened some call elements, partially supporting the hypothesis of plasticity oriented towards maintaining signal transmission, but this trend was not present in the high attenuation treatment. Also, under both attenuation treatments males gave higher frequency notes, as expected from an energy-saving response to changes in social environment or reducing attractiveness due to risk perception. Across treatments individuals in better condition tended to exhibit higher plasticity. These results indicate that call structure could depend on the integration of different cues such as habitat propagation characteristics, acoustic competition for females, and predation risk, while the ability to behave flexibly depends on current body reserves.