Resumo
The nesting success of three colonies of Streptoprocne biscutata (Sclater, 1866), and the influence of clutch and brood size on nesting success of species were studied. Overall, apparent nesting success was 58% and Mayfield nesting success was 53%. Nest survival during incubation (64%) was lower than during the nestling period (83%). During incubation, clutches were lost to rain, desertion, predation, egg ejection, egg damage, and egg disappearance. During the nestling period, losses occurred due to offspring disappearance, nestling death by starvation, predation and falling. During both incubation and nestling periods, predation was low, while egg ejections and nestling starvation were the main causes of nest failure. Nest survival during incubation was directly proportional to clutch size, while during the nestling period it was inversely proportional to the brood size. Apparently, there seemed to be an advantage to having more eggs during incubation. However, if all eggs were to hatch during unfavorable weather the nest success could be low. These results suggest that when the breeding pairs face adversity during incubation, they control the brood size by ejecting part of the clutch.
Resumo
The nesting success of three colonies of Streptoprocne biscutata (Sclater, 1866), and the influence of clutch and brood size on nesting success of species were studied. Overall, apparent nesting success was 58% and Mayfield nesting success was 53%. Nest survival during incubation (64%) was lower than during the nestling period (83%). During incubation, clutches were lost to rain, desertion, predation, egg ejection, egg damage, and egg disappearance. During the nestling period, losses occurred due to offspring disappearance, nestling death by starvation, predation and falling. During both incubation and nestling periods, predation was low, while egg ejections and nestling starvation were the main causes of nest failure. Nest survival during incubation was directly proportional to clutch size, while during the nestling period it was inversely proportional to the brood size. Apparently, there seemed to be an advantage to having more eggs during incubation. However, if all eggs were to hatch during unfavorable weather the nest success could be low. These results suggest that when the breeding pairs face adversity during incubation, they control the brood size by ejecting part of the clutch.
Resumo
The nesting success of three colonies of Streptoprocne biscutata (Sclater, 1866), and the influence of clutch and brood size on nesting success of species were studied. Overall, apparent nesting success was 58% and Mayfield nesting success was 53%. Nest survival during incubation (64%) was lower than during the nestling period (83%). During incubation, clutches were lost to rain, desertion, predation, egg ejection, egg damage, and egg disappearance. During the nestling period, losses occurred due to offspring disappearance, nestling death by starvation, predation and falling. During both incubation and nestling periods, predation was low, while egg ejections and nestling starvation were the main causes of nest failure. Nest survival during incubation was directly proportional to clutch size, while during the nestling period it was inversely proportional to the brood size. Apparently, there seemed to be an advantage to having more eggs during incubation. However, if all eggs were to hatch during unfavorable weather the nest success could be low. These results suggest that when the breeding pairs face adversity during incubation, they control the brood size by ejecting part of the clutch.
Resumo
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.
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.