Laura Erickson's For the Birds

Monday, October 10, 2011

Where are the birds?

Evening Grosbeak
(Transcript of today's and tomorrow's For the Birds.)

People have been asking me for years why they seem to see fewer birds than they used to. This year I’ve heard from more people, from more places, asking this question than ever before.

To non-birders, birds seem plenty common—often too abundant. Canada Geese, Ring-billed Gulls, and American Robins have undergone something of a population explosion in recent decades. City pigeons, starlings, and House Sparrows are plenty common enough, at least in North America. Wild Turkeys are now found in areas where they never had been found in past decades or centuries, though many local populations aren’t truly established but continually augmented by hunting groups. I’m afraid in the future, Wild Turkeys may become every bit as much of an ecological hazard as white-tailed deer are now.

Wild Turkey

But meanwhile, a great many other birds are declining, some so significantly that we may face extinctions and dramatic extirpations in coming decades unless something is done. Sadly, the birds declining are species never mentioned in school science programs, and many educated adults have never heard of them, so Midwestern children have a more visceral reaction when they hear about impending extinctions of polar bears or penguins or the rainforest than they do about the plight of prairie-chickens or Upland Sandpipers.

Greater Prairie-Chicken

But those of us who have been watching birds for a few decades can’t help but have noticed that before the 80s, we’d see spring warbler waves just about anytime we went out in May, while now even in major migration areas we just don’t see them as often as we used to. Evening Grosbeaks were abundant in the northland during the 70s and 80s—I used to get hundreds every day in late summer every year. This year I had a flock of about 16 stay in my area for almost 6 weeks. This was the first time in over a decade that I had more than one at my feeder at a time, and the first time in at least 15 years that grosbeaks remained here for longer than a few minutes. It was so exceptional that it literally made the newspaper.

Evening Grosbeak

With many declines, we have no idea what’s going on. In the case of Evening Grosbeaks, there is no hard and fast data about their abundance before the 70s, so we don’t know if populations may undergo long term cyclic declines and surges, or if the widespread decline since the 90s, documented over the entire eastern half of the continent, has been truly cataclysmic.

Species by species, we have to tease out the real losses from the apparent losses, to ensure that birds that are missing from one area haven’t simply moved on to another area. There have always been hurricanes, fires, and other catastrophes, and during human history, most species have rebounded after declines. Is it possible that some birds will reach the tipping point due to some combination of the changes in climate, pesticide loads and levels of other toxins, loss of habitat, outright mortality to windows, lighted communications towers, domesticated cats, and all the other changes people have wrought? And will we have enough warning to be able to prevent species losses?

Tower farm in Duluth

That’s all impossible to say. But tomorrow I’ll be talking about how difficult it is for scientists to quantify how many birds have already disappeared.


Yesterday I talked about declines in birds that used to be common in the upper Midwest. Our best tool for quantifying breeding birds is the Breeding Bird Survey, which was started in 1966 by one of my heroes, Chandler Robbins of the US Fish and Wildlife Service.

Chandler Robbins in Guatemala

There are 3700 roadside survey routes in the United States and Canada. Each one is 24.5 miles long, with 50 stops, each exactly one half mile apart. Participants run their route beginning at a set time before dawn on a reasonably calm, non-rainy day in June, pulling over at each stop to count every bird they see or hear in a three-minute period. Usually the participant has an assistant who writes down all the data. Obviously, some of the birds seen or heard are simply passing through, and many birds aren’t detected at all, but over time, because each route is run in the same sequence by the same experienced counters, these routes provide an excellent index of the number of birds holding territories along each route.

Breeding Bird Survey

But the Breeding Bird Survey has some serious drawbacks. First, these roadside surveys are rerouted when necessary as various roads become more heavily used and thus more dangerous. My own route was rerouted as the dirt road it originally ran along was paved and got too busy. As necessary as this was, little by little rerouting compromises the data, because the routes were originally selected randomly, but now are skewing toward less developed areas and bird species less likely to associate with people.

Equally troublesome, the Breeding Bird Survey protocol is to count every singing bird, so a very high percentage of all the birds counted are breeding males on territory. This is exactly what the survey is designed to do, but there is no way of assessing how many floaters—that is, “extra” birds that don’t have available territories so aren’t singing—are out there. Of course, those birds quietly waiting in the wings are pretty much impossible to detect no matter what we do. But there is really good evidence that there used to be a lot of these floaters out there, and there probably aren’t nearly as many anymore. In his 1945 text, Modern Bird Study, Ludlow Griscom wrote:

An acquaintance of mine made a very interesting but somewhat cruel experiment some years ago with the Indigo Bunting. Finding a nesting pair near his house, he proceeded to shoot the male. The next day, the female had secured another male that sang in the same territory claimed by the first mate. He proceeded to shoot the second male. This kept on until he had shot nine different male Indigo Buntings, and he left the tenth male to help the female raise her family.
Griscom’s report predates the modern study of floaters—he was simply using this as an example of female songbirds being fickle. But it is an excellent example of a small study area in which at least nine males were present who were not detected until the male on the territory was removed.

Indigo Bunting

Unfortunately, we have no way of knowing how old these males were. Current studies of Indigo Buntings indicate that virtually all males more than a year old have mates. Did there used to be a lot more males in the 1940s than there are now? There is no way of knowing for sure.

But Sydney Gauthreaux of Clemson University learned to analyze NEXRAD radar data to detect bird movements. He found that between the mid 1960s and the mid 1980s, the number of significant spring migration flights detected from his study area along the Gulf of Mexico had declined by almost 50 percent. He found a similar loss between the 80s and the new millennium. Although these are astounding numbers, and some scientists have questioned his techniques because the numbers don’t jibe with Breeding Bird Survey results, the truth is that his is the only objective data we have quantifying raw numbers of trans-Gulf migrants, including both floaters and breeding birds. Floaters provide an essential backup reserve population. I’m afraid we may be losing far more than people want to face. I hate doomsday reports, but unless we face bird declines square on, how can we possibly avert doomsday?