Nests are energetically expensive to build, and yet oddly disposable. Not only do birds only use their nests for rearing young, but the nests are also entirely disposable and only used for one breeding season! As with all things biological, there are of course exceptions: Phoebes, geese, osprey, and other birds, will nest in the same spot year after year. While the platforms may be the same from year to year, the birds often build an entirely new nest on top of those from previous years. One absurdly overgrown nest constructed by a pair of bald eagles weighed in at over 4,000 pounds (it even has a page in the Guinness Book of World Records – source). Other birds – like barred and great horned owls – are lazy and just use old abandoned nests built in previous years, those these are nests built by other species.

Phoebe nest in eaves of Orchard Cove house
Female mourning dove on nest (Green Mount Cemetery, Burlington)

Building a nest

Building a nest can be tough work. Depending on the species, construction can take a couple of minutes or a couple of weeks. They can be built by the female alone (e.g. robins) or as a joint venture between males and females (check out this video of a pair of mourning doves constructing a nest).

Nest built on the ground are usually a much simpler engineering feat. A killdeer constructs her nest by simply scraping away a shallow depression in sand and lining it with small rocks or dried grass. Again, exceptions. Ovenbirds build elaborate “ovens” on the ground that can take up to a week to construct. Cavity nesters like nuthatches and chickadees save energy by refurbishing old woodpecker holes or branch scars and just lining the inside with soft materials. Or if you’re a brood parasite, like the brown-headed cowbird, you just forego nest building altogether and lay your eggs in another bird’s nest. Also saves you the hassle of rearing your own young.

White-breasted nuthatch investigating a cavity in a sugar maple, possible nest site (Ethan Allen Park, Burlington)
A house wren with pine needles for its nest cavity (Backyard, Burlington)
Time for housekeeping

Construction of the nests is one thing, but the nests can get real dirty real quick once those eggs hatch, and so birds must be ever-vigilant to keep the nest clean. Baby birds help keep the nest clean by producing fecal sacs, a mucous coated feces common in birds with altricial young. Grackles nest near water and will either eat the fecal sacks (those mucous-covered fecal sacs produced by young birds are rich in nutrients) or carry them off to discard away from the nest. interestingly, the older nestlings get, the more developed their digestive tracts become, and the less nutritious the fecal sacs are. Parents are more likely to ingest fecal sacks of younger nestlings.

Osprey on a constructed nest platform (Shelburne, VT)

Construction of the nests is one thing, but the nests can get real dirty real quick once those eggs hatch, and so birds must be ever-vigilant to keep the nest clean. Baby birds help keep the nest clean by producing fecal sacs, a mucous coated feces common in birds with altricial young. Grackles nest near water and will either eat the fecal sacks (those mucous-covered fecal sacs produced by young birds are rich in nutrients) or carry them off to discard away from the nest. interestingly, the older nestlings get, the more developed their digestive tracts become, and the less nutritious the fecal sacs are. Parents are more likely to ingest fecal sacks of younger nestlings.

Energy savings – rookeries

Building a nest is tiring work. And defending the nest can also be tiring work (both take away time that could be spent foraging). There are two obvious workarounds. Birds like great blue herons (and other herons and egrets) congregate together during the nest season to build nests and rear young. There are plenty of other perfectly serviceable habitats for nest building, but nesting in these rookeries increases the number of individuals to defend an area from predators and also reduces the likelihood of being the one a predator eats.

A pair of great blue herons at the rookery. Below, a green iguana covered in heron droppings - possibly
A green iguana covered in great blue heron droppings
Energy savings – compound nests

Sometimes communal nesters get carried away and their nests blend at their borders and weave into their neighbors nests. Monk parakeets, an invasive species in many North American cities, build compound nests that contain 20 to 200 active nest cavities. Unlike most nests, these monstrous creations serve the parakeet colonies year round.

A collective nest built by multiple pairs of monk parakeets (from Wikimedia)

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