Nest Defence and Parental Investment in the Redwing Turdus iliacus

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Abstract
The nest defense behavior of the redwing T. iliacus was examined to determine whether changes occur during the breeding season, whether defense intensity is related to reproductive success, and to study fluctuations in the probability of predation. Alarm calling rate was used as a measure of nest defense intensity. The rate of alarm calling increased throughout the breeding cycle. No significant differences were found in total alarm calling rate between early and late breeders, or between groups with different clutch or brood sizes. The probability of predation increased as the breeding season proceeded. The results are discussed in relation to predictions derived from 3 hypotheses of parental investment (cumulative investment, expected benefit, and increasing predation).