Creation and development of the subcolony in Cormorant Phalacrocorax carbo sinensis at the Jeziorsko reservoir, Central Poland
2010
Minias, Piotr | Kaczmarek, Krzysztof | Janiszewski, Tomasz
The research was conducted at Jeziorsko reservoir (51°73'N, 18°63'E) in Central Poland during the years 2004-2007. In 2005, a small subcolony of Cormorants (41 breeding pairs) was created about 1 km away from the main colony (370 breeding pairs). This year, the mean clutch size in the subcolony was lower than in the main colony and the fraction of small clutches (2-3 eggs) in the subcolony was significantly higher (57.1% vs. 37.1%). Although in 2005 breeding success was unusually low in the main colony, the number of fledglings raised per nest and per successful nest were significantly higher in the main colony in comparison to the subcolony. This followed the higher losses of whole clutches/broods recorded in the subcolony (68.6% vs. 39.5%). In the following year (2006), the number of pairs breeding in the subcolony increased over 4-fold (165 pairs) and was only slightly lower than in the main colony (220 pairs). The values of all breeding parameters recorded in the subcolony were significantly higher than in the previous year and were similar to those in the main colony. In 2007 the number of fledglings raised per successful nest in the subcolony was significantly higher in comparison to the main colony. The obtained results suggest that probably young and inexperienced birds limited by the availability of the nest sites were mainly involved in the creation of the subcolony. The growth of the breeding parameters recorded in consecutive years in the subcolony could be connected with the subsequent movement of higher-quality birds from the main colony and shows the advantages of occasional abandonment of overexploited colony location.
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