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Providing evidence to improve practice

Individual study: Encouraging double clutching slightly reduces productivity in bald eagles Haliaeetus leucocephalus in marshland sites in Florida, USA

Published source details

Wood P.B. & Collopy M.W. (1993) Effects of Egg Removal on Bald Eagle Productivity in Northern Florida. The Journal of Wildlife Management, 57, 1-9

This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Remove eggs from wild nests to increase reproductive output Bird Conservation

A replicated, controlled study in two marshland sites in Florida, USA, between 1985 and 1990 (Wood & Collopy 1993) found that 78% of 58 bald eagle Haliaeetus leucocephalus pairs that had their first clutch removed for hand-rearing (‘donor nests’) between 1985 and 1988 laid replacement clutches within two months. Replacement clutches were slightly smaller than first clutches (58 first clutches averaged 2.1 eggs/clutch vs. 1.8 eggs/clutch for 45 second clutches). In one study area, donor nests produced fewer fledglings than control pairs (1.0 fledgling/nest for 16 donor nests vs. 1.5 fledglings/nest for 39 controls), but this was not true in a second area (1.2 fledgling/nest for 26 donor nests vs. 1.1 fledglings/nest for 41 controls). Donor nests were more productive in the year before eggs were removed than the year after donation (approximately 1.3 fledglings/clutch for 32 pairs the year before donation vs. 0.85 fledglings/clutch for 34 pairs the year after). A demographic model suggested that a donor population would be very slightly smaller than a control population after 25 years. Timing of clutch removal did not affect the speed or probability of replacement clutches being laid.