In my previous two columns on the Breeding Bird Survey, I covered the background of this continental bird population monitoring program and looked at some of the species that have been increasing in Idaho since 1966. But the survey has been most important in identifying species populations that have been decreasing.
Bird conservation initiatives, such as Partners in Flight, which I coordinated from 2000 to 2014, depend on first identifying species that are going down. Second, we attempt to figure out why they are declining. And third, we take steps to eliminate or mitigate those factors through conservation actions.
With BBS data, the first step is by far the easiest. Bird conservation is enormously enriched today, with 55 years’ worth of data to examine. We now have the luxury of working on more advanced ways of analyzing those data rather than wondering where we can get data in the first place.
Partners in Flight also looks at data in addition to population trend — the size of the species’ population, the size of its breeding and nonbreeding ranges, and threats to the species around the year. But the BBS population trend is the backbone of the assessment. For now, we’ll look at species that are declining in Idaho and compare those trends to those at the scale of scale of North America.
Species with the steepest statistically significant declines in Idaho include ruddy duck (-7.2% per year), plumbeous vireo (-7.2%), redhead (-6.7%), snowy egret (-6%), California gull (-5.2%), and blue-winged teal (-5%). Five of these species are waterfowl and waterbirds. This is the sort of evidence that sends ornithologists looking for overall patterns of wetland conservation. Are we losing wetland acres? Are we losing water quality? Both?
The plumbeous vireo is found almost exclusively south of the Snake River Plain while Cassin’s vireo — a close relative — is the one we have from the Treasure Valley and north. These are species of dry ponderosa pine forests, hanging out with western tanagers and yellow-rumped warblers. Cassin’s vireo is significantly increasing, so this situation is a puzzle. Could it be related to forest fires? That’s something we can examine by looking at forest fire locations, sizes, severities, and other information south and north of the Snake River. But figuring out causes of trends is not at all easy.
Next are horned lark (-3.2%), Brewer’s sparrow (-3.1%), American coot (-3%), and house sparrow (-2.8%). The lark and sparrow are both primarily in our arid sagebrush country. A number of species in those habitats have been declining, and we suspect the effects of wildfire and weed invasion.
The American coot is one of the most widespread species on wetlands in the West. They seem to be on every pond and around the edges of every lake. But they are in that group with the steepest declines and again point to questions of water quantity and quality.
The house sparrow is yet another puzzle. Here’s an old and very widespread invasive species from Europe that seems to chirp from the eaves of every house in America. Why would this species be declining?
Next are killdeer (-2.3%), varied thrush (-2.2%), mourning dove (-2,2%), hermit thrush (-2.2%), belted kingfisher (-2.1%), and ring-necked pheasant (-2.0%). This is a diverse bunch but realize that I list them together here simply because their negative trends are similar. This implies nothing about their habitats or causes of decline.
The killdeer is yet another declining wetland species, although their definition of “wetland” includes persistent puddles in parking lots. We have probably all seen them nesting in hostile spots, that include too much traffic and too many people. Maybe this tolerance for human activity is finally catching up with them. I hope not. Young killdeer are about the cutest things on the planet!
Varied and hermit thrushes are both species of dense forest. We have hermit thrushes at higher elevations around here — Bogus Basin and forests along the upper Payette River — but you have to go quite far north in the state to get into varied thrushes. They are birds of the big Northwest Forests and don’t like the drier stuff we have around here. They show up rarely in winter in the Treasure Valley. Note that the other deep forest thrush — Swainson’s thrush — is neither increasing nor decreasing.
A lot of people have wondered if Eurasian collared-doves are having a negative impact on our native mourning doves. I’ve not seen nor heard of a good cause-effect relationship here, but maybe. As with most conservation problems, we often need new, targeted research to figure out what’s going on.
A downward trend in belted kingfisher is also head-scratching. They are regularly seen on the Boise River at any time of the year, and it’s not unusual to hear one flying over at some distance from the river. Here’s another species that seems able to deal with all sorts of human activity. But, as with the killdeer, maybe there are limits to what they can tolerate.
The loss of pheasants may be the easiest to understand. As we replace more and more agricultural ground with houses and other urban development, pheasants, gray partridge, and California quail are going to be impacted. But note that neither of the last two species has a significant trend in either direction.
The last three declining species I want to address today are barn swallow, black-billed magpie, and American kestrel, all declining at -1.9% per year. These three species are all reasonably adapted to human impacts and activities. I see them all in my neighborhood in NW Boise on a regular basis. Barn swallows migrate as far as Tierra del Fuego while the magpie and kestrel are residents. Due to these facts and their different ecologies, you have to think the causes of declines are different in each case. Nature is so messy.
The Peregrine Fund created The American Kestrel Partnership (kestrel.peregrinefund.org) in 2012 to try to understand what’s going on with our smallest falcon. This is the sort of partnership that is needed for every declining species. Obtaining more detailed information from many geographic locations and conducting focused research has worked for peregrine falcons, bald eagles, Kirtland’s warblers, and many other species.
Partners in Flight plans in 2004 and 2016 have provided conservation assessments for 448 species of landbirds at the continental scale (partnersinflight.org). So, leaving waterbirds on the sideline for now, do any of Idaho’s declining landbirds make it on the Watch List as of the 2016 plan?
It turns out that the only Idaho species on the Red Watch List — those species in most trouble — is the black rosy-finch. You might wonder why I haven’t mentioned this gorgeous species yet. That’s because it breeds on the alpine tundra where there are no BBS routes. The other factors — small range, small population size, and high threats due to global warming — put the rosy-finch in this unfortunate category. Population trend data must come from Christmas Bird Counts, specialized alpine surveys, or some other source. Or maybe there aren’t any population data.
Other high priority species listed by PIF and found in Idaho include the flammulated owl, mountain quail, and greater sage-grouse. Again, none of these birds are tracked by the Breeding Bird Survey.
The last two species on the PIF Watch List are Cassin’s finch and evening grosbeak. These species are stable in Idaho. Our state is blessed with a huge amount of relatively natural habitat, a low human population, and a lot of public land where these forest finches can live. I think these factors work together to ensure that many of our bird populations are doing relatively well. Once again, this is another hypothesis that needs testing.