Although the costs of parental care are at the foundations of optimal-parental-investment theory, our understanding ofthe nature of the underlying costs is limited by the difficulty of measuring variation in foraging effort. We simultaneously measured parental provisioning and foraging behavior in a free-living population of Zebra Finches (Taeniopygia guttata) using an electronic monitoring system. We fitted 145 adults with a passive transponder tag and remotely recorded their visits to nest boxes and feeders continuously over a 2-month period. After validating the accuracy of this monitoring system, we studied how provisioning and foraging activities varied through time (day and breeding cycle) and influenced the benefits (food received by the offspring) and costs (interclutch interval) of parental care. The provisioning rates of wild Zebra Finches were surprisingly low, with an average of only one visit per hour throughout the day. This was significantly lower than those reported for this model species in captivity and for most other passerines in the wild. Nest visitation rate only partially explained the amount of food received by the young, with parental foraging activity, including the minimum distance covered on foraging trips, being better predictors. Parents that sustained higher foraging activity and covered more distance during the first breeding attempt took longer to renest. These results demonstrate that in some species matching foraging activity with offspring provisioning may provide a better estimate ofthe true investment that individuals commit to a reproductive attempt. Uso de un Sistema de Monitoreo Electrónico para Conectar el Aprovisionamiento de las Crías y el Comportamiento de Forrajeo en un Ave Paserina SilvestreRESUMEN.-Aunque los costos del cuidado parental hacen parte de la base de la teoría sobre inversión parental óptima, nuestro conocimiento sobre los costos subyacentes está limitado por la dificultad de medir la variación en el esfuerzo de forrajeo. En este estudio medimos simultáneamente el aprovisionamiento de las crias y el comportamiento de forrajeo en una población de vida libre de Taeniopygia guttata empleando un sistema electrónico de monitoreo. Ajustamos transponedores pasivos en 145 adultos y registramos sus visitas a cajas de anidación y comederos de forma continua a lo largo de dos meses. Después de validar la exactitud de este sistema de monitoreo, estudiamos cómo variaban las actividades de aprovisionamiento y alimentación en el tiempo (en el dia y en el ciclo anual) y cómo influenciaban los beneficios (alimento recibido por las crías) y los costos (intervalo entre posturas) del cuidado parental. Las tasas de aprovisionamiento fueron sorpresivamente bajas, con un promedio de sólo una visita por hora a lo largo del día. Esto fue significativamente más bajo que lo que se había documentado para esta especie modelo en cautiverio y para la mayoría de otras aves paserinas en el campo. La tasa de visitas a los nidos sólo explicó parcialmente la cantidad de alimento recibida p...

No abstract

Reproduction in opportunistically breeding bird species has traditionally been considered non-seasonal with individuals taking advantage of favourable environmental conditions as they arise. However, some studies imply that this opportunistic breeding may be superimposed on an underlying seasonality, which has effects on the readiness to breed when conditions are favourable. The zebra finch (Taeniopygia guttata) is the classic opportunistic breeder and widely used as such in studies. In a series of laboratory-based breeding experiments, we found evidence to suggest that there are seasonal differences in maternal reproductive investment in the zebra finch even when photoperiod, temperature, relative humidity and diet were held constant. Females showed highly significant seasonal differences in clutch size and egg mass with laying order. Clutch size showed a spring/summer peak typical of multi-brooded species in the wild. There was also a significant increase in egg mass with laying order in all seasons except winter. This variation in breeding parameters with season may allow females to adjust investment depending on the potential fitness returns from a given reproductive attempt. These findings also raise a warning about interpreting results of multiple zebra finch breeding experiments that have been carried out in different seasons.

Zebra finches have played a central role in the discovery of a variety of maternal effects over the past decade, with females shown to adjust resource allocation to their eggs in response to variables such as the appearance of their partner, their own condition, and the diet on which they are maintained. In addition to being the focus of some of the most high profile individual studies that have influenced maternal effects research in birds, the multitude of zebra finch studies together provide the most comprehensive set of data to illuminate general patterns and compare different maternally derived variables. Surprisingly, to date, virtually all of this work has focused on captive populations of the zebra finch that have been domesticated for many generations, and which are typically held under relatively constant environmental and dietary conditions. Here we report the first data on resource allocation across the egg laying sequence in a free-living wild population. Reassuringly we find that the patterns that have been found in the majority of studies of domesticated populations with respect to investment across the laying sequence were all present in the wild population. The size and mass of eggs increased through the laying sequence whilst the concentration of carotenoids significantly decreased across the laying sequence. Although there was no significant pattern with respect to testosterone across the laying sequence the first two eggs had a higher level of testosterone than the last few eggs in the clutch, which is also consistent with the findings of earlier studies in captive populations. Reassuringly we find that the patterns that have been found in the majority of studies of domesticated populations with respect to investment across the laying sequence were all present in the wild population. The size and mass of eggs increased through the laying sequence whilst the concentration of carotenoids significantly decreased 45 across the laying sequence. Although there was no significant pattern with respect to testosterone across the laying sequence the first two eggs had a higher level of testosterone than the last few eggs in the clutch, which is also consistent with the findings of earlier studies in captive populations.