Thursday, March 8, 2012

How Climate Change might affect California Birds

As birders we are ingrained with an appreciation for the beauties of the natural world, and a fear of the impending loss of them.  Biodiversity is by no means taken for granted by birders (generally speaking of course).  This is why thousands of American birders congregate in southern Texas or Florida to see hundreds of species of birds in just a few days.  Anthropogenic climate change is a looming threat to avian diversity, and has been shown by many authors to pose risks as great as extinction for many of the world’s taxa.  Still, systems for ranking threats to species have often overlooked their vulnerability to climate change despite its widely appreciated consequences.  In an effort to quantify the vulnerability of California's birds to climate change, a recent publication by PRBO Conservation Science researchers here at the Palomarin field station (Tom Gardali, Nat Seavy, and Ryan DiGaudio) in collaboration with California Fish and Game develops a new method to evaluate the effects of climate change on birds, and pin-points species and subspecies of highest concern in California.
Coastal species such as these Wandering Tattlers or Common Murres (below) are quite vulnerable to climate change likely because rising ocean levels will alter rocky shorelines, beaches, or estuaries used by many species for foraging habitat (as with the tattlers) or nesting habitat (as with the murres).
According to the publication, California birds may be sensitive to climate change in any of the following ways: 1) habitat specialization—species with narrow habitat preferences may be more sensitive to climate change than habitat generalists; 2) physiological tolerances—species with broader physiological tolerances may be less likely to be affected by climate change because they are more resilient to extreme temperatures; 3) Migratory status—migratory species may be more sensitive to climate change because the timing of their movements critically depend on climatic conditions for survival and successful reproduction; and 4) Dispersability—species with poor dispersal ability may be more sensitive to climate change because they lack the mechanisms to rapidly habitat track.

Further, climate change poses risks to species by exposing them to any of the following conditions: 1) Changes in habitat suitability—exposure to changes in habitat structure in any of a variety of ways may pose risk if habitat suitability decreases for a given species; 2) changes in food availability—exposure to changes in the availability or abundance of food sources undoubtedly affects survival and reproductive success; and 3) changes in extreme weather—extreme weather has been shown numerous times to lead to low fecundity or even nest failure in many species.

The authors scored species on all of these seven criteria and ranked vulnerability of the top 25% of scores from most vulnerable to least vulnerable to climate change.  In doing so, they added five taxa not originally listed in the California Bird Species of Special Concern monograph (BSCC; 2008), and raised the priority of ten more.  Further, it was found that 21 of California’s 29 state or federally threatened or endangered species were susceptible to the consequences of climate change.

Some results:

Studies such as this provide a salient understanding of how anthropogenic climate change will affect natural populations, and are critical to effective conservation since threats such as climate change pose risk for extinction.  For instance, alpine species with restricted temperature tolerances would be unlikely to survive long-term global warming because habitat tracking ends at the top of the mountain.  Delimiting which taxa are most vulnerable will allow conservationists and managers to prioritize species of high concern and further work to protect them in addition to their habitat requirements.  

By Luke Musher

To read the open access article visit:

Gardali T, Seavy NE, DiGaudio RT, Comrack LA (2012) A Climate Change Vulnerability Assessment of California's At-Risk Birds. PLoS ONE 7(3): e29507. doi:10.1371/journal.pone.0029507

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