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Smaller Eastern Olivaceous Warbler Hippolais pallida elaeica nests suffer less predation than larger ones

100%

Antonov A.

Acta Ornithologica

2004

tom 39

nr 2

The "costs of predation" hypothesis predicts that larger nests are more likely to be predated than smaller ones. However, nest size has not been found to be related to predation probability within any species. This study evaluated the "costs of predation" hypothesis in the Olivaceous Warbler during 2001-2003 in northwestern Bulgaria. Successful nests were significantly smaller and denser than those that were predated. Nest size decreased significantly during the course of the breeding season and increased with nest height. The relationship between nest size and the likelihood of predation was still significant even when the effects of laying date and nest height were controlled. Nest size was negatively related to fledging success even when only successful nests were considered. This finding is contrary to the prediction of the "sexual display" hypothesis, which states that nest size is positively related to fledging success, and suggests that nest size may signal phenotypic quality through the ability in this species to build a small but compact nest. It seems that both natural selection and sexual selection have led to the evolution of small nests in the Olivaceous Warbler. This is the most likely reason why the difference in nest-size between predated and non-predated nests was apparent, even in unmanipulated settings.

The timing of fledging and annual post-fledging survival of juvenile feral pigeons, Columba livia, in a city area [Pomerania, NW Poland]

80%

Hetmanski T.

Polish Journal of Ecology

2007

tom 55

nr 2

Research on the annual postfledging survival of young Feral Pigeons Columba livia was conducted in 1998-2001 in five breeding colonies located in the city centre of Słupsk (NW Poland, area 43 km²). Breeding pairs and their offspring were individually ringed. A total of 1016 clutches were studied, as was the fate of 809 fledglings. It was found that although fledglings were produced throughout the entire year, about 81-93% of young was leaving the nest in the period between April and September. The peak period of fledging occurred in May, August or June accordingly in successive study years. The dynamic of fledging in one year reflected the pairs’ egg laying activity occurring two months earlier. Juvenile mortality was highest during the first month after fledging and was found to be 45% of young birds. The main cause of death was hunger, as the young, inexperienced individuals were unable to compete successfully with adults for food at foraging areas. Loss of young clearly decreased with every successive month. The annual survival rate of juveniles produced in a calendar year was 30%. Almost all the juveniles surviving their first year of life joined the breeding population. Young produced in winter and spring had better survival rates than did those leaving the nest in summer, and especially, in autumn. The differences in survival rates found among the seasons of the year most likely resulted from changes in the pressure of competition for food in foraging areas.

Ograniczanie wyników

1 Acta Ornithologica

1 Polish Journal of Ecology

1 Antonov A.

1 Hetmanski T.

1 2007

1 2004

Wyniki wyszukiwania

Smaller Eastern Olivaceous Warbler Hippolais pallida elaeica nests suffer less predation than larger ones

The timing of fledging and annual post-fledging survival of juvenile feral pigeons, Columba livia, in a city area [Pomerania, NW Poland]