Wyniki wyszukiwania - BazTech

1

Central-place foraging in an urban landscape : body mass of common voles (Microtus arvalis Pall.) caught by breeding Kestrels (Falco tinnunculus L.) is positively correlated with availability of hunting sites

Kubacka J., Żmihorski M., Mirski P., Rejt Ł.

Polish Journal of Ecology

|

2010

|

Vol. 58, nr 2

387-391

EN

In the reproduction period a male Kestrel (Falco tinnunculus) is a centralplace forager, i.e. it transports food from hunting grounds to a central location - the nest. A centralplace forager is predicted to take larger or more prey when distance to a foraging site is longer. We studied kestrels breeding in a large Central European city (population 1.7 million), whose main prey are common voles (Microtus arvalis). Kestrel nests are located in the centre and the outskirts, although common voles are scarce in the former. The aim of our study was to analyse the body mass of common voles found in pellets under kestrel nests and relate it to the availability of common vole habitats within 1 km from the nests, controlled for vole frequency in the pellets. We assumed that the greater availability of common vole habitats, the shorter the distance to a foraging site. We found that the body mass of common voles found in pellets was significantly positively correlated with the availability of their habitats, but was not affected by their frequency in pellets. Our results may indicate that, contrary to the central-place foraging rule, and irrespectively of the amount of other prey taken, the kestrels hunted smaller voles when foraging grounds were further away. This might stem from decreased selectivity caused by competition, either in the native territory (due to the high density of kestrels in the centre) or in territories of outskirt kestrels, invaded by city centre kestrels. On the other hand, due to lack of data on the body size of common voles in our study area, the results may suggest that common voles were on average smaller in the centre than in the outskirts. Although the published data do not support the second explanation, more research is needed to verify this.

2

Forest fragment size affects edge effect in nest predation . experiment with artificial nests

Mazgajski T., Rejt Ł.

Polish Journal of Ecology

|

2005

|

Vol. 53, nr 2

233-242

EN

Many species react negatively to forest fragmentation. If this process also decreases the abundance of forest predators we expect that birds. broods in small forest patches would be preyed upon only by predators that penetrate from the matrix while broods in larger patches would be also attacked by predators specifically associated with forests. We tested the hypothesis that an increase in forest patch size leads to an increase in predator pressure on nests. Studies were conducted in Central Poland, in an agriculturally dominant area with 6% forest cover and highly fragmented woodlot. Three patch sizes were chosen for the experiment: small (< 20 ha), medium (30 - 50 ha) and large (> 120 ha). One quail egg was placed in each nest. All transects were checked after 13 - 14 days. The highest predation level was found in medium-sized patches, the lowest . in the largest patches. We found a reverse edge effect on nest predation in the largest patches, i.e. a decreased predation risk closer to the forest/matrix border. When comparing our results with other studies, it seems that the manner of classifying forest size significantly affects the results obtained. This may explain the differences in the results of many authors studying this phenomenon.

3

Does egg sex ratio in Urban Kkestrels (Falco tinnunculus) differ from parity?

Rejt Ł., Gryczyńska-Siemiątkowska A., Rutkowski R., Malewska A.

Polish Journal of Ecology

|

2005

|

Vol. 53, nr 4

545-552

EN

Paper tests the hypothesis that urban kestrels (Falco tinnunculus) are sex biased connected with urbanization gradient (central zone vs suburbs), laying date and level of PCB-contamination. Blood samples of 158 nestlings were collected on FTA cards. Sex of nestlings was determined using a multiplex PCR technique. Egg sex ratio among kestrels in Warsaw (Poland) was 51% and did not differ significantly from parity (n = 34 nests). Among broods at the beginning and at the end of the breeding season proportion of males was significantly higher than in the middle of the season. Sex ratio was significantly different along the urbanization gradient. Proportion of males in broods at the central zone reached only 44% contrary to the external zone where males composed 65% of chicks. Possibly influence of laying date, female condition as well as population size and isolation is discussed. For assessing the level of PCBs small amount of blood (approximately 1 mm3) was collected from the brachial vein from 83 individuals (17 nests). All samples from a particular nest were pooled together to increase the possibility of successful analysis. Among most broods (pooled data for nests with complete and partial hatching) contamination of PCBs in nestlings. blood was low (average level of PCBs was 55.1 ppm, range: 0-252.8). A trend toward decreasing proportion of males among broods with higher PCB-contamination was found to be insignificant. Probably level of organic contamination in chicks. blood depends more on pollution existing in rural hunting areas and is not directly connected with nest site and its close vicinity.

4

Nocturnal feeding of young by urban Peregrine Falcons (Falco peregrinus) in Warsaw (Poland)

Rejt Ł.

Polish Journal of Ecology

|

2004

|

Vol. 52, nr 1

63-68

EN

In 2000 and 2002, the same pair of Peregrine Falcons occupied a nest box situated on the highest building within the Warsaw city centre. The nest box was monitored with a video camera and an infrared lamp. Records collected between 20:00 and 4:00 (DST) during the nestling stage (after the first chick hatching to fledging the last one) were used for analysis. Data from 34 nights in 2000 and 21 nights in 2002 were analysed. The majority of night feedings of nestlings was performed between 00:00 and 04:00. The average frequency of feedings was 1.5 events per night. It shows that night feedings can be considered an important part of feeding pattern during nestling period.