Breeding biology of the Common Kestrel in southern Africa (32°s) compared to studies in Europe (53°N)

Abstract

Van Zyl, A.J. 1999. Breeding biology of the Common Kestrel in southern Africa (32°s) compared to studies in Europe (53'N). Ostrich 70(2): 127- 132.

The breeding biology of 24 pairs of Southern African Kestrels Falco tinnunculus rupicolus was studied over two seasons in the Tarkastad District (32°S), South Africa, and compared to studies of the western European Kestrel Falco tinnunculus tinnunculus (53°N). Most Southern African Kestrels bred in old stick nests and on cliffs at densities comparable with average densities of European Kestrels (24.3 pairs. 100 km⁻² vs. 12–32 pairs. 100 km⁻²). Mean clutch size was smaller than found in Europe (3.21 eggs vs. 4.4 eggs) while incubation period at one nest was 26 days and within the range of the European Kestrel (26–31 days). Nestling (30–31 days) and post-fledging periods (32–39 days) were also similar to the range recorded for the European Kestrel (27–35 days and 13–31 days respectively). The number of chicks fledged was inversely related to laying date, as in Europe. Provisioning rates to nestlings were higher than in Europe (57.4 items.nest⁻¹ vs. 13–19.2 items.nest⁻¹), but the estimated size and amount of food delivered to the nest per day was lower (151.8 g.nest⁻¹ vs. 325 g.nest⁻¹). Chick growth rates were within the range measured for European Kestrel chicks (Ricklef's growth rate constant K = 0.257 vs. K = 0. 166 − 0.312) but wing feather-growth rate was marginally lower. Only clutch size fitted predictions of life-history theory over latitudinal gradients although more data is needed on other life-history parameters. I suggest that environmental variation resulting in differences in food availability and food quality are responsible for latitudinal trends in life-history traits.