Tuesday, July 8, 2008

Thumbs up for rules of thumb

Sulphur-crested Cockatoo shows its colours at Tyto

THUMBS up or thumbs down for rules of thumb? By and large my birding thumb figures on a species count of 60:90:120 at Tyto. That's 60 birds in a full morning, 90 in a week, and 120 in a month. That's a big month.
For a quieter month the figures are 50:80:110. The thumb hasn't got a figure for year by year counts, the task being too much to grasp. And that's the problem you can put your finger on with rules of thumb: lack of precision. Lately, 60 has been a push, 90 too low, 120 about right. Thumb's still sort of up ... for now.
Here's a bit of even more relevant arithmetic. Tyto species list still stands at 234 after latest addition (Red-capped Robin) and a subtraction (Gould's Bronze Cuckoo, swallowed by Little Bronze Cuckoo). After several 120-bird months how many of the 234 should be seen? Don't rush to answer.
First, subtract the singleton sightings and the species not seen in the last four years. That's 25 off the list. Now delete the rare and the rarely seen: goodbye to another 42. Throw in seven more as extremely unlikely and the number is a rounded 160. Allow for seasonal migration and influence, and at this quarter of year another 20 (rounded) vanish. Down to 140.
Guess what? Just checked, and found my count for April-May-June is 140. Another rule of thumb in the making!
So far, so boring, you say? But there are a couple of points to be taken from the figures. The first has been made in earlier posts, perhaps without much support info. It is: take a cold, hard look at all bird lists. Second: seek local knowledge.
Surely the second point needs not be stated? Oh, but it does, indeed it does. Many well-travelled birding tourists give the impression they would prefer to miss sightings than be thought in need of help from anyone (not just me!).
Just as strangely, travellers frequently stand in the midst of Tyto's plenty and persist in talking only of their (often Northern Hemisphere) stamping grounds. That this is so literally out-of-place and wholly upsidedown seems to escape them. Tourists, OK; bore-ists, no!

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