Study

Supplementary feeding increases reproductive success in carrion crows Corvus corone in farmland in Scotland

  • Published source details Yom-Tov Y. (1974) The Effect of Food and Predation on Breeding Density and Success, Clutch Size and Laying Date of the Crow (Corvus corone L.). Journal of Animal Ecology, 43, 479-498

Actions

This study is summarised as evidence for the following.

Action Category

Provide supplementary food for birds or mammals

Action Link
Farmland Conservation

Provide supplementary food for songbirds to increase reproductive success

Action Link
Bird Conservation

Provide artificial nesting sites for songbirds

Action Link
Bird Conservation

Provide nest boxes for birds

Action Link
Farmland Conservation
  1. Provide supplementary food for birds or mammals

    A replicated and controlled study in mixed farmland in north-east Scotland between 1971 and 1973 (Yom-Tov 1974) found that carrion crow Corvus corone nestlings in nests provided with supplementary food had significantly higher hatching, survival and fledging rates than those in control (unfed) nests. With human ‘predation’ included: 79% of fed nests hatching at least one chick (n = 11), 71% having at least one chick surviving for ten days and 71% fledging at least one chick (n = 10) compared to 61% (n = 28), 54% (n = 15) and 43% (n = 12) for controls. With human ‘predation’ excluded: 92% of fed nests hatching at least one chick (n = 12), 83% having at least one chick surviving for ten days and 83% fledging at least one chick (n = 10) compared to 55% (n = 22), 55% (n = 12) and 45% (n = 10) for controls. Nestlings from fed nests, however, were no heavier than those from controls, when comparing first-hatched with first-hatched etc. Supplementary food consisted of one domestic hen’s egg and five dead hen chicks provided every day from when laying began and increasing to one egg and ten chicks from the seventh day after hatching until fledging. Other experiments in this study found that winter feeding (a hen’s egg and five chicks provided between January and April 1973) led to crows laying clutches earlier but did not affect clutch size (average laying date of April 13th and 4.4 eggs/clutch for fed territories, n = 10 vs April 18th and 4.3 eggs/clutch for controls, n = 21). Further experiments examined the effect of moving supplementary food further from nests, but the author argues that these results are confounded by supplementary food being taken by non-target birds. Finally, additional experiments in the study found that crow nesting density did not increase following the provision of supplementary food and additional nesting sites in breeding territories.

     

  2. Provide supplementary food for songbirds to increase reproductive success

    A replicated and controlled study in mixed farmland in north-east Scotland between 1971 and 1973 (Yom-Tov 1974) found that carrion crow Corvus corone nestlings in nests provided with supplementary food had significantly higher hatching, survival and fledging rates than those in control (unfed) nests (with human ‘predation’ included: 79% of 11 fed nests hatching at least one chick, 71% of ten having at least one chick surviving for ten days and 71% fledging at least one chick vs. 61% of 28, 54% of 15 and 43% of 12 for controls). Nestlings from fed nests, however, were no heavier than those from controls, when comparing first-hatched with first-hatched etc. Supplementary food consisted of one domestic hen’s egg and five dead hen chicks provided every day from when laying began and increasing to one egg and ten chicks from the seventh day after hatching until fledging. Other experiments in this study found that winter feeding (a hen’s egg and five chicks provided between January and April 1973) led to crows laying clutches earlier but did not affect clutch size (average laying date of April 13th and 4.4 eggs/clutch for ten fed territories vs. April 18th and 4.3 eggs/clutch for 21 controls). Further experiments examined the effect of moving supplementary food further from nests, but the author argues that these results are confounded by supplementary food being taken by non-target birds. Finally, additional experiments in the study found that crow nesting density did not increase following the provision of supplementary food and additional nesting sites in breeding territories, discussed in ‘Provide artificial nesting sites’.

     

  3. Provide artificial nesting sites for songbirds

    A controlled study in mixed farmland in north-east Scotland in 1971 (Yom-Tov 1974) found that carrion crows Corvus corone did not nest in artificial trees, irrespective of whether they were provided with supplementary food or not. In one experiment, a line of 15 artificial trees (3-6 m branches tied to fence posts and provided with an old crow’s nest) were set up, approximately 70 m apart. Two pairs of crows established territories, but neither attempted to breed. A second experiment provided a single artificial tree in two occupied territories, 70 m from the tree used by the resident pair. Neither artificial tree was used, as the resident pairs successfully defended their territories. This study also investigated the effects of supplementary feeding on crow reproduction, discussed in ‘Provide supplementary food to increase reproductive success’.

     

  4. Provide nest boxes for birds

    A controlled study in mixed farmland in northeast Scotland in 1971 (Yom-Tov 1974) found that carrion crows Corvus corone did not nest in artificial trees, irrespective of whether they were provided with supplementary food or not. In one experiment, a line of 15 artificial trees (3-6 m branches tied to fence posts and provided with an old crow’s nest) were set up, approximately 70 m apart. Two pairs of crows established territories, but neither attempted to breed. A second experiment provided a single artificial tree in two occupied territories, 70 m from the tree used by the resident pair. Neither artificial tree was used, as the resident pairs successfully defended their territories.

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