Individual study: Black-billed magpies Pica pica provided with a supplementary food source breed at higher densities and lay clutches earlier in Washington, USA
Knight R.L. (1988) Effects of Supplemental Food on the Breeding Biology of the Black-Billed Magpie. The Condor, 90, 956-958
This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.
Provide supplementary food for songbirds to increase reproductive success
A controlled before-and-after study in Washington, USA, in March-June 1979-82 (Knight 1988), found that twice as many black-billed magpies Pica pica nested, and that they began laying significantly earlier, in a 0.3 ha area of willow Salix spp. in 1981 when a dead bullock was cut open to locally increase invertebrate numbers, compared to 1979-80 and 1982 when there was no bullock present (eight nests in 1981, average laying date if 24th March vs. three or four nests and a laying date of 2nd-4th April in other years). There were no corresponding changes in two areas that were not supplied with a carcass (six and nine nests and 1st-6th April for all years studied). There were no differences in clutch size or the number of young fledged from nests with the carcass present. The bullock weighed approximately 450 kg and died between 1st and 7th March 1981 and attracted large numbers of blow flies (Calliphoridae), most of which had left by the 22nd March.