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Center for

Environment & Society

Life Histories

Life history is the series of changes undergone by an organism during its lifetime.


  • There are many different types of nests made from hundreds of different types of naturally-occurring materials as well as human-made objects. Many small songbirds make small woven cup nests made up of grass fibers of differing thicknesses and lengths, small sticks, lichen, spider webs. Nests are often lined with small delicate grass or root fibers, or some birds like Tree Swallows use feathers the find to line their nest. Several bird species utilize man-made structures to build their nests on or within. Eastern Bluebirds, Tree Swallows, Carolina chickadees and Tufted Titmouse all are common birds that can be found using man-made nest boxes. Chimney Swifts nest in unused chimneys, Osprey with readily nest on towers, buildings, signs across highways and of course man-made platforms specifically made for them.
  • Most songbirds do not use the same nest more than once, even within a season when they nest multiple times. Exceptions to that rule include Barn Swallows, Eastern Phoebes and cavity nesting species like woodpeckers and Eastern Bluebirds and Tree Swallows. Raptors will use the same nest from one year to the next, Bald Eagles will use the same nest for many years in a row and continue to add sticks each year to fix any damage that may have happened during the winter, but it is also part of the annual courtship and pair bonding that takes place prior to the nesting season.  
  • There are some bird species that don’t make nests and just lay their eggs in a shallow scrape in the ground. Most shorebirds do this and a good example of this is the Killdeer. Killdeer just make a small scrape in the gravel, sometimes they add a few smaller pebbles to the nest edge and then lay their eggs. They rely on the camouflage of the eggs that blend in with the gravel for protection.  
  • Most species of birds nest in an area that is defended and/or protected just by that pair of birds, that is the female places the nest somewhere in or near the males territory. The nest is hidden extremely well and they rely on camouflage of the nest and the cryptic coloration of the eggs to blend in with the surrounding vegetation to avoid nest predators. Colonial nesting species don’t hide their nests and rely on the safety in numbers strategy to defend their nests. All members of a colony, even in a mixed species colony, will work together to drive a would-be predator away. Colonies of nesting birds are often located on islands in the ocean or large rivers to further help with predator protection. Colonial nesting birds don’t always choose islands to nest on, take for example the Least Tern that nests here in Maryland. Our rivers no longer have suitable habitat for them to nest on and now they have taken to nesting on gravel roofed buildings that are located within a few miles of the rivers (like at the Chestertown Acme). These rooftop islands work pretty well at keep most nest predators at bay, though the birds still have to defend their nests from avian predators such as crows and Great Horned Owls.
  • Egg color and patterns vary among species.  Each egg is subtlety unique. 
  • Females of just about every species of bird develop brood patches just before they start to incubate the eggs. A brood patch is the area of a bird’s belly where the feathers are dropped so that the bird can transfer the maximum amount of heat to the eggs through its skin. Males of some species also develop a brood patch, but they are never as extensive as the females. 
  • Chicks can hatch synchronously or asynchronously.  Songbirds don’t start to incubate the eggs until the clutch is complete, this way all the chicks will hatch on the same day (synchronous). Birds of prey, Pelicans, and Egrets start to incubate after the first egg is laid so the chicks hatch over a period of several days (asynchronous). This strategy allows for the maximum number of offspring taking into account that food availability is unknown at the time the egg is laid.

Site and Mate Fidelity

  • Most birds are highly faithful to the same breeding territory and the same wintering territory each year. Songbirds, such as Grasshopper Sparrows and Field Sparrows, return each year to the breeding grounds and the males establish and defend the same territory as they did the previous year. By coming back to an area you are already familiar with gives the birds a huge advantage over new individuals in the breeding population, these birds have knowledge of the predator community, where productive food resources may be located and also may know their territory neighbors from previous years. 
  • Many long lived birds stay with the same mate for life, great examples of this are Bald Eagles, Swan species and Albatross species. Songbirds also show mate fidelity within and between breeding seasons. Not are songbirds will stay together from one nesting attempt to the next, divorce most often occurs after an unsuccessful nesting attempt. Of course birds will make new partnerships if a mate dies.