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The Variety of Bird Nest Design

   Birds whose very survival depends largely on their ability to move rapidly away from danger by flying, have a huge problem in nest design.  Namely that nests are stationary and are subject to predation if the nest is found.  Thus it is very interesting to observe birds during the nesting season to observe how they change their behaviors.  For example the male will sing loudly and for prolonged periods while he is recruiting a mate, defending his territory, and the female is making the nest.  But once the eggs are laid the parents generally do not sing much and are very secretive in going to and from the nest.  This change in song is so distinctive that when you hear males singing later in the breeding season you may assume that they probably are in the "lonely hearts club" and have failed to find a mate.

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Nests are extremely variable in design and placement and this tends to be a rigid part of the bird's behavior.  Cavity nesters such as martins and bluebirds will quickly adopt a nest box since it is simply an artificial cavity, but they will not nest in an open bush.  This can become a problem since cavities are in short supply and are now being taken over by aggressive exotics such as starlings.  This stereotypical aspect of bird behavior is hard for us to comprehend since our human behavior is much more flexible.  But birds are creatures of their evolutionary history and much of what they do is instinctive and pre-programmed.   But with the rapid change in habitats due to human manipulation of the planet, those species with the greatest chance of survival are showing some ability to adapt.  For example the great egret in Florida is able to feed now in a variety of habitats such as yards on terrestrial prey such as the abundant introduced brown anole and it is thriving.  Similarly the red bellied woodpecker is moving north and is even eating fruit in orchards and yards.  In contrast the scrub jay in Florida is almost surely doomed since it is almost entirely limited to rare scrub habitat which is disappearing.  

 

So consider the variation in nests among a small sample of birds that I have encountered recently.  I highly recommend a book entitled "A Guide to the Nests, Eggs and Nestlings of North American BIrds" by Baicich and Harrison as a source of information.  The two ground nesting birds I have come across were the grouse and the killdeer.  Neither really makes a nest in the traditional sense but places the eggs in a scrape in the woods for the grouse, and in an open field for the killdeer.  They must remain well camouflaged while incubating and then the precocial young leave the nest immediately and follow the parent(s).  The young cannot fly for some time but are able to run and hide from predators.

 

In total contrast, most birds in our yards lay eggs in carefully constructed nests and the young are born blind and naked and require some time to develop in the nest (altricial).  But the nests can be difficult to find.  For example redwings are one of the most common birds and make a nest of grasses in marshes or in uplands with dense grasses or weeds.  The nest is woven around the stems of the grasses, and is defended by both parents.  Robins on the other hand make a nest of mud and grasses in shrubs or trees.  The mourning dove makes a minimal nest of sticks and grass.  The tree swallow nests in cavities such as nest boxes and makes a nest of grasses and feathers.  An  extreme type of tree nest is made by the Baltimore oriole that weaves an amazing nest of grasses at the tips of tree branches; this seems to be a special adaptation against predation by snakes.  A similar type of predator defense is found in the cliff swallow that makes a nest entirely of pellets of mud attached to the undersides of rock ledges or bridges.

 

I think you will find it both fun and informative to learn more about the nests and eggs of our local birds.  It is challenging to find the nests of some species.  In fact there are many common species around our house for which I have never found the nests, which shows how secretive they are in protecting their young. 

 

Bill Dunson 
wdunson@comcast.net 

http://www.galaxgazette.com/blogs 

http://lemonbayconservancy.org/dunson_archives.htm