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Hybridization of the Mediterranean Gull Ichthyeatus melanocephalus in Poland

Zagalska-Neubauer Magdalena, Chodkiewicz Tomasz, Iciek Tomasz, Neubauer Grzegorz, Zieliński Piotr

Polish Journal of Ecology

2022

vol. 70, nr 4

175--184

Hybridization, the interbreeding of individuals from different taxa, is usually the result of contact between closely related species. It occurs when reproductive barriers between species are not fully developed during speciation. Gulls are a classic example of hybridization in birds. However, the group of so-called “small gulls” is poorly recognized in this context. Here, we summarised data on Mediterranean gulls Ichthyeatus melanocephalus hybridization documented in Poland for the 2006–2022 period. In the mid-20th century, this species began successfully colonising many European countries, and the first documented breeding pair of Mediterranean gull was recorded in Poland in 1981. The first documented cross-breeding between a male Mediterranean gull and a female black-headed gull Chroicocephalus ridibundus was recorded in Poland in 2006. Since then, a total of 25 interspecific pairs, between Mediterranean gulls and black-headed gull or common gull Larus canus, have been observed. Interspecific pairs with black-headed gull were the most numerous (76%). However, mixed pairs – formed by one of parental species and individual of the Mediterranean gull hybrid – were the most common pair category (N = 60). Neither pairs consisting of two hybrids individuals nor of Mediterranean gulls × common gull hybrids have been recorded in the colonies. The number of Mediterranean gulls fluctuated between 50 and 100 pairs during studied period. The number of interspecific breeding pairs remained constant over a 17-year period, one to three pairs per breeding season, while the number of mixed breeding pairs has increased over time and reached maximum 9 pairs per season. Overall, there is a clear increase in the proportion of mixed and interspecific broods in relation to the number of pairs consisting of two ‘pure’ Mediterranean gulls, such pairs approached 38% in 2019.

Egg Losses Caused by Cold Snap in the Black-Headed Gull, Chroicocephalus ridibundus L.

Indykiewicz P.

Polish Journal of Ecology

2015

Vol. 63, nr 3

460--466

Short- and medium-distance migrant birds that return to the breeding grounds early can usually take better-quality territory leading to higher breeding success than of congeners arriving later. On the other hand, early breeders usually have to face severe weather conditions. 109 Black-headed Gulls which had begun laying in a breeding colony (N-Poland) earlier than the remaining 960 females lost 66.2% of eggs because of severely adverse weather. On 9 April 2012 ambient temperature fell to -4.6°C during the first two hours after sunrise (06:00–07:59) resulting in eggs cracking during the adults' first feeding bout after the night. Up to 1 mm wide cracks in eggshells were from 3 mm to 24 mm long; in some eggs the external shell membrane also broke. Pairs that lost eggs did not repeat broods. In this way in 2012 this colony suffered the greatest loss of eggs during its 15-years history. This event showed that even in the temperate climate, adverse weather, a consequence of the global climate change, does have negative impact on life history traits of birds.