Sunday, December 26, 2010

Counting Birds

Rock Pigeon
Rock Pigeons came to North America with the early colonists. They swirl in clouds over towns and cities. They fill ridge lines and cornices of buildings. They find crevices and ledges for nests. Their highly acidic excrement hastens corrosion of metal and deterioration of stonework. They are viewed often as urban pests, rats on wings.

House Sparrows were released in New York City in 1850. By 1910 they had spread to California, filling empty spaces with their toneless songs, finding food in horse barns, feed stores, urban and town streets. Sometimes the only bird in a barren city landscape, these nondescript birds often appear as dingy as their habitat.

European Starling
European Starlings were released in New York City in 1890. An industrialist with too much money and too little sense wanted the city park to be filled with all the birds mentioned by William Shakespeare. Within thirty years, starlings were common throughout the eastern United States, and they kept spreading across the continent. Winter flocks fill trees, noisily clicking and clacking and rattling. They ball up in huge dark clouds over barren fields.

A few people like these birds. They throw bread crumbs to pigeons in parks or see the House Sparrow as the only bird which comes to their city bird feeder. Many more people do not like these birds. They are invasive exotics. Birders don’t like them. Public health officials and city building owners who must fight the effects of their guano don’t like them.

I confess to a grudging admiration for these birds. In North America, they have adapted, often to harsh habitats created by humans - like barren towns and cities where they survive by feeding on our garbage.

For the most part, they have also hit an ecological balance. Admittedly, the numbers of pigeons, starlings and House Sparrows often approach “hoard” status. But, the population of any species fluctuates, and over time that fluctuation is proscribed by what their habitat can support.

House Sparrow
If there were no controls on the population of these invasive exotics, I would expect that their numbers would increase year after year. But that is not happening. My evidence is the Christmas Bird Count.

In the Brattleboro area, the CBC for pigeons, starlings, and House Sparrows varies from year to year, sometimes dramatically. Nevertheless, over the last several years, there is some consistency. The pigeon count has ranged from a low of 133 to a high of 414 with an average of 282. Starlings have ranged from 165 to 640, with an average of 347. House Sparrows have ranged from 72 to 299 and average 199. Year to year differences might be explained by whether the counters saw the flocks during their count day and how adept they were at counting large numbers in flight or roosting. What is clear is that there is no upward trend, and for that matter, no pattern or trend of any sort that I can see or imagine. These invasive exotics are here to stay, but it also appears that they  have found their habitat balance.

This is a long introduction to the Brattleboro Area CBC which was done last Saturday. Looking at count results over a period of years shows that this not just a day long exercise by a bunch of bird nerds. As teams of counters cover the same area and employ consistent methods, data is gathered. That data can then be gleaned for information. I have just given an example of what the data might be telling us about the exotic species.

Red-bellied Woodpecker
The date also tells us that the Red-bellied Woodpecker which began to show up on CBCs in the early 1990s is now a well-established resident, on its way to becoming relatively common. The last three years have been the highest count years for this species, with this year the highest.

The Red-bellied Woodpecker is the most recent of the southern species to extend its range northward and establish itself as a year-round resident. It was preceded by the Northern Cardinal, Tufted Titmouse, Northern Mockingbird, and Carolina Wren. The data also suggests that the Carolina Wren is the most tenuous of these southern species that have moved northward.

The CBC confirms the success of some conservation efforts, habitat improvements, and species recovery.

Common Raven
“Cur-ruk, cur-ruk” from the Common Raven was silent 50 years ago in the West River Valley and surrounding hills. It reappeared on CBCs in the early 80s. Ten ravens were recorded on the CBC this year, a record.

The Bald Eagle, absent on CBCs prior to 2002, is now consistently observed. The breeding pair in the vicinity of the Vernon Dam have open water through the winter in which to fish, and remain on territory.

The Wild Turkey was extirpated from most of New England my the mid-1800s. In 1970 they were reintroduced in Vermont. Winter flocks are nomadic and CBC numbers fluctuate wildly, but they are consistently recorded.

Eastern Bluebird
The Eastern Bluebird were absent from the CBC until 1992. Since 2000, this species has been recorded every year on the count. It may not be common during the winter, but no one should be surprised to see a bluebird during any month.

Finally - American Robin. People are often surprised to see the robin in winter. Don’t be. They are present on the CBC every year, and may be seen any month of the year.

The Brattleboro Area CBC had 32 people in 7 teams doing the field counts. Additional people did feeder counts at their homes. Collectively, the seven teams drove 280 miles, walked an additional six miles, and logged 185 people hours. Unlike so many years, it was a delightful winter day, with brilliant blue skies,  pleasant winter temperatures, only a dusting of snow, and only a few icy spots when walking. It made for a day of good birding.


eileeninmd said...

Great post, Chris! It is interesting to see how the populations are changing over the years. I love that the bluebird is making a comeback.

Bill S. said...

Very interesting post. Sometimes I think counters get tired of trying to get a count of the huge flocks of Starlings. English sparrows and pigeons are the victoms of the small raptors that inhabit the towns and cities.

Merry Christmas.

Larry said...

I enjoyed the post-especially about the non-native species.I don't hate them but I guess that I'm more of a birdwatcher than a birder. People introduce new species of birds here and then despise the birds-why? It isn't the birds fault. They may not be my favorite species to see but I'm not bothered by the sight of them.

Andy said...

A good read


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