Food provisioning of White—tailed Tropicbird (Phaethon lepturus) chicks by their individually identified parents was studied at Cayo Luis Pena, Puerto Rico, in 1985—1986. This paper describes the pattern of this provisioning from the perspectives of both the chick receiving the food, and the individual parents delivering the food. The interval between feedings delivered by an individual adult was more variable than food payload mass (higher coefficients of variation), and there was no day—to—day relationship between the feeding interval and feed mass. Moreover, adults demonstrated the ability to lift and transport food payloads substantially larger than the mean feed mass. Energetic considerations suggest that there is strong selection for parents to decrease the feeding frequency and increase feed mass, to some limit imposed by either the limits of the parents' delivery capabilities, or the limits of the chick's food receiving (swallowing) capabilities (the volume a chick can ingest in one feeding bout). In fact, the limits of the chick's swallowing capabilities occur well before the parents' delivery limits are reached, and thereby set the feed mass at a weight and volume that is easily within the adults' lifting and transporting capabilities. The mean feed mass is viewed as reflecting a particular “target” payload mass that parents strive to collect as quickly as conditions, and their own individual foraging abilities, will allow, and is a practical compromise between the short—term interests of the chick and those of the adult. While parents are able to collect an abundance of food for their single chick, their pelagic foraging creates an intermittent, or “feast or famine” feeding situation for the chick which promotes the characteristic developmental pattern of slow growth and large fat accumulations. The developmental pattern of White—tailed Tropicbirds and other pelagic birds may be better understood by examining the temporal pattern of feeding, and thus there is a need for more comparative and experimental ecological and physiological studies focusing on patterns of food delivery and their possible effects, as well as the average rate of energy flow.

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The demography of Zenaida Doves (Zenaida aurita) was studied on Cayo del Agua, Culebra, Puerto Rico. We collected capture-recapture and reproductive success data and monitored annual changes in the density of ground nests in 1987–1993 and 2000. Models with time-specific apparent survival and constant capture rates (ϕ̂t, p̂c) and constant apparent survival and time-specific capture rates (ϕ̂c, p̂t) were equally parsimonious, with the former having 1.5 times more support from the data. Rainfall of the first six months of the year was positively related to nest density, and crab density was negatively related to nesting success and the number of doves fledged per nest. Crabs are the main predators of dove nests on Cayo del Agua. Models, parameterized with field data, were used to simulate full and reduced stochastic variation in environmental and demographic conditions, and predict annual changes in population size. High recruitment (births or births + immigrants) offset high losses (deaths + emigrants) in all instances. Our field data suggest that Zenaida Doves suffered an ecological crunch between 1989 and 1990, when weather (a hurricane followed by a drought), food availability, and nest predation interacted, lowering the number of locally fledged doves that survived the hatching year (1989–1990) and reproductive success (1990). Under severe conditions, population size and recovery mainly depended on immigration. Apparent survival returned to pre-hurricane levels between 1990 and 1991, and reproductive success was about average in 1991.Demografía de Zenaida aurita en Cayo del Agua, Culebra, Puerto RicoResumen. Estudiamos la demografía de Zenaida aurita en Cayo del Agua, Culebra, Puerto Rico. Durante 1987–1993 y 2000 colectamos datos de captura-recaptura y éxito reproductivo y seguimos los cambios anuales en la densidad de nidos localizados en el suelo. Los modelos con tasa de supervivencia aparente específica para cada período de tiempo, y tasa de captura constante (ϕ̂t, p̂c), y con tasas de supervivencia aparente constante y captura específica para cada período de tiempo (ϕ̂c, p̂t) tuvieron igual parsimonia, aunque el primer modelo fue apoyado por los datos 1.5 veces más que el segundo modelo. La lluvia de los primeros seis meses del año se relacionó positivamente con la densidad de los nidos, y la densidad de los cangrejos se relacionó negativamente con el éxito de nidificación y el número de individuos producidos por nido. Los cangrejos son los principales depredadores de los nidos de Z. aurita en Cayo del Agua. Usamos modelos, con estimados de parámetros basados en los datos de campo, para simular diferentes niveles de variación estocástica en las condiciones ambientales y demográficas, y para predecir cambios anuales en el tamaño poblacional. El reclutamiento (nacimientos o nacimientos + inmigrantes) superó a la pérdida (muertes + emigrantes) de individuos en todo momento. Nuestros datos de campo sugieren que Z. aurita sufrió un gran impacto ecológico entre 1989 y 1990, cuando las condiciones climáticas (un huracán seguido de una sequía), la disponibilidad de alimento, y la depredación de nidos interactuaron, disminuyendo el número de individuos que sobrevivieron el primer año de vida (1989–1990) y el éxito reproductivo (1990). Bajo condiciones severas, el tamaño de la población y su recuperación dependió mayormente de la inmigración. La supervivencia aparente regresó al mismo nivel que antes del huracán entre 1990 y 1991, y el éxito reproductivo se acercó a un nivel promedio en 1991.