ZOBODAT - www.zobodat.at Zoologisch-Botanische Datenbank/Zoological-Botanical Database Digitale Literatur/Digital Literature Zeitschrift/Journal: Seevögel - Zeitschrift des Vereins Jordsand zum Schutz der Seevögel und der Natur e.V. Jahr/Year: 1991 Band/Volume: 12_2_1991 Autor(en)/Author(s): Mierauskas Pranas, Buzun Valerie Artikel/Article: Competitive Interactions between the Herring Gull L. a. cachinnans and the Great Black-Headed Gull L. ichthyaetus at Sivash Lake (South Ukraine) 34- 35 34 Competitive Interactions between Herring Gull and Great Black-Headed Gull Competitive Interactions between the Herring GullL. a. cachinnans and the Great Black-Headed Gull L. ichthyaetus at Sivash Lake (South Ukraine) From Pranas Mierauskas and Valerie Buzun Introduction peak in the first half of April. L. ichthyaetus ready settled. However, this was the sole means for L. ichthyaetus to deter aggres­ At Lake Sivash, as in many European laid eggs from mid-March to the end of the countries and North America, the Herring month, the egg-laying of the whole colony sive attacks of L. a. cachinnans and to oc­ Gull Larus a. cachinnans constantly in­ was over in the period of 10 to 12 days cupy the territory. Colonies ofL. ichthy­ (Kostin 1983, Siochin et al. 1988). Chicks were dense, pairs of this species creases in number, expands its breeding aetus usually nested in 17,5 ±2,5 cm intervals territory and occupies new habitats (Sio- of L. ichthyaetus hatched in mid-April in the interval of 7 to 10 days. After hatching, from each other in the centre and in 1 m in­ chin et al. 1988). In the Great Black-head­ ed Gull Larus ichthyaetus, these proces­ when chicks were already able to walk, tervals at the periphery (Siochin et al. they used to form a kind of flocks which 1988). ses occur less intensively. These two spe­ cies form mixed colonies, their feeding ra­ were gradually joined by all the young. In the period of egg-laying and hatching tions are similar, but they differ in percen­ Thus all birds of the species laid eggs or Herring Gulls often attacked the nests of tage composition of feeding objects (Sio- hatched in a strictly determined period of Great Black-headed Gulls, especially, time. Egg-laying and hatching were timed chin et al. 1988). Competition for feeding those at the periphery of the colony and sites in the colony, for feeding objects, as so that these processes never overlaid, those left by their owners. Neighbours of well as strong inclination for predation in i. e. hatching started only when egg-laying the attacked nest did not chase away the L.a. cachinnans determine agressive re­ process in the colony was over. Such tim­ intruder trying only to frighten it by jabbing ing is also characteristic of lationships between the species in the co­ Larus melano- posture. Nimbleness of L.a. cachinnans lony. cephalus and Larus atricilla in North Ame­ allowed them to avoid the jab. L. ichthy­ rica (B urger 1979; B uzun & M ierauskas aetus left the nest only then the distance Study area and methods 1987). between the approaching man and the The processes of egg-laying and hatching nest was 4-5 m. The moment L. ichthy­ Investigations were carried out in Central in the Herring Gull were not strictly limited aetus left the nest,L. a. cachinnans start­ Sivash (the island of Kitai) in April of 1984 in time, i.e. when some birds were begin­ ed eating eggs even in the presence of the and 1985, also in Eastern Sivash (near the ning to lay eggs, other clutches were al­ man. When L.a. cachinnans were ap­ island of Kujanly) in the first part of May in ready hatching. Thus the physiological proaching of flying above L. ichthyaetus, 1986. The Kitai is an island of solid ground state of Herring Gulls is more diverse than the latter used to turn their heads towards (mainly clay) covered by dense grass ve­ that of Great Black-headed Gulls, what, the predators with their bills open. To de­ getation reaching above 50 cm height, the most probably, determines the aggressive fend from the intruder L. ichthyaetus jab­ area of the island being 3 ha and the behaviour of Herring Gulls. bed it with the bill or, if the predator seem­ height of banks 6m. In Eastern Sivash L.a. cachinnans arrived at the breeding ed persistant, left the nest and chased the near the Kujanly there are some small al­ intruder away beeting it with wings or luvial sandy islands with the admixture of territory and began making nests earlier shells. L. ichthyaetus bred in one about than L. ichthyaetus but these were only 150 m length and to 20 m width. There solitary individuals (Kostin 1983; Siochin were 4 microcolonies there (with 40-60et al. 1988). L. ichthyaetus began making nests each) of 5 to 8 m apart. In total, 200 their nests after the territory had already pairs bred in the island. been occupied by solitary L.a. cachin­ nans. L. ichthyaetus were characterized In the space between the colonies of by mass colonization of the territory; it also L. ichthyaetus, L. a. cachinnans and applies to L. melanocephalus (B uzun & Phalacrocorax carbo bred. The island of Mierauskas 1987). Such an entire occu­ Kitai concentrated 2 microcolonies, locat­ pation of the territory evoked aggressive ed in a distance of 3-4 m each from reaction of L. a. cachinnans that had al­ another. Observations were completed using a small tent located not far from the colo­ nies. Behaviour of both species have been observed visually, filmed and photo­ graphed. Vocalizations were taped on a Sony TC-800B tape recorder. Some birds were marked by picric acid without catch­ ing them (e. g. dyeing the walls of the nest, etc.). Results Fig. 1: The Great Black-headed Gull sitting in its nest is often attacked by groups of the Occupation of breeding areas occurred Herring Gulls which increase their success in oophagia while cooperating among from mid-February to early March (Kostin 1983). L. ichthyaetus began making their themselves. nests in places without or with thin grass Abb. 1: Eine auf ihrem Nest sitzende Fischmöwe(L. ichthyaetus) wird häufig von mehre­ vegetation. Egg-laying of L.a. cachinnans ren Silbermöwen(L.a. cachinnans) attackiert. Durch Kooperation mehrerer started on March 5-18 and reached the dieser Möwen erhöhen sie ihren Erfolg beim Eierraub. SEEVÖGEL, Zeitschrift Verein Jordsand, Hamburg 1991 / Band 12, Heft 2 35 creases considerably, thus a newly form­ ed group colonizes a new area. Solitary new-comers would undoubtedly be pushed out by L. a. cachinnans. Acknowledgements We are grateful to Dr. Prüter for encourage­ ment to publish this article in »Seevögel«. We thank Mr. E.G reimas , Mr. G.V aitkus and Mr. M. Zurba for assistance with the field work, Mrs. V.Z aliene helped with translations. Zusammenfassung Konkurrenzbeziehungen zwischen der Silbermöwe (La. cachinnans) und der Fischmöwe (L. ichthyaetus) am Sivash Fig.2: The Great Black-headed Gull’s clipping is less efficient than violent cut of the See (südliche Ukraine) Herring Gull. Im April 1984 und 1985 sowie im Mai 1986 Abb. 2: Das »clipping« (Zerschneiden) der Fischmöwe ist weniger effektiv als der starke führten die Autoren verhaltensbiologische Hieb der Silbermöwe. Studien an der Fischmöwe und der Silber­ möwe durch, die am Sivash See (südliche pushing with the breast. The greater body has a primitive vocal repertoir, producing Ukraine) Mischkolonien bilden. mass of Great Black-headed Gull gave it only eight different types of calls. Like Es wird die Besetzung des Brutplatzes, an advantage over the Herring Gull. La. L. melanocephalus, L. relictus and L ge­ der Nestbau, die Eiablage und das Brut­ cachinnans were more successful in ne/, L. ichthyaetus has no special vocal­ geschäft bei beiden Arten beschrieben oophagia, when 2 or 3 individuals cooper­ izations expressing warning, anxiety, und die gegenseitige Beeinflussung auf ated (Fig. 1). In this case, one bird at­ alarm or aggressiveness. This acoustic den zeitlichen Ablauf der einzelnen Pha­ tacked a victim and enticed it from the evidence supports the theory thatL. ich­ sen dargestellt und diskutiert. Auch wird nest; meanwhile the predator behind thyaetus is closely related to »primitive« das zwischenartliche Predationsverhal- snatched an egg (or a chick) from the nest, gulls or to species that have formed even ten (Eier- und Jungenraub) beschrieben. pecked it through and ate.The owner of earlier (B uzun & M ierauskas 1987; Mie­ the nest didn’t persuit the robber eating rauskas 1987; Mierauskas & B uzun References it’s egg but returned to the nest. We 1988). haven’t observed a case when a predator, Burger, J. (1979): Competition and predation: From the viewpoint of defence behaviour, Herring Gulls versus Laughing Gulls. - eating the stolen egg, would attack the L. ichthyaetus has a low defence capacity. nest again. Condor 81: 269-277. It usually defends only the nest, but not the Buzun, V. & P. Mierauskas (1987): Behaviour of L. a. cachinnans often attacked nests of colony, beating the intruder with wings, by the Mediterranean Gull (Larus their conspecifics. Usually La. cachin­ jabbing posture or passively sitting in melanocephalus) during colony formation nans that had lost their nests became pre­ dense colonies(Z ubakin 1976). Contrary and the early breading stages. - Bull. Mos- dators. In the colony there were always a to L. ichthyaetus, the Herring and Com­ kowskovo Obscestva Ispytatelei Prirody - group of birds constantly engaged in pre­ mon Gulls as well as other »progressive« ser. Biologia 92,3: 27-36. (Russian). Buzun, V. & P. Mierauskas (1988): Develop­ dation. Others did that rather seldom.