North American Birds

VOLUME 70 NO1 2017

A Quarterly Journal of Ornithological Record Published by the American Birding Association. The mission of the journal is to provide a complete overview of the changing panorama of our continent’s birdlife.

Issue link: http://nab.aba.org/i/936087

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N O R T H A M E R I C A N B I R D S 10 A M E T H Y S T - T H R O AT E D H U M M I N G B I R D I N Q U É B E C There is a previous record of Amethyst- throated Hummingbird in San Benito, Texas, July 4, 2006, but it was not accepted by the Texas Birds Record Committee. Neverthe- less, the species is obviously much more ex- pected to show up in southern Texas than in Québec or anywhere in Canada. Amazingly, at the time of writing, another Amethyst- throated Hummingbird was documented on the West Texas Hummingbird Cam in the Davis Mountains, October 14, 2016 (Bryan and Floyd 2017). Other Mexican hummingbirds are not un- known at far-flung locations in the U.S and Canada, especially in the summer months, when there is no lack of flowers or feeders from Mexico all the way to Canada: White- eared Hummingbird in Florida (August 2004) and Michigan (August 2005), Mag- nificent Hummingbird in Arkansas (July 1993), Violet-crowned Hummingbird in Virginia (July 2009), and Broad-billed Hum- mingbird in Michigan and New York (both in June 1996). This out-of-the-blue record may also recall the infamous Xantus's Hum- mingbird that caught British Columbia bird - ers off guard in 1997–1998. In practically any instance of a seemingly outlandish extralimital record, the possibility of a captive origin or assisted transport must be considered. A request was accordingly made to the International Species Informa - tion System (I.S.I.S), a global database of zoo in highlands, where all Amethyst-throated Hummingbirds are thought to be found. Al- titudinal migration is believed to play a role in the seasonal distribution of tropical birds over an elevational gradient (Stiles 1989, Powell and Bjork 1995, Winker et al. 1997), but remains a little studied and poorly un- derstood phenomenon (Fraser et al. 2008). As seasonal shifts in abundance due to al- titudinal migration are difficult to separate from lateral, seasonal habitat shifts at the same elevation, recent studies with stable- hydrogen isotope analysis on feathers have proven altitudinal migration to be common in several montane hummingbird species (Fraser et al. 2008). Although the Amethyst- throated Hummingbird situation has not been properly studied yet, there is at least anecdotal evidence that the species exhibits seasonal shifts in abundance at various sites in the range of the nominate subspecies (M. Retter, personal communication). The occurrence of Amethyst-throated Hummingbird north of Mexico was earlier predicted by Williamson (2001). Accord - ing to the author of this prediction (S. Wil - liamson, personal communication), it makes about as much sense as Mexican Violetear (Colibri thalassinus), another inhabitant of the highlands of the Sierra Madre Oriental and regular vagrant in the ABA area, notably to Québec (2008), Alberta (1993), and Brit- ish Columbia (2014). only slightly abraded overall. It is possible this bird may be over a full year old, given that the bird had a complete gorget and birds in this genus are slow to develop that aspect of the plumage (S. Williamson, personal communication). A lack of basic knowledge on breeding seasonality in the Amethyst- throated Hummingbird is a major hurdle to the correct assessment of age. Extralimital sightings of Amethyst- throated Hummingbird appear to be quite rare. In February 2012, an individual was seen by several birders in Parque Nacional Cumbres de Monterrey in the state of Nue- vo Leon, Mexico (eBird 2016). In general, hummingbirds can find abundant nectar food resources only during a limited period in a given habitat; when resources begin to become scarce, they need to move to other areas (Lara 2006). Peak flowering periods fluctuate and are unpredictable, especially Fig. 6. Despite its large size, this Amethyst-throated Hummingbird was significantly shier than the Ruby-throated Hummingbirds it was feeding with. Even when visiting frequently, the vagrant kept its visits brief and quickly retired to nearby trees after feeding. Photo by © Annie Lavoie. Fig. 5. The all important tail-shot. Perhaps the most impor- tant field mark in separating this species from the similar Blue-throated Hummingbird is the tail pattern. Amethyst- throated shows broad, but indistinct gray corners on the outer tail feathers. On Blue-throated, these tail markings are clean white. This feature is readily apparent from a variety of angles and even when other aspects of plumage are incon- spicuous due to light conditions. Photo by © Annie Lavoie.

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