Robbing Behavior of Roseate Terns
1973; Oxford University Press; Volume: 90; Issue: 3 Linguagem: Inglês
10.2307/4084163
ISSN1938-4254
Autores Tópico(s)Insect and Arachnid Ecology and Behavior
ResumoTHE increasing number of reports in recent years show the habit of stealing food from other birds (cleptoparasitism) to be a fairly widespread phenomenon among the Laridae (Rand 1954, N•rrevang 1960, Hatch 1970, Hays 1970, Hopkins and Wiley 1972).Where Laridae or Stercorariidae are the antagonists, they often band together into chasing groups of varying size (Belopol'skii 1957, Meinertzhagen 1959, Grant 1971) and the interactions can be complex (Hatch 1970).On Coquet Island (55 ø 20' N, 1 ø 32' W) and the nearby Farne Islands off the northeast coast of England, Roseate Terns, Sterna dougallii, rob other terns of their fish (Watt 1951, Bannerman 1962, Langham 1968).These parasitic terns operate singly, rather like foraging raptors, and the robbing behavior is therefore particularly suitable for studying the relationships between the parasites and their hosts.This paper describes the behavior on Coquet Island and considers various responses by the Roseate Terns to changes in the abundance and nature of the food supply brought to the island by the host population of terns.Coquet Island is flat and low, rising only about 10 m above sea level.It has an area of almost 70,000 square meters, most of which is covered by low-lying vegetation.Between May and August each year, some 50,000 square meters are occupied by breeding terns of various species.In 1969 when the major part of this work was undertaken, the island supported about 250 pairs of Roseate Terns, 1,300 pairs of Common Terns, S. hirundo, 700 pairs of Arctic Terns, S. paradisaea, 200 pairs of Sandwich Terns, S. sandvicensis, and, in addition, 105 pairs of Black-headed Gulls, Larus ridibundus.iV•ETI-I O D S Between iVfay and July 1968 the airspace above the island was monitored periodically to determine which tern species were being robbed and in what manner.In July 1969 a hide was situated facing area A (Figure 1), which was colonized mainly by Common Terns.Daily observations of robbing behavior were subdivided into 15-minute watches for a total of almost 61 hours (243 watches) on 10 days between 23 July and 7 August 1969.During each watch the total number of Roseate Terns actively parasitizing above area A was counted.Roseate Terns did not pursue other terns with fish but attacked them mainly by making brief, rapid swoops; all such flight maneuvers directed at terns carrying fish were scored as attacks, irrespective of whether or not the birds made physical contact.Successful attacks were those in which the parasite gained possession of another tern's fish.All four tern species carry fish crosswise in the bill.iVfost birds (98 percent) carried only one fish but a few (2 percent) carried more than one and sometimes as many
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