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Christmas Bird Count trends

American Kestrel
Mark Faherty
/
American Kestrel

Every year around this time I can be heard carrying on about the Christmas Bird Counts – which rare birds were seen where, what count had the most species, and so on. This “sports page” account of the counts is fun way to look at it, but it doesn’t mean much in the big picture. This is a long-term data set, one that deserves a longer view.

For over 120 years now, birders have ventured out on winter days to attempt a tally of all the birds – not just the sexy species birders chase, but literally every chickadee and pigeon within a 15-mile circle. The resulting data has been invaluable to countless researchers and studies. Mass Audubon used it as one of the three main data sources for our State of the Birds report, and it factored heavily into that “3 Billion Birds” study that everyone was talking about a few years ago, the one that said we’ve lost that many birds in North America since 1970. So what are the results saying about birds here on the Cape and Islands? Let’s take a look at some local winners and losers who show clear trends in the Christmas Bird Count data.

First, the bad news. Several formerly abundant species show plummeting trendlines over recent decades. American Kestrels, those colorful little falcons of grasslands, are all but gone as wintering and breeding birds in our region. Theories include loss of habitat, as former open land has grown into forest, as well as the increase in a predator of theirs, Cooper’s Hawks (spoiler alert, they are one of the big increases).

Long-tailed Ducks, an arctic nesting species that very recently wintered in Nantucket Sound by the hundreds of thousands, has largely disappeared. They’re not hard to find, but the old days when great clouds of these speedy little ducks rocketed past the west end of Nantucket seem to be gone, at least for now. The reasons are mysterious, maybe a decline in a favored food source south of Nantucket, where they apparently ate small invertebrates in the water column, things like amphipods. Or perhaps climate change has screwed up their short breeding window on the Arctic tundra, where planetary warming is greatest.

Then there are Northern mockingbirds, those Broadway-style suburban songsters, who’ve shown a steep and puzzling decline, not just here but across their range. Mockingbirds don’t migrate, so should benefit from the now milder winters, and had already benefited from all the persistent, non-native winter fruits we’ve added to the landscape, like multiflora rose and bittersweet. Those food plants have certainly not declined, so why have mockingbirds? I suspect neater farming practices, plus an overall decline in farmland across the east, is partly to blame. One off-Cape farm I visit each year on a Christmas Count used to have several mockingbirds throughout the tangly hedgerows between the fields. The owners recently bulldozed the hedgerows, and now I’m lucky to find one.

Mockingbird
Mark Faherty
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Mockingbird

Believe it or not, our humble, sometimes hated Herring Gulls have shown one of the steepest declines of any species in the east, about 5% per year. Us bird people always say it’s probably because they closed most of the landfills and there aren’t as many fishing boats, but their primary nesting island, North Monomoy in Chatham, is also eroding away. But don’t panic, gull lovers, as the decline is most likely a return to natural population levels after being unnaturally high from all the artificial food sources at the dumps and piers.

And now, finally, for the good news! Actually, I have some bad news — I don’t have time for the good news. So we’ll definitely get to the increasing birds next time. Probably, we’ll probably get the increasing birds next time. You know, unless there’s more interesting bird news to cover. Or if I forget. But I will definitely, possibly get to the increasing birds next week.

Mark Faherty writes the Weekly Bird Report.