Search

Elaborate visual signals play a crucial role in communication between many breeding animals, often evolving through female mate choice and male-male competition. Neotropical Yellow Toads (Incilius luetkenii) exhibit a temporary elaborate visual trait during their brief annual mating events, transitioning from a drab, female-like brown coloration to a vibrant lemon-yellow. They engage in scramble competition, where males physically compete with both lone and amplectant males for access to females. Previous studies suggest that male color may serve as a sex identification signal in the toads' large breeding aggregations, and that females do not appear to choose males based on color. In this study we investigated whether variation in male coloration functions as an intrasexual signal during male-male interactions. Using realistic robotic model toads in a two-choice arena, we addressed two questions. First, do male Yellow Toads respond differently to a lone male versus a male in amplexus with a female when both males are the same color? Secondly, do male Yellow Toads respond differently to two amplectant males varying in the brightness of their yellow coloration? Males approached the amplectant pair nearly twice as often as the lone male, although this pattern was not statistically significant. Males did not exhibit a differential reaction to bright amplectant males versus dull amplectant males. Therefore, variation in male yellow color and the presence of a female do not appear to influence male-male competitive behavior. Overall, this study contributes to our understanding of temporary color change in vibrantly colored anuran species. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity allows organisms to adjust the timing of life‐history events in response to environmental and demographic conditions. Shifts by individuals in the timing of breeding with respect to variation in age and temperature are well documented in nature, and these changes are known to scale to affect population dynamics. However, relatively little is known about how organisms alter phenology in response to other demographic and environmental factors. We investigated how pre‐breeding temperature, breeding population density, age, and rainfall in the first month of life influenced the timing and plasticity of lay date in a population of Savannah Sparrows (Passerculus sandwichensis) monitored over 33 yr (1987–2019). Females that experienced warmer pre‐breeding temperatures tended to lay eggs earlier, as did older females, but breeding population density had no effect on lay date. Natal precipitation interacted with age to influence lay date plasticity, with females that experienced high precipitation levels as nestlings advancing lay dates more strongly over the course of their lives. We also found evidence for varied pace of life; females that experienced high natal precipitation had shorter lifespans and reduced fecundity, but more nesting attempts over their lifetimes. Rainfall during the nestling period increased through time, while population density and fecundity declined, suggesting that increased precipitation on the breeding grounds may be detrimental to breeding females and ultimately the viability of the population as a whole. Our results suggest that females adjust their laying date in response to pre‐breeding temperature, and as they age, while presenting new evidence that environmental conditions during the natal period can affect phenological plasticity and generate downstream, population‐level effects. [ABSTRACT FROM AUTHOR]

For territorial animals, the behavior of conspecific neighbors sets the social context of communication. Despite numerous investigations of vocalizations related to territory defense and mate attraction, the effect of neighbor density on animal vocal behavior has received little attention, particularly in tropical animals and animals where both sexes produce complex acoustic signals. In this study, we used an innovative multispeaker playback experiment to manipulate the apparent density of neighbors in rufous-and-white wrens, Thryophilus rufalbus , living in Costa Rica's tropical dry forest. In this tropical songbird, both males and females defend year-round territories and sing complex, learned songs for territory defense. We recorded the singing behavior of 24 subjects (12 pairs), and then we used an array of 6 loudspeakers to simulate the presence of 6 new territorial neighbors (3 simulated pairs) outside each subject pair's breeding territory. The stimuli persisted for 3 consecutive days, with both male and female songs broadcast at a natural rate from dawn to dusk. We found that the mean male song rate increased by almost 50% in response to the simulated increase in local density. Females showed less frequent song-type switching rates following the simulated increase in local density, although it was a marginal increase. These findings reveal that male and female songbirds' vocal behavior varies with the local density of territorial neighbors. We conclude that birds are sensitive to acoustic signals of conspecific density arising from sounds beyond their territory boundaries, and that they use this public information to guide their vocal behavior., Competing Interests: None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology.)