JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Animal Ecology. Summary 1. The hypothesis that late breeding entails reproductive costs to birds was tested by comparing breeding traits of control and delayed great tit Parus major clutches. 2. In our study area, great tits and house sparrows Passer domesticus compete for nesting boxes. Since early March, nesting boxes were checked twice a week and initiated sparrow nests removed, to allow great tits to breed. 'Delayed' great tit pairs were those which, having a territory, had the nesting where they eventually bred occupied by sparrows, and therefore did not start laying until these abandoned the nesting box. Delayed pairs were assumed to be a random sample of the population. Age composition (1-year vs. older birds) and tarsus length did not differ between control and delayed birds. 3. In 1990-92, a total of 40 pairs had their breeding delayed, while 56 acted as controls. The mean laying date of delayed pairs was at least 10 days later than controls. 4. Delayed first clutches were smaller and took longer to hatch than controls, but mean egg volume did not differ between them. Fledging success was lower in delayed nests. Young from delayed broods were lighter at day 15 and reached a lower asymptotic weight. The mean growth rate of the nestlings was negatively related to clutch size, and differed between years, but did not differ between control and delayed broods. 5. Control pairs were more likely to produce a second clutch, if the first one succeeded, or a replacement clutch, if the first one failed, than delayed pairs. The total production of fledglings per pair per season was higher in control pairs. Control pairs were more likely to recruit at least one young into the local breeding population than delayed pairs. However, it is not known whether late fledglings dispersed further. 6. Our results show that delayed pairs produced fewer fledglings, of lower quality, and were less likely to recruit them into the local breeding population than controls. Therefore, the causal relationship between poor breeding performance and late breeding is supported.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.

Plastic intake by marine vertebrates has been widely reported, but information about its presence in continental waterfowl is scarce. Here we analyzed faeces of waterbirds species (European coot, Fulica atra, mallard, Anas platyrhynchos and shelduck, Tadorna tadorna) for plastic debris in five wetlands in Central Spain. We collected 89 faeces of shelduck distributed in four lakes, 43.8% of them presented plastic remnants. Sixty percent of 10 faeces of European coot and 45% of 40 faeces of mallard contained plastic debris. Plastic debris found was of two types, threads and fragments, and were identified as remnants of plastic objects used in agricultural fields surrounding the lakes. Differences in prevalence of plastic in faeces, number of plastic pieces per excrement and size of the plastic pieces were not statistically significant between waterfowl species. Thus, our results suggest that plastic may also be frequently ingested by waterfowl in continental waters, at least in our study area. Future studies should address this potential problem for waterbird conservation in other wetlands to evaluate the real impact of this pollutant on waterbirds living in inland water.