Junco-induced bipolarity

So far this season we’ve caught at least one bird every day. Most days we catch two or three; our best days have been our three five-junco days. This season is going really well.

Yet, at least every other day I find myself thinking, “This is it—the beginning of the juncos’ ceasing to respond to us, the moment where we lose our mist netting mojo.” It’s amazing how crushing it can be to go hours not catching a bird. Never mind how many you caught yesterday—this is the turning point, the day it all stopped working.

Then you catch a junco, finally, and everything is great!

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Brood patches: birds bare their midriffs

Almost all birds incubate their eggs: keeping them warm while the embryo develops into a chick. In order to transfer heat better from their body to the eggs, many birds develop brood patches (a.k.a. incubation patches). The bird loses feathers from her belly, and the bare skin becomes wrinkly and swollen with fluid. In juncos only the female develops a brood patch, since she does all the incubating, but in species where males also incubate, males can develop brood patches too.

White-crowned Sparrow with a brood patch that is beginning to show edema

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Meet LAGG (Lime – Aluminum – Green – Green).


He lives a good 30-minute walk from a campground off Highway 120, far from any other junco territory, as seems to be the rule in our low-elevation sites. We did not see a mate with him—which is strange, to me, because from my subjective human perspective I think he is the handsomest male junco we have caught so far. His head is stark black, no brown feather edges; his back is a rusty red-brown; his tail feathers have lots of white. But of course, there’s no reason to think that female juncos have the same taste in male juncos that I do—and that’s one of the things I’m hoping to find out: what aspects of junco appearance matter to female juncos?

So handsome!


Meet SNAG (his leg bands are Sky blue – browN – Aluminum – Green). He lives at approx. 3100 ft above sea level, in a campground along Highway 120 in Stanislaus National Forest. He seems to be doing well: he has a mate, and when I say he lives in a campground, well… actually his territory appears to encompass the entire campground!


His mass is about normal for what we’ve been seeing – 17.6 grams – and he has no visible subcutaneous fat, like most of the juncos we’ve caught. So he’s probably fine, but he could stand to eat more. And he’s working on it: when we caught him he had prey in his bill! They look like aphids to me, but I haven’t really tried to identify them yet.

Eight angry juncos

In the mid-elevation sites we visited last week, juncos were reliably everywhere. The challenge was luring them into the nets.

Not so in the low-elevation sites we just visited. We spent most of our time looking for juncos; once we found them, we had them in the nets sometimes within thirty seconds of starting playback. This was the land of the few aggressive juncos.

SALO, the first low-elevation junco we caught

At three sites we found just eight juncos, compared to eighteen at the three mid-elevation sites. This is not an elevational difference I anticipated, which is neat!