Less usually more for ground nests Eggs’ camouflage patterns make it harder for predators to spot them

Last week I attended a delightful slide show at the Fields Pond Audubon Center in Holden. It was the perfect primer for the coming spring: bird nest construction and identification.

The presentation was given by Jerry Longcore, University of Maine faculty associate in Wildlife Ecology and leader of the USGS Patuxent Wildlife Research Center. Longcore has amassed a large amount of avian research over the years, spending long hours in the field finding, photographing, and identifying nests of many bird species. His professionalism in no way dimmed his admiration and awe for his subjects, and he enthusiastically shared his experiences with us.

Longcore began his presentation with examples of nests made by ground-nesting birds. Most often, such nests are open in construction – meaning they are not funnel-shaped or enclosed in any way – so eggs in these nests are very cryptic in coloration.

Speckled and patterned in such a way, they blend so well into the surrounding vegetation a predator may not see them, even up close.

Ground-nesting birds such as the killdeer are famous for hiding their nests right out in the open. They really don’t use any nesting material at all, depositing their eggs in a slight depression with scant material raked in around them. Longcore mentioned the killdeer’s well-known distraction display, that of fluttering along the ground while dangling a wing as though broken. This tactic is designed to draw a predator (or curious birdwatcher) away from the vulnerable nest; once you see such a display, he said, stop and look carefully at the ground around you – often the nest will be almost at your feet.

Another ground nester, the ovenbird, constructs a dome-shaped nest resembling an oven, so giving the bird its name. It is made of dead leaves, plant stems, and fibrous bark. Interestingly, the inside is lined with deer or horse hair. In this case, it is the entire nest that is camouflaged, rather than the eggs being cryptically colored, to avoid or reduce predation.

A third example Longcore gave of a ground nest is that of the blue-winged teal. A small dabbling duck, the teal nests in the completely open habitat of marshland vegetation. Its nest is open, with light-colored eggs lacking in cryptic coloration.

However, when the female leaves her nest, she carefully covers the eggs with down feathers plucked from her body, effectively hiding them from view.

Longcore presented the nests of many more birds, too numerous to go into detail here: bank nesters, such as the bank swallow and belted kingfisher; birds that use mud and saliva to mold their nests, such as the barn swallow, eastern phoebe, and cliff swallow; and cavity nesters, such as the bluebird and tree swallow. In regard to the tree swallow, Longcore mentioned the use of feathers in the nest seems to be crucial and is an indicator of when eggs will appear – usually within one to two days of feathers being placed in the nest.

Some birds, such as raptors, place fresh greenery in the nest once it is complete. This is what the eagles on the Biodiversity Research Institute “eagle cam” (refer to last week’s column or visit http://briloon.org/ed/eagle/), have done with a sprig of white pine. This is thought to combat parasites such as feather mites. Other greenery may be placed in the nest for moisture, Longcore said.

Join Jerry Longcore for the field portion of his bird nests and construction presentation, on March 18 at 2 p.m. Participants will look for and learn how to identify bird nests. There is a small fee. For more information and to sign up, call the Fields Pond Audubon Center at 989-2591.

Also coming up: “King Eider Chase to Southern Maine,” this Sunday; and “Owls in the Night,” on Tuesday. Call the Audubon Center for more information and to sign up.

NEWS bird columnist Chris Corio can be reached at bdnsports@bangordailynews.net