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Sagebrush and Bell’s Sparrows

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Birders of the arid Southwest have been experiencing headaches this winter, and it is not just dehydration. The recent AOU split (here) of Sage Sparrow into two distinct species, Bell’s Sparrow (Artemisiospiza belli) and Sagebrush Sparrow (A. nevadensis), has led to an outbreak of head-shaking and hand-wringing on blogs, listservs, identification discussion groups, and even reviewer discussion groups in the region. Chris McCreedy of Point Blue Conservation Science provides us with an overview of the challenges and the field work being done to supply some answers.

The reason? It is quite difficult to tell the two species apart in the field (read here for an excellent summary by Peter Pyle of some apparent differences in plumage). Many contend that it is currently impossible to separate the two taxa in the field for a majority of individuals – and perhaps all of them. Despair deepens due to the inclusion of the ‘Mojave’ subspecies of Sage Sparrow (A. b. canescens) within Bell’s Sparrow and not with Sagebrush. ‘Mojave’ canescens are intermediate in appearance. Plus, the canescens wintering distribution appears to overlap heavily with Sagebrush in southeastern California, southern Arizona, and northwest Mexico.

From a broader perspective, each of these species winter in a part of the continent that is projected to be much hotter and drier in the future due to climate change. They winter in arid scrub habitats that respond dramatically to rainfall – and to lack thereof. Diminishing seed crops on their wintering grounds due to drought may decrease survival rates and individuals’ condition upon return to their breeding grounds.

Given that Sagebrush and Bell’s were once considered to be one species, differences between habitat preferences on their wintering grounds are not well-studied. Regional conservation plans that might consider conservation strategies for Sage Sparrows’ wintering habitat were likely written before the taxonomic split, and just as many listers found themselves with only an unsatisfying Sagebrush/Bell’s Sparrow on their lists after the split, the species themselves are left with a similarly unsatisfying, generic conservation strategy.

Given a lack of resolution in the species’ field identification, how can we survey birds to inform land managers and owners on how best to conserve these taxa? Point Blue Conservation Science (formerly PRBO) is currently in the field in southwestern Arizona, hoping to shed as much light as possible on these identification, distribution, and habitat questions. With support from Arizona Field Ornithologists and a cadre of amazing volunteers, we captured individuals at sites near Phoenix, Yuma, and Lake Havasu City during the first half of February 2014. We took measurements on as many of the previously-noted potential differences in field marks and morphology as we could find in the literature and online, have added a few of our own, assessed the appearance of some of these features in different lighting conditions, at different distances and with different optics, and explored apparent differences in habitat preferences between the two species. Dr. Adrienne Kovach (University of New Hampshire) has offered her assistance to help us ground our captures’ field identification with confirmation of individuals’ sex and species via DNA analysis.

Initial impressions suggest that Bell’s Sparrow winters farther east than was generally expected. In absence of detailed field study of multiple markings mentioned by Pyle above, we encourage observers to report their observations of wintering individuals as Bell’s/Sagebrush Sparrow (Sage Sparrow) from Pima, Pinal, and Maricopa Counties in Arizona, as well as in counties in western Arizona and southeastern California. Careful scope viewing is highly recommended, and one’s impressions of important field markings are definitely impacted by lighting conditions in the field. We have found that it may take me an hour to achieve good looks at only a small fraction of the many wintering Artemisiospiza one might find at a location. Further, we suggest observers photograph these whenever possible throughout the species’ ranges, and it is always useful to describe the vegetation where you find birds.

We hope to have analysis of this month’s work completed by the summer of 2014, and if additional proposals are successful, we are looking forward to adding more sites in Arizona and along an east-west transect across southern California during the winter of 2014-2015. If you are interested in volunteering in the field next season, we need you! Our volunteers enable us to increase capture rates and have made our project a success in Arizona. Please contact Chris McCreedy.