Common Tern Sterna hirundo and Arctic Tern S. paradisaea hybridization produces fertile offspring
* Correspondence author: firstname.lastname@example.org
1 Massachusetts Division of Fisheries & Wildlife, 1 Rabbit Hill Road, Westborough, Massachusetts 01581, USA;
2 Central Connecticut State University, 1615 Stanley Street, New Britain, Connecticut 06053, USA;
3 Eastern Connecticut State University, 83 Windham Street, Willimantic, Connecticut 06226, USA.
Common Terns Sterna hirundo and Arctic Terns S. paradisaea have broad breeding distributions in North America and Eurasia, but their area of overlap is not extensive, as the Common Tern breeding range is largely south of that of the Arctic Tern (Cramp 1985; Hatch 2002; Nisbet 2002a). On the northwest Atlantic coast of the USA, where our study occurred, the species’ breeding ranges overlap between 41°N and 52°N (Hatch 2002). Because morphological and molecular evidence suggests that Arctic and Common Terns are very closely related (Bridge et al. 2005), it follows that hybridization could occur. Mixed Arctic/Common tern pairs, including multi-year pairings, have indeed been reported in the wild (Kullenberg 1946; Panov 1989; Debout & Debout 1989 in McCarthy 2006) as have presumed hybrid young (Degland & Gerbe 1867, Suchetet 1896). Molecular confirmation is, however, absent.
In June 2007, CSM first observed a Common Tern and an Arctic Tern attending two chicks on Penikese Island (41°27’N, 70°55’W) in Buzzards Bay, Massachusetts, USA. Observations over the next three weeks provided further support that these birds were a mated pair. We located this pair in most years from 2007 to 2014 and here we present behavioural and molecular evidence for a long-term pair bond and hybridization of these birds that resulted in production of fertile offspring. We report on: analysis of mitochondrial and nuclear DNA; characteristics of nests, eggs, and young (F1 hybrids); and reproductive performance of the mixed pair in comparison to the parent species. We describe an adult F1 hybrid and its offspring (B1 hybrids) that resulted from backcrossing to a Common Tern and discuss factors that may have contributed to the interspecific pairing at this site.
We dedicate this paper to Jeremy J. Hatch, who had an affinity for Arctic Terns. We thank the New Bedford Harbor Trustee Council, the MassWildlife-Natural Heritage & Endangered Species Program, Eastern Connecticut State University, CSU-AAUP Faculty Research Grant, and the Island Foundation for support; the Penikese Island School for transportation; the Woods Hole Oceanographic Institution for logistical support; J. Gahagan for photographing the hybrid adult; H. Goyert for bringing the grey tern chick on Bird I. to our attention; M. Bromberg and G. Vecchio for translations of papers; and D. Hayward, I. C. T. Nisbet, L. Welch, S. Williams, and the Gulf of Maine Seabird Working Group for information. M. Collinson and an anonymous reviewer improved the manuscript. We especially thank many seasonal biologists and volunteers, including: W. Houghton, K. Blake, L. Mostello-Wetherbee, J. Ebel, L. Flieger, C. Challion, J. Cunningham, W. van Dijk, A. Eibin, T. Maikath, N. French, E. Lencer, K. Scantlebury, S. Woodward, J. Hatt, S. Schulwitz, A. Crabbe, M. Servison, K. Justham, R. Herman, K. DeMoranville, J. Correia, P. Cunningham, E. LaPlante, A. Anderssen, D. Dombkowski, A. Smith, E. Berge, and C. Bates.
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