Birders, I thought this would be of interest. Regi ____________ “The future of the world is nuts.” Philip Rutter, founder of the American Chestnut Foundation
Begin forwarded message: > From: The Cottonwood Post <comment-re...@wordpress.com> > Date: January 8, 2021 at 11:12:29 AM EST > To: rltcay...@gmail.com > Subject: [New post] Mojave Desert bird populations plummet due to climate > change > Reply-To: The Cottonwood Post > <comment+e3mod154-af_gevuwrh0...@comment.wordpress.com> > > > Respond to this post by replying above this line > New post on The Cottonwood Post > > > Mojave Desert bird populations plummet due to climate change > by Stephen Carr Hampton > Two recent papers concluded that many breeding bird species in southern > California and Nevada deserts have declined dramatically due to climate > change. > > In their abstract, Iknayan and Beissinger (2018) summarized, "We evaluated > how desert birds have responded to climate and habitat change by resurveying > historic sites throughout the Mojave Desert that were originally surveyed for > avian diversity during the early 20th century by Joseph Grinnell and > colleagues. We found strong evidence of an avian community in collapse." > > > They re-surveyed 61 sites originally surveyed by Grinnell teams in the early > 20th century (primarily between 1917 and 1947). > Of 135 species assessed (which included some wintering and migrating species, > as well as breeding species), 39 had significantly declined; only one (Common > Raven) had increased. This was in stark contrast to similar assessments they > conducted of Sierra and Central Valley sites, where more species had > increased than decreased and there were no overall declines (not to say there > weren't winners, losers, and range shifts within those regions). > > > Figure 1B from Iknayan and Beissinger (2018). Every study site had fewer > species than previously-- on average each site had lost 43% of their species. > Detailed analyses suggested less rainfall and less access to water was the > primary driver. Habitat change only affected 15% of the study sites and was > of secondary importance. They found no evidence of expansion of species from > the hotter, drier Sonoran Desert (e.g. Phainopepla, Verdin, Black-throated > Sparrow) into the Mojave Desert. > > Consistent with a community collapse, declines were greatest among species at > the top of food chain -- carnivores such as Prairie Falcon, American Kestrel, > and Turkey Vulture. Insectivores were the next most impacted, and herbivores > the least. But the declines affected both common and rare species, both > generalists and specialists. > > > Figure 1B from Iknayan and Beissinger (2018), which I've augmented with > species labels from the database available in the supplementary materials. > Other significant losers (red dots), in order of degree of decline, included > Western Kingbird, Western Meadowlark, Black-chinned Sparrow, Lawrence's > Goldfinch, Bushtit, Ladder-backed Woodpecker, and Canyon Wren. The yellow > dots are newly invasive species: Chukar, Eurasian Collared-Dove, Eurasian > Starling, and Great-tailed Grackle. > A follow-up study by Riddell et al (2020), also involving Iknayan and > Beissinger, focused on the thermoregulatory costs -- the water requirements > to keep cool -- for the declining species. They found that "species’ declines > were positively associated with climate-driven increases in water > requirements for evaporative cooling and exacerbated by large body size, > especially for species with animal-based diets." Larger species get much of > their water from the insects they eat. They estimated larger species would > have to double or triple their insect intake to meet their water needs, > though insect abundance is lowest July thru September. > > > American Kestrels were among the biggest losers in the study, struggling to > meet their cooling needs. > Intriguingly, they found that 22 species had actually declined in body size > over the last century, consistent with Bergmann's Rule, and had reduced their > cooling costs up to 14%. These species fared better. Current climate change, > however, is at least ten times more rapid than any previous warming event, > during which many species evolved. They estimated cooling costs have already > increased 19% and will reach 50% to 78% under most scenarios, far > outstripping any species' ability to evolve through the current rapid warming. > > These results stand in stark contrast to the Pacific Northwest, where many of > the same bird species (e.g. Anna's Hummingbird, Turkey Vulture, Northern > Mockingbird) are increasing. This is consistent with projections which > generally show individual declines along species' southern edge and > expansions at the north edge of their range (see Audubon climate projection > maps for individual species). > > Iknayan and Beissinger conclude, "Our results provide evidence that bird > communities in the Mojave Desert have collapsed to a new, lower baseline. > Declines could accelerate with future climate change, as this region is > predicted to become drier and hotter by the end of the century." > > Stephen Carr Hampton | January 8, 2021 at 8:12 am | Categories: Uncategorized > | URL: https://wp.me/paaz6L-ap > Comment See all comments > Unsubscribe to no longer receive posts from The Cottonwood Post. > Change your email settings at Manage Subscriptions. > > Trouble clicking? 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