bird nests

Nest searching

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.

The summer homes of vireos

It’s amazing just how much more you can see once the leaves drop from the trees. And I don’t just mean the neighbours. Walking down the same trails you walked every day in the summer you discover things that you walked right by a hundred times and never noticed while they were hidden by leaves. The above is a great example. Hidden while the trees were leafed out, once the branches were bare the pale blob in the small sapling shone in the winter sun, clearly visible from the other side of the meadow. While the snow was deep I chose not to walk over, but once it had melted enough I made my way across in order to check it out more closely.

It turned out to be a nest, but then, I was pretty sure it was a nest. What I was surprised by was the amount of birch bark woven into it, the pale material that made it glow so vibrantly. The nest belonged to a vireo, who make characteristic open cup nests suspended from a branch by their rim, rather than perched on top of the branch. Vireos are the only species around here that build nests like this; the other species that build suspended nests (eg. Baltimore Oriole) have structures that are closed at the top, with an entrance hole in the side. It amazes me, really, that a vireo’s nest can be strong enough even when suspended by the rim that it supports four or five little growing bodies crammed in there together. I would have thought that the branch underneath would lend necessary structural support, but apparently the birds are such skillful weavers that even without glue or stitching their constructions will hold a full family, and then still last through the entire winter.

Although I know it belongs to a vireo, it’s harder to be certain of which vireo. I’m actually reasonably sure that this one was built by a Red-eyed Vireo, who are known for using a lot of birch bark in the construction of the nest’s exterior. They also have a tendency to favour younger trees, thus building lower to the ground (although I had to climb this sapling in order to reach and pull down the branch it was in, it was still less than 10 ft high), and aren’t opposed to nesting along forest edges. They would also be extremely abundant through our area.

This nest (can you see it?) was less than 100m away from the first one. It was also built low, perhaps 8 feet above the ground. It was also at the edge of the woods, but the area it faced on to was an open treed space rather than a meadow. The tree it was in was a tall mature maple, and the nest was just in a low horizontal branch. Even with the leaves gone, it’s still somewhat tricky to spot, blending in with the surrounding branches, unlike the first nest.

The identity of this nest-builder is less definitive. That’s the frustrating thing about nests in winter; so many are very ambiguous and you can’t be sure just who built it. Sometimes it’s tricky to even narrow it down to family (eg. sparrow vs warbler). At least I’m confident about that part in this case; it’s clearly a vireo. We haven’t been here for the breeding season yet, so we don’t know which species we have in our woods, although we have a pretty good idea of what to expect. At the very least we have Red-eyed and Yellow-throated Vireos here. We may have Blue-headed, too, if we’re lucky. There’s undoubtedly Warbling around in the riparian areas, along the beaver meadows and creek edges, but they wouldn’t be found in the forest. Blue-headeds nearly always build their nests in coniferous trees, so I very much doubt that this nest would be by them, even if we do have them in our area. Which leaves Yellow-throated and Red-eyed.

The odds-on favourite is for another Red-eyed, simply because they outnumber the Yellow-throateds by about 65 to 1 in the Kingston region (in other parts of Ontario, this ratio is even higher; this is probably the best area in Ontario, and likely equal to many parts of the US, in terms of the proportion of Yellow-throateds in the vireo population). The book Birds of the Kingston Region by Ron Weir estimates one pair of Red-eyes per hectare (2.5 acres) in our area, so the proximity to the other nest might not be unusual. Also, Yellow-throateds have tendency to build high up in mature deciduous trees, so this would be unusually low. That said, however, the Ontario Nest Record Scheme has records of Yellow-throated nests as low as 4 ft, so it wouldn’t be unheard of. Mainly the only reason I would consider the possibility of Yellow-throated, really, is the relative absence of birch bark in the exterior, as they use less of it than Red-eyes usually do. But who’s to say this isn’t just a Red-eye with slightly different aesthetic tastes.

I took these photos a couple of weeks ago (hence all the snow on the ground; most of it’s melted now), but was reminded of them by a post by Huckleberry Days on a nest of mysterious identity. Bird nests are one of those typically winter topics, because you tend to see so many of them at that time of year, compared to in the summer when they’re usually more hidden (unless you’re actively looking for them). I stored up a few photos, but hadn’t got to writing about it. I’ve been amazed at how the winter has flown by – and suddenly, spring is upon us and I’ll have no shortage of blog material for another eight months!

Seasonal waterfront homes

Following a week of sub-freezing temperatures, Kingsford Lake is now completely iced over from shore to shore. The lake is shallow, actually mostly man-made in that it started out life a hundred years ago as a small lake on a river. The river was dammed and the shallow river basin and surrounding floodplain flooded to form the lake. Most of the lake is ten feet deep at most, with just the original small lake being very deep. Because the lake is so shallow, it freezes quickly, and even the small current that still exists along the river’s original bed, which stayed open till the last, is now solidly closed up.

We haven’t been able to cross to the other side of the lake for about a month, since ice started to form on the water and we pulled the boat up onto shore. Today, we took Raven and headed out across the ice to wander about the lake. We headed first to the island that’s in the centre of my blog header, on the east side of the lake. Dan wanted to look for owls there, but with so much habitat available to them we didn’t find any while we were out. From there we crossed back over the open expanse of the lake to the west shore, our second destination the large marshes that fill in the shallow western bays.

While the water was open we weren’t able to go in here; the water was sufficiently shallow, and the lily pads and pond weeds sufficiently dense, as to prevent any sort of meaningful boat traffic through the area. It might be possible in the spring and early summer for me to bring my canoe over, which would be a little more maneuverable than the punt boat, the water level should be higher then, and the plant life won’t have begun to fill in yet.

Now that the water has frozen over, however, we can easily walk among the cattails. Dan commented that he thought it might be the first time he’s actually walked through a marsh. It was a reasonably large wetland, especially for our area where wetlands are sparsely scattered and tend to be small.

The history of the lake is apparent in these shallow areas. There are many aged, weathered stumps, and tangled root masses from dead trees that had toppled over in the softened soil. When the river was dammed this area would have been forest, and much like with beaver ponds, the result of the newly-formed lake was a lot of dead trees. It amazes me that so many of these stumps still persist, given their presumed age.

Some of the root tangles make fabulous natural sculptures. You can see why they really appeal to some people as art pieces (check out these amazing driftwood horses by artist Heather Jansch I found while looking for a driftwood sculptures link; I would love one of these, but where would I put it?).

The cattails in the marsh here appear to be Narrowleaf Cattail, Typha angustifolia, separate from the Common Cattail (or Broadleaf Cattail), T. latifolia. I can’t remember consciously noting unusually narrow cattails before, though I would be surprised if I hadn’t encountered the species prior to now. In the Toronto area I only really recall encountering the latter, certainly the most common cattail species there. Here, everything seemed to be the former species, so far as I could tell from their dead, broken stalks. There were also a few reeds and sedges mixed in with them, but fortunately no sign of the invasive phragmites.

We poked around looking for nests. Nests are definitely easiest to find in the winter, when they become exposed as the vegetation that concealed them in the summer dies back. Many don’t make it through the fall and winter weather, but some that are particularly well-constructed or protected may survive without too much damage. Searching for nests in the marsh is definitely easiest at this time of year, as you can just walk through the dead vegetation looking for dense clumps.

We found five in the area we covered; not as many as I expected considering that Red-winged Blackbirds will probably be dime-a-dozen there come spring, and then you’ll also have other marsh nesters in there as well, but a good collection nonetheless. Most of them looked like this as you approached – a dark mass topped with a distinct white crown of snow. It was hard to tell what you’d found until you approached and brushed the snow off the top to assess the size and shape of the nest. The size of this one, along with the coarseness of the materials used in its construction, leads me to believe it’s one of the many Red-winged Blackbird nests that were probably built there last summer.

Here’s another Red-wing nest. I’ve found, at least in the nests I’ve observed, that they tend to use broader grasses and other materials when they’re building the outside of the nest, giving theirs a distinctly coarse appearance that you don’t really see in other cup-shaped nests of marsh species. I’m always amazed when I look closely at these just how well they’re woven around the supporting vegetation – so snug, you can’t remove it without a pair of scissors to snip off the vertical stalks. A human would require some skill to produce something like this, and a human has opposable thumbs!

This one is a Marsh Wren’s nest. We haven’t observed any Marsh Wrens here since we moved in; they’re most easily detected by their distinctive, chattery mechanical song. By the time of our arrival in August they would have all stopped singing. But here is clear evidence of their presence last summer. Marsh Wrens build domed nests, completely enclosed except for a small wren-sized entrance hole near the top on one side. The interior is deep; if you stick your fingers in one (as I’ve done a few times when checking the contents of an active nest), your fingers will just barely reach the bottom to be able to count the eggs. Not too many species build enclosed nests like this, and as far as marsh nesters go their nest style is unique.

Finally, another cup nest, woven into the cattails and suspended above the water in the manner of the Red-wings. It differed from the blackbird nests, however, in the coarseness of the grass used to construct the outer walls. It’s got a tidier, finer appearance to it, subtle enough that it could possibly just be a fastidious blackbird, but I think it may actually be the nest of a Swamp Sparrow or Common Yellowthroat. I’m leaning toward the latter, based on the wider vegetation woven into it. It resembles this yellowthroat nest to me more than it does this Swamp Sparrow nest.

Whatever it was, the youngsters fledged successfully. How can I tell this? If you look closely, you’ll see some droppings on the rim of the nest. The nest was actually tipped down toward that side, I righted it a bit for the purposes of a good photo. Nestlings, as they’re preparing to take that great leap of faith that will turn them into fledglings, will perch on the rim of the nest. Their weight as they all do this will often cause that lip of the nest to fold down, or sometimes for the whole nest to tip. Also, just before they leave they’ll often poop, a reflexive habit birds have that may perhaps be to “lighten their load” for flight. The presence of droppings on the lowered rim suggests that the youngsters at least made it as far as that stage of life. Hopefully they’ll make it through the winter and we’ll get to see them return come spring.