Sunday, August 23, 2009

On Bird Populations

Boy am I frustrated! I just spent a couple of hours making yet another list of local birds and trying to figure out which ones I'm likely to see at which time of year and whether their numbers are large or small here. I mostly have fun with these lists, until you start playing with the population numbers.

Here is what I've done so far. I've used about 5 field guides and made an entire Excel spreadsheet for every bird that field guide range maps have for right where I'm located. This is a good general guide of what may be here. The problem with those maps is that the entire colored area does not all contain that particular species.

So months ago I decided I wanted a more localized view of bird populations. Voila, the NY Breeding Bird Atlas! This is a fantastic tool. You can narrow down to counties in NY to see if it's been confirmed that a bird has breeded in that county, or two levels of maybe. There's an older BBA for NY that you can compare with as well. You can see population trends over time for BREEDING birds in NY and the likelihood that you are going to see that species in your particular county. You can also the species abundance throughout the state in general. I took all this info and kept notes on which birds seem to have big populations, medium-sized ones, and low numbers in my counties (I bird in 3). I also made notes on if the population was increasing, stabilized, or decreasing over time. I have found that it is useful maybe 70% of the time that I look at it. That's right, it's not 100% (though one can say that about all data). I see here and there where it states that it is used to determine population trends, period. That's it. No "population trends of BREEDING birds."

You might be asking yourself, "Well, what's wrong with that?" Well, it leaves out our winter birds, the species who come down from Canada during periods of deep snow to find food. They don't breed here! So they either wind up completely missed from the BBA, or the BBA inaccurately shows on the map that it seems to be a rare species. This does not help the birder that is simply trying to determine the likelihood of seeing said winter bird friends. And field guide range maps are even worse at figuring that out.

Also, I noticed that the Ring-billed Gull, while on the BBA, seems to have an incredibly low population, to the point of probably being considered a rare. Well, I've taken part in PA BBA point counts. Point counts tend to be held in nice natural areas away from mankind. Where are these gulls? Shores, parking lots, picking around garbage bins...these are not really point count spots. They certainly do breed in my counties. I sometimes see them in numbers up to 20, looking for fries. I doubt they have low population numbers, and Peterson notes them as "common."

And then there are just those birds that are locally common, irruptive, or need a very specific habitat, or have populations that have declined so rapidly so quickly that data collection can't even keep up. Many, many of our winter birds are irruptive. Last year we had a nasty winter, and pine siskins came down in droves. We could see nearly no pine siskins this coming winter, especially if it's mild.

Maybe I would have better luck using ebird data. Ebird, a site by birders, for birders. It relies only on whether a species was seen during a certain time period, rather than if it was having sexytime or not. The immediate problem I can see there is if an area is lacking in birders.

But for now, nothing seems to be able to explain why I am not seeing the apparently common northern flicker ANYWHERE.

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