Brood size and its importance for nestling growth in the Biscutate Swift (Streptoprocne biscutata, Aves: Apodidae)

Many Apodidae, including Streptoprocne biscutata (Sclater, 1866), drop eggs from their nests during incubation. This is interpreted as nest site competition or accident. We provide evidence that egg ejection is deliberate and that this behaviour controls the brood size. Brood sizes were manipulated and nestling growth was measured to test the hypothesis that pairs can regulate brood size during incubation based on current ability to rear nestlings. Natural (control) broods with one, two and three nestlings, and manipulated (experimental) broods reduced to one and increased to two and three young were monitored. Growth rates were measured based on weight, and wing, tail and tarsus lengths of natural and manipulated broods. We compared the slopes of each measure's regression lines of the nestlings of each brood size by t-test. Nestling growth of control nests was similar and relatively little associated with brood size. In broods reduced to one nestling, weight, wing and tail had greater growth rates, and in broods increased to three nestlings growth rates were lower. Weight was most, and tarsus length least influenced by brood size. In general, nestling growth of manipulated nests was inversely proportional to brood size. The results suggest that pairs with larger clutches are in better physical conditions than others. Thus, in experimental broods, pairs are over or under-loaded because feeding activities increase or decrease and these changes affect the growth rate of the nestlings. The present study suggests that egg ejection can control brood size. This behaviour is probably stimulated by physical changes in the adult birds during incubation

Brood size and its importance for nestling growth in the Biscutate Swift (Streptoprocne biscutata, Aves: Apodidae)

Abstract Many Apodidae, including Streptoprocne biscutata (Sclater, 1866), drop eggs from their nests during incubation. This is interpreted as nest site competition or accident. We provide evidence that egg ejection is deliberate and that this behaviour controls the brood size. Brood sizes were manipulated and nestling growth was measured to test the hypothesis that pairs can regulate brood size during incubation based on current ability to rear nestlings. Natural (control) broods with one, two and three nestlings, and manipulated (experimental) broods reduced to one and increased to two and three young were monitored. Growth rates were measured based on weight, and wing, tail and tarsus lengths of natural and manipulated broods. We compared the slopes of each measure's regression lines of the nestlings of each brood size by t-test. Nestling growth of control nests was similar and relatively little associated with brood size. In broods reduced to one nestling, weight, wing and tail had greater growth rates, and in broods increased to three nestlings growth rates were lower. Weight was most, and tarsus length least influenced by brood size. In general, nestling growth of manipulated nests was inversely proportional to brood size. The results suggest that pairs with larger clutches are in better physical conditions than others. Thus, in experimental broods, pairs are over or under-loaded because feeding activities increase or decrease and these changes affect the growth rate of the nestlings. The present study suggests that egg ejection can control brood size. This behaviour is probably stimulated by physical changes in the adult birds during incubation. Keywords: nestling growth, brood manipulation, brood reduction, incubation. Tamanho da ninhada e sua importância no crescimento de filhotes de Streptoprocne biscutata (Aves: Apodidae) Resumo Muitos Apodidae, incluindo Streptoprocne biscutata (Sclater, 1866), derrubam ovos do ninho durante a incubação. Este comportamento tem sido interpretado como competição ou acidente. Este estudo apresenta evidências de que a expulsão de ovos é deliberada e que esse comportamento controla o tamanho da ninhada. Ninhos com diferentes tamanhos de prole foram manipulados para testar a hipótese de que os casais podem regular o tamanho da ninhada durante a incubação com base em suas capacidades de alimentar os filhotes. Ninhadas naturais (controle) com um, dois e três filhotes e ninhadas manipuladas (experimentais) reduzidas para um e aumentadas para dois e três filhotes foram monitoradas. Foram medidas as taxas de crescimento de massa, asa, cauda e tarso de proles naturais e manipuladas. As inclinações das retas de regressão do desenvolvimento de cada medida ao longo da idade dos filhotes de cada tamanho de ninhada foram comparadas pelo t-teste. O crescimento dos filhotes de ninhos controle foi semelhante e esteve relativamente pouco associado ao tamanho da ninhada. Nas ninhadas reduzidas para um filhote, a massa, asa e cauda apresentaram as maiores taxas de crescimento e nas ninhadas aumentadas para três filhotes ocorreram as menores taxas. A massa foi a variável mais influenciada pelos experimentos e o tarso a menos. De forma geral, o crescimento dos filhotes de ninhos manipulados foi inversamente proporcional ao tamanho da ninhada. Os resultados sugerem que os casais com mais filhotes estão em melhores condições físicas do que os outros. Por isso, nas ninhadas experimentais, a taxa de crescimento dos filhotes muda em virtude dos casais se encontrarem sub ou sobrecarregados na tarefa de alimentação. Sugere-se que o comportamento de expulsão de ovos possa ser uma forma de regular o tamanho da ninhada, o qual provavelmente é desencadeado por mudanças nas condições físicas das aves adultas durante o período de incubação. Palavras-chave: crescimento de filhotes, manipulação de ninhadas, redução de ninhadas, incubação. Pichorim, M. and Monteiro-Filho, ELA. 852 Braz

Environmental factors involved in breaching behavior of manta rays in estuarine waters

Improving our knowledge on the behavior of threatened species is essential for developing effective conservation actions. The Paranaguá Estuarine Complex (PEC), southern Brazil, is the only estuary in the world where manta rays have been observed performing breaches seasonally. The exact role of this breaching behavior and the environmental factors connected to it are unknown. Our goals were to determine the spatial distribution, and the temporal and environmental factors that influence the breaching behavior of this endangered group in a dynamic estuarine habitat for the first time. Manta rays were observed breaching in the PEC during austral summer and early autumn, when the sea surface temperature (SST) and precipitation were high. Generalized additive models revealed that the presence and frequency of the breaches were both influenced by the SST and hours of daily effort, while the breaching frequency was also influenced by the wind direction and speed, percentage of moon illumination, and year. The breaches were mainly concentrated near the mouth of a river. Likely these factors influenced not only the occurrence and behavior of manta rays, but also the distribution of their food source, potentially providing optimal conditions for foraging and reproduction. Based on the coloration pattern, it is possible that the observations were of Mobula cf. birostris. These results provide valuable insights into the breaching behavior of manta rays in estuarine waters that will assist future conservation initiatives and research on their behavioral ecology, to optimize fishery management and contribute to developing sustainable ecotourism in the PEC.</jats:p