Second-breeding events of the common kestrel (Falco tinnunculus) in the Czech Republic

The laying of two clutches in a single breeding season can increase the fitness of the parent birds and stabilise a population. Our study analysed the rate of second-breeding attempts in the common kestrel (Falco tinnunculus) population in the Czech Republic. In the research, a total of 8,049 common kestrel nests were checked between 1979 and 2019. Of the 1,197 breeding events recorded during the study period in Moravia, 1,184 cases were first clutches and 13 cases (1.1%) were second breeding attempts. In Bohemia, a total of 6,852 breeding events were observed during the same study period, of which 6,811 were first clutches, 32 cases were late breeding attempts and 9 cases (0.1%) were second clutches. Second breeding events occurred only rarely, mainly during population outbreaks of prey species. During the mass outbreak of the common vole (Microtus arvalis) population in the Czech Republic in 2019, 5 (5.2%) of the 97 studied common kestrel pairs nested for the second time in Moravia; in Bohemia, second clutches were recorded in 3 (8.1%) of the 37 studied pairs. The second breeding attempts were recorded at an altitude of 272 ± 123 m (mean ± SD, range 179–560 m, n = 22) and commenced between 24 June and 25 July (29 June on average, n = 5). The range of the time gap between the first and the second clutch was 54 to 92 days (70.8 ± 16.3 days, n = 5). The second clutches consisted of an average of 4.1 ± 0.9 eggs (range 3–6, n = 12), with an average of 3.7 ± 0.9 fledglings in each successful breeding pair (range 2–5, n = 11) and 2.6 ± 1.9 fledglings for each initiated breeding attempt (range 0–5, n = 16).