Costs and response to conspecific brood parasitism by colonial red-breasted mergansers
Costs of conspecific brood parasitism (CBP) are expected to be influenced by a species’ life history traits. Precocial birds lay large clutches, and clutches that have been enlarged by CBP can affect host fitness through a longer incubation period, displaced eggs, and lower hatching success. We examined costs and response to CBP by hosts in a population of colonial red-breasted mergansers (Mergus serrator; n = 400 nests over 8 years) within which 29% of parasitized clutches were enlarged considerably (≥ 15 eggs). Length of the incubation period did not increase with clutch size. The mean number of eggs displaced from a parasitized nest during incubation (2.8) was 2× greater than at an unparasitized nest (1.4). Hatching success declined by 2% for each additional egg in the nest. Thus, for a nest with ≥ 15 eggs, one or more fewer host eggs hatch relative to an unparasitized nest with the same number of host eggs, assuming equal probability of success for all eggs. Hosts were 40% more likely to desert nests receiving 2 or 6 experimental eggs relative to unparasitized control nests, although it is unknown whether hens deserting a nest renested elsewhere. Our study indicates that costs of CBP to hosts during nesting may be limited to those red-breasted mergansers incubating the largest clutches (≥ 15 eggs), and it raises questions about the adaptive significance of deserting a parasitized clutch.
KeywordsBreeding behavior Colonial nesting Conspecific brood parasitism Fitness costs Mergus serrator Red-breasted merganser
The authors are grateful for field assistance provided by A. Beaudet, D. Bilodeau, A. Comeau, A. Constantineau, M. Deveau, K. Francis, J. Haché, A. Hanks, P-É Hébert, N. Laplante, F. LeBlanc, S. Lefrançois, B. Martin, A. Rousseau, S. Seaborn, B. Spinney, E. Titman, R. Titman, S. Titman, and A. Wood. The late O. Fraser provided sea kayaks. M. Guigueno, F. Leighton, J. Eadie, and an anonymous reviewer provided valuable comments on earlier versions of the manuscript. Funding was provided by Bird Protection Quebec, Bishop’s University, Canadian Wildlife Federation, Delta Waterfowl Foundation, McGill University, Natural Sciences and Engineering Research Council of Canada (NSERC), New Brunswick Wildlife Trust Fund, North American Sea Duck Joint Venture, and Université Sainte-Anne. All grants were awarded to SRC and RDT except that from NSERC (awarded to NT). None of the funders had any influence on the content of the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. All procedures performed in studies involving animals were in accordance with the ethical standards of the institution at which the studies were conducted (permits # 1926 and #7329 at McGill University).
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