Patterns and consequences of egg destruction among joint-nesting acorn woodpeckers

• Published in: Animal behaviour Vol. 50; no. 3; pp. 607 - 621
• Main Authors: Koenig, Walter D., Mumme, Ronald L., Stanback, Mark T., Pitelka, Frank A.
• Format: Journal Article
• Language: English
• Published: Kent Elsevier Ltd 1995; Elsevier; Harcourt Brace Jovanovich Ltd
• Subjects: Animal behavior; Animal ethology; Aves; Biological and medical sciences; Birds; Fundamental and applied biological sciences. Psychology; Melanerpes formicivorus; Psychology. Psychoanalysis. Psychiatry; Vertebrata; California; United States; North America; America; Nesting; Destruction; Egg; Sexual competition; Synchronization; Breeding behavior; Reproduction; Vertebrata; Cooperative breeding; Female; Intraspecific association; Aves; Egg laying behavior; Melanerpes formicivorus; Field study
• ISSN: 0003-3472; 1095-8282
• DOI: 10.1016/0003-3472(95)80123-5

Reproductive competition among joint-nesting female acorn woodpeckers, Melanerpes formicivorus, culminates in the removal and subsequent destruction of eggs laid by co-breeders. Females destroying eggs gain both by synchronizing egg laying and by having more of their own eggs incubated in the final clutch. Here results are summarized based on observations of 19 joint nests. Egg destruction accounted for the loss of 38% of all eggs laid. Either or both joint-nesting females destroyed eggs at the same nest, and a female that destroyed eggs during one nesting attempt sometimes had her own eggs destroyed during the next. Egg destruction was not moderated by the genetic relatedness of joint-nesting females and was apparently unrelated to behavioural dominance, but substantially lowered per female success of three- compared with two-female nests. Females did not discriminate between eggs; thus egg destruction ended when both females laid normal eggs simultaneously in the nest cavity. However, egg destruction ended most frequently when a female did not destroy an egg laid by her co-breeder 1 day prior to laying her own first egg. Such failures to destroy eggs entail short-term fitness costs that may be compensated by the potential for reciprocity across breeding attempts. Abnormally small ‘runt’ eggs, rarely found in other species of birds, were commonly laid as the first egg of the clutches of one or both joint-nesting females. The laying of runt eggs may allow females to destroy normal eggs laid simultaneously by their co-breeders. Egg destruction is a major constraint on the degree to which females nest jointly. More generally, egg destruction and its associated behaviour patterns demonstrate that reproductive interference can be as complex and destructive within groups of close relatives as between unrelated individuals.