It's spring — bird nests and nesting

This past weekend many children participated in a traditional spring ritual — receiving baskets lined with green artificial grass and gathering “eggs” of various sorts to fill those baskets.

Engaging with this symbolism of renewal and rebirth helps us all identify with the dominant spring activities of our avian neighbors, nesting and laying eggs.   

Bird nests attract our interest because they often are visible, sometimes into the fall long after breeding season, when trees lose their leaves and expose them.  

Worldwide there are more than 10,000 bird species and the vast majority build species-specific, unique nests. A quick count of our local breeding birds indicates to some 110 different species (over 1% of the world’s total) nest here in Thurston County.  

My initial assignment for this week’s column was to write about all the different bird nests one might find in our county. However, after a quick review of a field guide to bird nests, I realized this could be almost a book-length assignment. So, I am offering a mere summary.  

Field Guide to Western Birds' Nests

Photo by George Walter

A portion of our local birds nest in cavities, either natural or created. The woodpeckers create their own and many other birds (chickadees, some swallows, many owls, for example) borrow them in future years. However, these are not the visible nests that attract our attention.  

A few of our bird species nest in colonies because having neighbors provides protection from predators. Great blue heron colonies, called rookeries, are also communal, and there’s one on Capitol Way in downtown Olympia near the Farmer’s Market.

Purple Martins - at NRNC

Photo by George Walter

Cormorants also nest in colonies, and they have a prominent nesting site at the Woodard Bay Natural Resources Conservation Area. Purple martins each nest in a separate cavity but tolerate close neighbors in a semi-colonial situation. You can see martins nesting close-up at the Nisqually Reach Nature Center at Luhr Beach. 

Almost all our county’s breeding sparrows create woven grass nests on or near the ground. This may seem risky, but it is highly successful. The grass provides good camouflage and, when brooding eggs, the brownish female remains very still. If you are walking in a grassy place in spring and suddenly a sparrow jumps up and flies away, it a very likely there is a nest there.  

Ornithologists have researched nest building and concluded it’s largely instinct driven — that is, genetics drives a bird to construct a species-specific type of nest. But individual birds sometimes customize their nests based on experience and observation. Still, when we find a nest, we can usually identify what bird species constructed it. We just have to wonder whether it has some subtle custom features that increased its chance of success. 

Then there’s the yellow warbler. This migrant is arriving about now, in late April. The male is singing, establishing a territory and attracting a female. She will almost immediately start nest building. Her preference is a vertical fork in a large shrub or small tree (for example, a willow or hawthorn), 10 to 40 feet above the ground, often near water. First, she builds a 3-inch cup-shape of grass, bark strips and the like, and then “decorates” it with lichen or other bits and pieces. She then lines the inner nest with whatever fine fibers and fluff might be available. 

Disguising and/or hiding the nest is important to discourage nest predators — readily visible eggs offer an easy meal for crows and jays. Once completed, the warbler lays her eggs, one each day, and otherwise stays away from the nest. This limits the risk of predators following her before she starts to brood her eggs. After 14 or so days of brooding, the eggs hatch all at once, and then the work really begins, as implied by Liam’s photo of the warbler young demanding to be fed. 

Brown-headed Cowbird - female

Photo by Liam Hutcheson

Brown-headed cowbird male

Deposit Photos | steve_byland

One warbler nest predator, brown-headed cowbirds, are an exception to the avian nest-building imperative — they don’t build nests at all. The reproduction strategy of this nest predator is to look for another bird to raise her offspring. The female cowbird lays her eggs, often only one or two, in the nest of another species, for example our yellow warbler. If the ruse works, the foster parents will raise the youngster, sometimes at the expense of its own young.  

Cowbirds, a common summer bird, often are missed among all our other medium-sized brown and black birds. I usually notice them by the male’s unique vocalization, a short thin whistle. Males are black with a distinctive dark brown head; females are a plain light brown. They are somewhat smaller than other black birds and have a blunt, conical bill.  

Of all nests, the largest by far are those of the eagles, hawks, ospreys, herons and ravens. These are built primarily of sticks; they are large and bulky and are often used year after year. Sometimes the nest becomes so large that the tree itself collapses under its weight.  

Bald eagles build huge stick nests in locations that that become their home territory. They are usually (but not always) in an open area. I’m uncertain how many active bald eagle nests there are in Thurston County; there likely are 30 or more. That’s quite a change from 40 years ago. Before they were listed as endangered and protective regulations were put in place, bald eagles were seldom seen in our county and breeding sites were rare.  

In California, there is an active webcam that allows you to check out a bald eagle nest and its young eaglets. I have been following the site for several weeks now and thought you also might be interested. If you watch long enough you will see an adult bringing in fish and tearing them into bite-sized pieces for the eaglets.  

Bald eagle females lay eggs several days apart, but they start brooding eggs immediately. This means that the first to hatch has a maturity and size advantage over its nest mates. This California nest originally had three young, but only two have survived. Look at how the youngsters’ feathers are coming in. Even now, one of the young looks more mature although it seems likely that both will fledge.  

I am sure we all wish them long and successful lives. 

George Walter is environmental program manager at the Nisqually Indian Tribe’s natural resources department; he also has a 45+ year interest in bird watching. He may be reached at george@theJOLTnews.com 

Photos for this column are provided by Liam Hutcheson, a 17-year-old Olympia area birder and avid photographer.