Your Bird Observations Matter!

By Kevin J. McGowan, Ph.D.

More than ever, we urge you to participate in the Great Backyard Bird Count (GBBC). Rarely have we had such a pressing need to understand the changes in bird populations as we do right now. The introduction of West Nile virus into North America in 1999 and its subsequent spread across most of the continent has been one of the most dramatic recent stories in public health. But what many people do not realize is that this is a more serious wildlife health problem than a human one. Â	Â
West Nile disease appears to kill large numbers of birds, especially American Crows. Just what the full impact of the disease on bird populations has been and will be is difficult to know. The GBBC can help us understand this.	Â	This crow was part of a long-term study of American Crows conducted by Kevin McGowan in the Ithaca, New York, area. It succumbed to West Nile virus in 2003, when it was 13 years old.

Abnormally large numbers of dead birds were the first hint of the new disease on the continent, and the appearance of dead birds (especially crows) is still one of the first signs of a West Nile disease flare-up in an area. Laboratory tests have shown that many different species of birds die from West Nile virus infections. So we know that the disease is killing thousands and thousands of birds. What we do not know is how important this mortality is to any population of birds. Just because we see lots of birds dying does not necessarily mean that the populations will be affected. Millions of birds die each year from a variety of causes. If they don't die of disease, then a predator might get them. If the predator misses them, they might die in a storm as they are migrating over the ocean. And so on. Often the total mortality in a bird population remains remarkably constant from year to year, despite large changes in individual mortality sources. (This principle of 'compensatory mortality' is the basis for sustainable hunting, and allows the sport harvest of more than a million Mallards each year with no negative effects on the overall population.) We need to know if this new disease is an important additional source of mortality, or just another, rather trivial part of the complicated cycle of life and death. At this point we just don't know.

So, are bird populations declining? It turns out that when we look for significant changes in bird populations, we find that not many programs are in place to count many different kinds of birds. And most of the monitoring methods contain so much uncertainty and variation ("noise") that it is difficult to tell if any changes are real ("signal"). One way to distinguish signal from noise is to have a number of different ways of looking at bird populations. If all of the different ways of counting birds give the same answer, then we can put more trust that we are finding a real change (or lack thereof). The Great Backyard Bird Count is one of those additional pieces to the puzzle.  Enough people have been participating for long enough that we can compare years before West Nile with later years to look for an effect.

We then can compare these results with data from Christmas Bird Counts, Project FeederWatch data, and Breeding Bird Surveys to look for trends.

Small, secretive birds such as Eastern such Eastern Screech-Owls are not easy to detect when they've succumbed to diseases such as West Nile virus.

What do people need to do? Should they look specifically for large numbers of the susceptible birds, such as crows? No, they should carry on as usual, duplicating their past efforts as best they can. But they should know that their reports of low numbers of seemingly mundane species are valuable. We want to hear about the most common species. Crows, hawks, and the larger owls have gotten most of the press about West Nile. These are the birds that are most obvious when people find them dead. They're big birds, and people notice them. What about the little, hidden species, like Brown Creepers or screech-owls? If they died in large numbers, who would know? And we really, really want to know if people are not seeing those common species. People have an understandable but rather unfortunate tendency to feel less compelled to submit checklists if they didn't see species that they think are of special interest. In fact, we are most interested in hearing about the common birds. And we are very interested, especially now, in getting reports where species are not seen. We need to know where the real zeros are. If you did not see any crows this year, we want to know about it. Without reports that mention the missing species, we cannot distinguish an unsampled spot on a map from a place where the species of interest is actually missing.

We need to keep sampling bird populations repeatedly and in as may ways as possible so that we can find out the true effects of this disease on the bird populations of North America. The Great Backyard Bird Count is part of the process, and you can help.

For a look at what eBird data are showing about American Crow numbers, read "Fewer American Crows?"

For more information on West Nile virus, go to http://www.audubon.org/bird/wnv/.