Monday, December 8, 2014

Lark Buntings in the Tucson Valley CBC

Guest post by Rich Hoyer, TVCBC Compiler
A recent eBird submission for Lark Bunting at Rio Vista Natural Resource Park got me to thinking. This park is only a mile from where I live in north-central Tucson, and I’ve seen the species in this neighborhood only once in the more than 17 years I’ve lived here. Then it occurred to me that we’ve missed it on several recent Tucson Valley Christmas Bird Counts (happening this weekend, Dec. 14!), including last year’s record-breaking species count. But has it always been a difficult bird here?

Lark Bunting at Rio Vista Natural Resource Park found and photographed by Joan Gellatly.
I was surprised at what I discovered when I looked at the data since Tucson Valley’s current circle was described in 1971. The most surprising is what has happened only since the late 1990’s. Our Lark Buntings have all but disappeared, and they used to be annual, sometimes in the thousands.

This quick blog can’t begin to investigate what might be the causes of this decline, but we can rule out lack of observer coverage. The graph I generated actually accounts for observer coverage by dividing the number of birds by the number of total hours birders spent in the field, the simplest bit of statistical work you can do with these numbers.

To start, one might look at local and regional changes in habitat availability (maybe we’ve lost the habitat they prefer). I did look at about 17 years of area-by-area data, and when they were most abundant, Lark Buntings were found all over the circle, presumably in the larger washes. But they were in the Rillito Wash, way up to where Pantano and Tanque Verde join. They were often in the CaƱada del Oro. And most regularly they were along the Santa Cruz River. At least the latter of these has changed drastically since the mid 1990’s.

Or perhaps one might look at larger scale changes in habitat use and distribution (maybe there’s some other area that is now much more superior where they now prefer to winter). But perhaps most telling might be to look at other CBCs and census data to determine if there’s been a overall decline in the entire population that is mirrored in our CBC data.

But this example shows at least that while nearly all of us are participating in a Christmas Bird Count because it’s fun, relatively common, easy-to-observe, and easy-to-identify birds actually produce some useful data. It’s nice to know that our birding habits might leave a legacy.

Contact Rich Hoyer to sign up for the Tucson Valley CBC. Learn more about the count here:

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