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2 Polish Journal of Ecology

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Parental provisioning in response to natural variation of brood size in the Black-billed magpie (Pica pica L.) : video analysis of behaviors in the nests

Lee S., Jabłoński P., Choe J., Choi J.

Polish Journal of Ecology

2010

Vol. 58, nr 3

553-562

Natural selection will favor parents who adjust their effort in relation to the fitness costs and benefits from the current brood. In this study, we investigated how magpie parents adjust provisioning effort based on the number of nestlings in the brood, by analyzing video recordings of begging and feeding behaviors of birds. The number of visits per hour increased with brood size, but the number of feeding events per visit did not. Because of the latter, parental provisioning that a nestling is receiving on average decreased in larger broods. This may be viewed either as an evidence for the limitation of parental provisioning in larger broods, or as an evidence of parental strategy optimizing the brood-size-specific provisioning effort for the current reproductive event as a tradeoff between current and future reproduction. With other aspects of parental provisioning behavior, we did not find clear indication that parent confronts upper limitation in provisioning large broods. Pervisit number of feeding and nestlings. body condition around the time of fledging did not depend on brood size, which implies that parental effort is not at its limit in larger broods. Based on the results, we suggest that the provisioning effort of black-billed magpie parents is better explained by the life-history trade-off model for provisioning.

Impact of local air temperatures on the brood size in starling (Sturnus vulgaris L.)

Dolenec Z.

Polish Journal of Ecology

2009

Vol. 57, nr 4

817-802

Many papers over recent years have demonstrated long-term temporal trends in biological parameters that can only be explained by global warming. I examined the long-term trends in the brood size of Starling (Sturnus vulgaris) in Mokrice area (north-western Croatia). I collected data from 1977 to 2007. To investigate the effect of spring temperatures on the brood size, local air temperature was used. The significant correlation (P <0.01) between mean brood size and the year (y = -31.403 + 0.018x) indicates that brood size (mean number of nestlings per nest) increased by 0.018 nestling per year, or 0.54 nestling over the period of the study. Correlation between brood size (mean number of nestlings per nest) and mean spring temperature was also significant (P <0.05) and regression equation (y = 4.162 + 0.07x) indicates that brood size increased by 0.07 nestling per 1[degrees]C. The correlation between mean spring air temperature and research year was significant (P <0.01). This data show that the mean May temperature has been increasing in the study area. We can conclude that Starlings in north-western Croatia are increasing their brood size and that the most likely cause is a long-term increase in spring temperatures.