Larus cachinnans

(last update: February 16, 2013)

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adult cachinnans: January

Below we add a copy of the paper by Neubauer et al. in Vogelwelt.

Breeding large gulls in Poland: distribution, numbers, trends and hybridisation.

BY: Neubauer, G., M. Zagalska-Neuhauer, R. Gwiazda, M. Faber, D. Bukaciriski, J. Betleja & R Chylarecki
IN: Vogelwelt 2006-127: 11-22.

Abstract

The current situation of three species of large gulls (L. argentatus, L. cachinnans and L. michahellis) in Poland is presented based on results of own studies and published data. Herring Gulls started to breed in the country in the late 1960s and rapidly increased in numbers until the early 1990s. This exponentially increasing population trend, coupled with southward expansion and colonisation of inland areas of N Poland has been recently reverted, with the population estimated at 1,200-1,500 pairs in the early 2000s, down from some 1,900-2,000 a decade ago. The increase of Caspian Gull in southern Poland is exponential and very fast with an annual growth rate of 33% between 1997 and 2004; the population reached 480 pairs in 2004. The Yellow-legged Gull remains a rare breeder and its population probably does not exceed 5-10 pairs.

Hybridisation occurs mainly between the commonest species, Herring Gull and Caspian Gull, and is caused primarily by an apparently random pairing in mixed colonies in central Poland. The high frequency of mixed pairs (c. 60% and c. 40% respectively) and a high share of hybrids were recorded at two sites in the Vistula river valley: the middle Vistula and the Wloclawek Reservoir. The situation of particular breeding colonies in southern and central Poland seems to be unstable, which favours the exchange of individuals between these breeding places. Frequent dispersal along a north-south axis also favours hybridisation.

Fig. 1: Distribution of breeding Herring Gulls (blue dots), Caspian Gulls (red dots) and Yellow-legged Gulls (green dots) in Poland, 1995-2004. Grey: breeding site of unknown species or mixed colony. Large symbols: colonies > 100 bp; small symbols: < 100 bp. Orange lines show Wloclawek Reservoir colony (1) and areas defined in the text as ‘middle Vistula’ (area 2) and ‘southern Poland’ (3-6). Remaining marked colonies mentioned in the text are: 3 = Tarnow, 4 = Jankowice, 5 = Goczalkowice Reservoir, 6 = Czorsztyn Reservoir and 7 = Mietkow Reservoir.

1. Introduction

Expansion of large gulls from the Larus argentatus-cachinnans-michahellis complex in Europe is observed from the beginning of the 20th century and lasts with some fluctuations until now (HAFFER 1982; DEVILLERS 1983; SNOW & PERRINS 1998; BIRDLIFE INTERNATIONAL 2000). The first coastal breeding site of northern Herring Gull L. a. argentatus in Poland was recorded in the late 1960s (BEDNORZ 1971). Scarce inland breeding sites on the lakes were established in the late 1970s; since the early 1980s, the main axis of expansion from the north was the Vistula River (TOMIALOJC 1990), where most of the inland population breeds until now.
Caspian Gulls L. cachinnans or Yellow-legged Gulls L. michahellis or both, colonised the middle section of Vistula first, coming from the south and south-east probably in the early 1980s (WESOLOWSKI et al. 1984; BUKACINSKI et al. 1989). During the 1990s, Caspian Gull has spread to most of southern Poland with several known colonies (FABER et al. 2001; TOMIALOJC & STAWARCZYK 2003).
Yellow-legged Gull distribution is poorly known and this taxon is the rarest among the three, with just a few breeding localities mainly in southern Poland (POLA et al. 1998; FABER et al. 2001). Rapid expansion of - especially - Herring and Caspian Gulls caused that a secondary contact zone formed on the Polish lowland, between earlier separated northern (argentatus) and southern (cachinnans and michahellis) taxa of large gulls. The contact zone has remained unexplored for years. However, the last seasons brought much new evidence and information about the large gull complex allowing a more detailed analysis of the Polish contact zone. The main aim of this paper is to present the most updated information on distribution, numbers and trends of all three taxa and to provide basic data on the frequency of their hybridisation in Poland.

Location 1: Śluza na tamie we Włocławku (52°39`N, 19°08`E). Picture: Jan Wende. Click image to see more pictures of Wloclawek colony and scenery.

Location 2: Nadwiślański pejzaż, Kozienice - Dęblin (approx.: 51°35’N, 21°40'E,). Picture: Infobart. Click image to see more pictures of Wisła River and scenery.

2. Methods

Data on distribution and numbers presented in this paper include: 1. complete evidence on breeding records of large gulls in Poland since they started to breed, and 2. recent (2002-2004) data on numbers from surveying their breeding colonies. Studies on hybridisation and population structure were conducted in 2002-04 at Wloclawek Reservoir (52°39`N, 19°08`E, Fig. 1: locality 1), in 1995-2004 at the middle Vistula between Deblin and Kozienice power station (393-423 km of the river stream, central point approx.: 51°35’N, 21°40'E, Fig. 1: area 2), in 1999-2004 in Tarnow (50°01’N, 20°59’E) and Jankowice (50°01’N, 19°26’E, Fig. 1; localities 3 and 4, respectively). Fewer breeding gulls were trapped in Goczaikowice Reservoir and Czorsztyn Reservoir (in 1999-2004, Fig. 1: localities 5 and 6, respectively).
Adult gulls were trapped on the nests, measured, ringed and released. Complete morphological documentation, including the basic measurements, wing-tip pattern characteristics and the colouration of bare parts, was taken from most of the birds. Altogether, 177 birds were trapped in Wloclawek, 85 at the middle Vistula and 204 in the region of ‘southem Poland’ (i.e. 60 in Tarnow, 139 in Jankowice, two on Goczalkowice Reservoir and three on Czorsztyn Reservoir). In addition, visual observations in each mentioned locality were used to assign pairs to species.

Identification of each bird was based on a number of important characters, including the colouration of bare parts, wing-tip pattern and “to a lesser degree” basic measurements. As a main reference we used morphological data collected in the same way within the breeding ranges of ‘pure’ (allopatric) species: Molochnyy Lyman, Azov Sea, S Ukraine, 46°35’N, 35°21'E (for cachinnans), Saline di Comacchio, NE Italy, 44°40’N, 12°12’E (for michahellis) and Gdynia, N Poland, 54°31`N, 18°33’E (for argentatus) (ZAGALSKA-NEUBAUER & NEUBAUER, unpublished). Data from the literature were also included (i. e. BARTH 1968;
ISENMANN 1973; HAFFER 1982; DEVILLLERS 1983; MlERAUSKAS et al. 1991; LIEBERS & DIERSCHKE 1997; MALLING OLSEN & LARSS0N 2003).

All the birds showing any of the features (a) falling outside the range of variation known from the literature and/or from our reference samples, (b) with intermediate characters, or (c) with part of characters associated with one species and the remaining associated with another was defined as ‘hybrid’. All three species show large variability and we can expect that some individuals classified as pure species can represent in fact backcross hybrids, inseparable from parental species by morphology alone (RANDLER 2002, 2004). Therefore, the actual proportion of hybrids and degree of hybridisation in Polish populations of large gulls can be underestimated. More detailed results on morphological variability of the mid-Polish population will be presented elsewhere (CHYLARECKI et al., in prep.).
A hybrid (or mixed) pair is defined as a pair, which includes at least one hybrid individual or two birds of pure, but different taxa (i. e. Herring x Caspian Gull). A hybrid zone is defined as the area with colonies, where mixing between large gulls occurs regularly to a significant degree.

Tarnow (50°01’N, 20°59’E). Important feeding area for Caspian Gulls: fishponds / Stawy rybne near Tarnow (see PDF). Picture: Piotr Skorka.

Looking east to west over river Wisła near Jankowice, the village in the background (50°01’N, 19°26’E) with its reservoir. Picture: Czary.

END OF PART 1
CONTINUE PART 2: RESULTS

Larus cachinnans adult 006P January 12 2007 & January 06 2008, Woerth, Niederoesterreich, Austria. Picture: Wolfgang Schweighofer.

Originally from Azov Sea, Ukraine.