FOOD AS A MECHANISM OF DENSITY‐DEPENDENT REGULATION OF BREEDING NUMBERS IN THE MERLIN, FALCO COLUMBARIUS

E-ISSN： 1939-9170|82|3|860-867

ISSN： 0012-9658

Source： Ecology, Vol.82, Iss.3, 2001-03, pp. : 860-867

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Abstract

Population regulation of Merlins (Falco columbarius) was studied during 16 years in a small area supporting up to 11 breeding pairs, and during seven years in an expanded area where breeding numbers varied between 28 and 38 pairs. During the study period, the previously regular 4‐yr cyclicity in rodent abundance disappeared, for unknown reasons. The functional form of density dependence agreed with a version of the Ricker equation, which showed that there was direct density dependence in the number of Merlin pairs attempting to breed. Moreover, in seasons with high small‐rodent density, local population density of Merlins increased, and breeding territories were established in areas that, in other years, did not sustain breeders. Overwinter loss of males was directly related to breeding population size in the preceding year, as well as to small‐rodent density. In contrast, overwinter loss of females appeared to be independent of breeding population size and food abundance in the preceding year.