My very first job abroad – the sort that requires you live somewhere other than your own home – was working as a nest-searcher in the Sierra Nevada mountains of the Lake Tahoe Basin in California/Nevada. Aside from a little bit of homesickness, it was an amazing summer. I drove down from Ontario at the end of April, taking the opportunity to do a bit of birding along the way as it was my first cross-country trip on my own. When I got there many of our study sites still had up to a foot of snow in the valleys and north slopes. Even in July, when we went out in the mornings I’d wear my winter jacket, toque and mittens, shedding layers as the sun came up till by the time we went home in early afternoon I’d stripped down to a tank top. I spent three months getting up an hour or more before dawn and trekking about the mountain slopes, hunting for birds’ nests while my partner (we went out in twos) spot-mapped the birds at the site. At the end of the season I led the team in number of nests found, a fact I’m still a little bit proud of, though its useful application is rather limited.
I still do a bit of nest searching in the summer, but nest searching requires time and patience. The most effective technique I found for locating nests is simply sitting in one place for a while and watching the birds come and go. When you notice one carrying nesting material or food, you can (stealthily) follow where it goes. Likewise, you might notice a bird repeatedly leaving a particular shrub or tree branch, which you can then go search. It’s also usually best if you don’t have a wolf-shaped animal cavorting about the area where you plan to sit and watch. So my opportunities for nest-searching are usually limited to my time between net-checks during our MAPS visits.
Nest searching is immensely easier in the winter, at least for those elevated from the ground. For one, you can bring your wolf-shaped animal with you, and no one’s going to care.
For two, after the leaves come down the bulky shapes of nests tucked into the twiggy vegetation are easy to spot, once you’ve got the search image in your mind. Even easier if they’re topped by a contrasting white hat of snow.
In our second field, halfway back on the property, there are several large patches of steeplebush and Rubus brambles (the short, thick stuff in the foreground of the first photo). The Field Sparrows like to nest in these, and I noticed the snow-capped construction of one pair while I was out snowshoeing the other day. Despite the leaves being down, if you’re not actively looking for them, it can be easy to overlook small nests, and I hadn’t paid any attention to the steeplebush patches. Curious, I wondered how many I could find.
The answer was four. It’s interesting that while each nest is very similar to the others, they’re all a little different, too. There’s always the possibility that one might have belonged to another species, but there are few other species that use that habitat, and which would also be likely to place their nest in the steeplebush. So I think these are all Field Sparrows.
Identifying birds’ nests can be a challenge. You think it ought to be easy, because it’s true that different species have different building tendencies for shapes and content, but there’s often a lot of overlap between species of the same taxon, and within a species different individuals may build differently according to what materials they have on hand and where they decided to place the nest. The nests of some birds, like robins (which always line their cups with mud), are easy. Baltimore Oriole nests (which are pendulous pouches of grass suspended from the ends of branches) are easy. Sparrows are tricky, as are warblers.
Most sparrows build cup nests, either on the ground or slightly elevated (none of these were above mid-thigh). They typically have exteriors of coarse grasses (or reeds, where the species lives in wetter areas), with interiors lined with fine grasses, rootlets or animal hair. Chipping Sparrows, for instance, almost invariably line with coarse hair, in my experience. Field Sparrows usually use fine grasses. So sometimes knocking off the snow cap and taking a peek inside can help to clear up an ID.
By the time you reach mid-winter, identification hasn’t been helped by the weathering process. Nests often look like they’ve gone through the washing machine one too many times. Many are misshapen; in others the materials have started to fall apart, or have become stuck together with repeated soaking. American Goldfinches, Yellow Warblers and Willow Flycatchers, which use plant down in the construction of their nests, tend to suffer this latter problem. This nest might have been a poorly-built Field Sparrow nest. Or it might have belonged to something else entirely.
This one had a flattened top, when I knocked away the snow. It puzzled me. Was it simply a nest where the cup part had been compressed under the snow? Perhaps it was a nest that had been started, but never finished? Another possibility that struck me was that it might belong to a species that builds covered nests. If this were in a wetland, I might suspect it to be just such a thing – Common Yellowthroats, for instance, build covered nests elevated in the cattails. But this was in a meadow, in a steeplebush. Besides, when I gently worked it free from the bush it was sitting in, I could see no discernible entrance. Odd that it would appear flattened when the others were all still intact, though.
This last one was slightly away from the others, further up the field, and placed in a hawthorn instead of a steeplebush. It would serve as good protection, I’d think! The construction was similar, though, and I’m pretty sure it’s another Field Sparrow. They’re not too particular about their substrate: hawthorn, spruce, pine, juniper, elm, apple and white cedar are listed as the most common substrate species in the book Breeding Birds of Ontario: Nidiology and Distribution by Peck and James.
If you can find yourself a copy of that book, incidentally, you should snatch it up. It’s out of print, but copies still float around. It’s essentially a summary of the data from the Ontario Nest Records Scheme from the 1960s through 1980s. It’s published in two volumes, Vol 1: Nonpasserines, and Vol 2: Passerines. The intro to #2 states that the book covers 144 species, using data from 67,091 nest records from around the province. They also incorporate external data into their species summaries, which are thorough, and usually list all variations and peculiarities reported. They mention everything from habitat, microhabitat, substrate preference, location within substrate, height, nest measurements, structure composition, egg dates and clutch sizes, to cowbird parasitism rates… and more. Almost 25 years have passed since its publication, but its still entirely applicable. An amazing resource.
It’s funny to think that those nests were there all summer, and all summer I simply walked by them, never knowing. I think this year I’ll need to try checking out the brush patches to see if I can locate any while they’re still active.