Individual study: Supplementary feeding increases breeding success, may increase breeding density and reduces predation in European jackdaws Corvus monedula in scrubland in southern Spain
Soler M. & Soler J.J. (1996) Effects of experimental food provisioning on reproduction in the jackdaw Corvus monedula, a semi-colonial species. Ibis, 138, 377-383
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Provide supplementary food for songbirds to increase reproductive success
A replicated and controlled before-and-after trial in scrubland, gullies and caves in southern Spain in 1980-3 (Soler & Soler 1996) found that European jackdaws Corvus monedula laid earlier, laid more eggs and had higher breeding success when given supplementary food, compared to either the same colonies in previous years, or to control colonies (average laying date of 25th April, 6.0 eggs/clutch and 48% of all eggs fledging for 13 fed nests vs. 27th April, 5.4 eggs/clutch and 20% of all eggs fledgingfor 18 experimental colonies in previous years vs. vs. 27th April, 5.4 eggs/clutch and 29% of all eggs fledging for 18 control colonies). Starvation rates were also lower in fed colonies (2.5 nestlings/nest starving in 12 fed nests vs. 3.4 nestlings/nest in 12 controls). Predation rates were lower in fed colonies (0% of 20 fed nests predated vs. 22% of 27 control nests) and the authors argue that this was due to better group defence in fed colonies due to higher breeding densities, although nesting densities were only significantly higher in one colony, comparing 1983 and 1982, other comparisons were non-significant (colony A when not fed: 56%, 63% and 56% of nests occupied in 1980-2 vs. 88% in 1983 when fed; colony B: when not fed: 50%, 67% and 33% of nests occupied in 1980-2 vs. 100% in 1983). Supplementary food consisted of four hens’ eggs for each jackdaw pair supplied twice a week and 4-7 kg of bread, continuously supplied.