For the past several years I've focused my spring season reports in North American Birds on the curious spike in our Region of records of vagrants and half-hardies during March. This generally under-appreciated pattern is not only very well-documented but also, I argue, potentially a very significant indicator of how birds are responding to our changing environment.
The idea is that as temperatures increase and day length increases rapidly during March, birds that have over-wintered in favorable micro-environments (often involving feeders) begin to move around. Many of these birds were undetected or at least unreported through the winter, but their March movements increase the likelihood that they will cross paths with birders. The basic pattern is very recognizable regardless of whether a particular winter survivor belongs to an extralimital species (like Rufous Hummingbird, Varied Thrush, Painted Bunting, or Black-headed Grosbeak) or a regularly occurring breeder/migrant that normally winters far to the south (like Orange-crowned Warbler, Northern Parula, or Rose-breasted Grosbeak): if people were aware of the bird through the winter, it abruptly disappears during March; at the same time, previously undetected birds begin to be reported as they roam around. The parallel between vagrant species and half-hardies implies that the two groups might be doing something similar--and that the "vagrants" might be doing more than being lost. Anyway, regarding the following chestnut, I'd say that the accumulation of data strongly supports the over-wintering hypothesis. From: Shaibal Mitra [[email protected]] Sent: Wednesday, March 26, 2008 12:37 PM To: [email protected] Subject: Rose-breasted Grosbeak, Bay Shore, Suffolk County Pat Lindsay just called with news of a young male Rose-breasted Grosbeak singing at Gardiner County Park, which is essentially due north across Great South Bay from Fire Island Lighthouse. Her description rules out Black-headed Grosbeak, but the question of whether this bird wintered locally or just arrived from afar can probably only be settled if other Neotropical Cardinalids, tanagers, etc. show up coastally today or tomorrow. Shai Mitra Bay Shore, NY ________________________________ Connect with CSI on Social Media><http://csitoday.com/social_media/> -- NYSbirds-L List Info: http://www.NortheastBirding.com/NYSbirdsWELCOME http://www.NortheastBirding.com/NYSbirdsRULES http://www.NortheastBirding.com/NYSbirdsSubscribeConfigurationLeave.htm ARCHIVES: 1) http://www.mail-archive.com/[email protected]/maillist.html 2) http://www.surfbirds.com/birdingmail/Group/NYSBirds-L 3) http://birdingonthe.net/mailinglists/NYSB.html Please submit your observations to eBird: http://ebird.org/content/ebird/ --
