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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Mid-summer arrival by Blue Grosbeaks at the northern extent of their breeding range: evidence for dual breeding? (2021)
Titre original:	Mid-summer arrival by Blue Grosbeaks at the northern extent of their breeding range
Auteurs :	David L. Swanson, Auteur ; Reza Goljani Amirkhiz, Auteur
Type de document :	Article
Dans :	Journal of Field Ornithology (92(2) June, 2021)
Article en page(s) :	127-142
Langues:	Anglais
Mots-clés:	Passerina caerulea ; South Dakota ; arrival phenology ; citizen science ; northern range boundary ; temporal occurrence
Résumé :	Anecdotal observations of mid-summer arrival of Blue Grosbeaks (Passerina caerulea) in South Dakota, in the northern portion of their breeding range, suggest that this species may show a pattern of arrival at the northern breeding grounds that differs from that of other species of migrant birds. We assessed this possibility using three different approaches: (1) data mining from a citizen-science database for South Dakota bird observations, (2) citizen-science roadside surveys in South Dakota in 2019 and 2020, and (3) analyses of temporal occurrence patterns from eBird data for the southern and northern portions of the breeding range. Observations of Blue Grosbeaks from eastern and central, but not western, South Dakota peaked from late June through early August, a pattern of later arrival than other species of migrant birds occupying similar habitats. Results of citizen-science roadside surveys revealed that 57 (2020) to 76% (2019) of the breeding population of Blue Grosbeaks in eastern and central South Dakota arrived after mid-June. Finally, eBird data revealed that Blue Grosbeak occurrence decreased from May to mid-June through August in the southern portion of their breeding range (Texas and Oklahoma), but increased from mid-June through early August in the northern portion of their range in South Dakota. Mid-summer arrival phenology in South Dakota and different temporal occurrence patterns in the northern and southern portions of their breeding range are consistent with a hypothesis of dual breeding for a portion of the Blue Grosbeak population in central North America, with a first brood in the southern and a second in the northern part of their breeding range. However, other possible explanations for these temporal differences in occurrence patterns, such as wandering birds that failed to acquire breeding territories in the southern portion of the range, have not yet been conclusively ruled out. If a dual breeding strategy is confirmed, this would represent the first documentation of a south-then-north pattern for dual breeding in the New World.
En ligne :	https://onlinelibrary.wiley.com/doi/abs/10.1111/jofo.12367

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