Now that the leaves are all gone, I can see many of the nests that Passerine birds built last summer. Many of them are in small brush, fairly close to the ground (one I walked past almost every day last summer without knowing it was there!). Does anyone know if small birds prefer smaller brush to nest in rather than higher in bigger trees? Or this this an observational bias since I can’t see small nests high in trees? And, is it possible to identify nests from photographs? I’m in Winnipeg, Canada.
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Generally, we see that passerines are quite diverse in their nesting locations – there are plenty of shrub nesters, but there are quite a few that nest high in trees, a good number that nest in tree cavities, and a surprising number of them that nest on the ground. So much of what you’re seeing is probably an observation bias, but there may also be a bias towards shrub-nesters in areas close to human habitation – I don’t know if that’s true, but I can see how it could be.
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Probably depends on where you are, but from my perspective most of small passerines prefer bushes, large “grasses” or ground, e.g. former family group Sylviidae, but there are always exceptions e.g. tree-dwellers like Goldcrests. You can id species or genus from the nest, measurements of height, width, width of inner part, photos of inside part, layers if they are there, lateral photo will be a great help, also exact placement and height from the ground.
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So you think it is likely species specific? Hence observational bias?
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If you can find it in the library/store/online, Princeton has a field guide totally dedicated to nests, eggs and juvenile bird ID.
I believe the full title is A Guide to the Nests, Eggs, and Nestlings of North American Birds
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Each bird species has different nest site selection criteria, and some are very specific. Many passerine birds nest on the ground (and these species are most vulnerable to problems with free-roaming pets, so they disappear from urban settings). Some of those species place their earliest nest on the ground in early spring when plant cover is minimal, and as vegetation grows, their later nests are typically higher in plants and shrubs.
Some species nest dependably in thick shrub growth, or in strong herbaceous plants and small woody plants along forest edges. Edge nests are sometimes visible during nesting season by walking in the woods looking outward toward the opening. Some of these “edge” species do well in urban settings, and it’s those nests you might be seeing.
Many small passerines nest higher in trees, and some, like Golden-crowned Kinglets (in spruces), at the very tops. This is an example of a tiny bird sometimes nesting quite high.
Building a nest involves a lot of trips carrying material. When a small bird nests high in trees it is either doing a lot of work, or finding materials up high (mostly the former). I have watched Pine Warblers gather material at the ground carrying it high to a clump of needles in a Red Pine. I have also observed a Blue-gray Gnatcatcher steal materials from an Eastern Kingbird’s nest, timing its visits to coincide with times when the kingbird was off seeking material.
Many of those tree nests are still well hidden in winter. They might also fall apart sooner, being more exposed to wind and weather than one in a shrub.
I have worked on bird studies where we needed to find nests, and so when I watch birds I’m usually thinking of nesting behavior at the back of my mind.
A great book (now books) for descriptions of nest sites is the Peterson Field Guide: Bird Nests (search Peterson Field Guide: Western Bird’s Nests). I still have the original edition, that covers the whole US (and so, much of Canada). Now there are separate books for eastern and western birds. Another great reference for nest site preferences is Birds of the World (previously Birds of North America), an online resource that you can access through a library database. I no longer have access through the university here, but in a few clicks I can get to it via my local public library. More accessible, but less detailed, you can find some nest site information at the the All About Birds site. Both are hosted by Cornell University.
Some old nests are easily identifiable as a particular species’, but most are not. I have seen active nests misidentified by people looking at egg photos in books, and using nest books. For most nests I would be skeptical of ID unless the observer actually saw the bird going to or leaving the nest.
Now that you see these nests in the winter, be watchful in the coming year. If you cannot see into a shrub, then from a bird’s point of view it makes a better nest site! If you poke your head in through the outer layer of leaves, or place yourself toward the center of the shrub and look outward, you will have a better chance at spotting a nest. I have known female Indigo Buntings to nest in the same shrub, or very nearby in the year following a successful nest.
Low nesters, especially around human habitation, have very serious predation pressure. When a human goes to a nest we leave a scent trail, which for a predator like a raccoon is a meal train. Because of this it’s best to keep a distance, and never walk up to a nest and leave the same way. If you want to take a peek at an active nest, walk alongside the nest, move vegetation blocking your view with a stick, and continue on as soon as possible. If you disturb a bird at or near its nest during nest-building, egg-laying, or early incubation it will very likely desert the nest.
This might be more than you wanted. Bird nesting is sort of my “thing.” 
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No, it’s not too much! It was a very instructive guide. I often see the same species in the same areas (mostly along river banks) from year to year, and it is very interesting to read about how they nest. I would like to see more of the nesting behavior, but I don’t really know how to find them or photograph them safely. I will not leave a track for raccoons etc.!
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I found a lot of similar titles and most are out of print (some may be the same book with different covers). But I did find this… is this the one you’re talking about?
https://www.acornnaturalists.com/nests-eggs-and-nestlings-of-north-american-birds.html
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Another good book to find is:
“The Birder’s Handbook: A Field Guide to the Natural History of North American Birds”
by Paul Ehrlich, David S. Dobkin, Darryl Wheye
It has nest types, nest locations and a lot more information. It is a good reference book to have on your shelf to pick up from time to time.
Different species of smaller birds nest in different parts of a habitat. Some nest on the ground, some in the low bushes, and others in various levels of the trees. For example: the cerulean warblers nest in the tree tops. They are difficult to find. So, you have to look early in the springtime when the leaves are just growing.
Side note: I used to participate in a volunteer raptor nest survey. I used to go out in the winter to find nests. I would either take GPS readings or draw a map of the area for the next spring.
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