Predation on Eggs and Nestlings of Common Murres (Uria aalge) at Bluff, Alaska

We studied predation on the eggs and nestlings of Common Murres at Bluff, Alaska, in 1987, 1988, and 1991. Common Ravens and Glaucous Gulls were the primary predators of eggs. Nestling losses were low, and few could be attributed to predation. A raven usually took a murre egg after pulling the incub...

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Bibliographic Details
Published in:Colonial waterbirds 1996-01, Vol.19 (2), p.186-198
Main Authors: James H. S. Schauer, Murphy, Edward C.
Format: Article
Language:English
Subjects:
Breeding
Breeding seasons
Cliffs
Eggs
Foraging
Foxes
Hunting
Larus hyperboreus
Marine
Predation
Predators
Ravens
Uria aalge
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Summary:We studied predation on the eggs and nestlings of Common Murres at Bluff, Alaska, in 1987, 1988, and 1991. Common Ravens and Glaucous Gulls were the primary predators of eggs. Nestling losses were low, and few could be attributed to predation. A raven usually took a murre egg after pulling the incubating adult from the egg and off the cliff; we never observed ravens taking abandoned eggs. The intensity of raven predation was highest on earliest-laid eggs. Virtually all raven attacks were on murres that had no active breeding neighbors at the time of the attack. Non-incubating adult murres typically flushed as a raven approached, leaving sites where a raven could then land and attack an incubating adult. Raven predation accounted for up to about half of egg losses on study plots. Raven predation acts evolutionarily as directional selection against early, asynchronous egg-laying. However, the intensity of this selection is reduced by high probability of relaying for eggs lost earliest in the season and the lack of a marked seasonal decline in breeding success of murres at this colony. Except for a few rare occurrences, Glaucous Gulls took only unattended or abandoned eggs, often following human disturbances or rock slides. Gulls preyed predominately on eggs and only rarely on nestlings. Most gull predation on eggs occurred early in the breeding season of murres, when human disturbance was highest and murres seemed most likely to temporarily abandon eggs. Gull predation and accidental dislodgment of eggs by flushing adults likely accounted for locally high losses of eggs on days when human hunters discharged firearms and shot adults on or near the cliffs.
ISSN:0738-6028
DOI:10.2307/1521855