Wednesday, April 20, 2011

Tree Swallow

Photography makes me more in tune with bird behavior.  Perhaps, as I try for at least one photo in focus, I spend more time looking at common birds.  These Tree Swallows, photographed on 12 April 2011 near Circle Lake in Rice Co., offer an example.  I noticed the bird on the right give several yawns.  This gaping did not appear to be sexual, as other female birds do to attract males during courtship; nor did the behavior appear to be aggressive.  Robertson et al. in Birds of North America Online write that perched Tree Swallows have three types of stretching--two different sorts of wing stretches, and a "gape to stretch jaw muscles..."  Finely tuned jaw muscles must be of importance to aerial feeders like swallows. 
While I photographed, both birds performed a lot of self-maintenance.  I was excited to catch this swallow scratching.  Two types of scratching exist in birds: direct and indirect.  In direct scratching, the leg is raised under the wing.  In indirect scratching, like being shown above, the leg is lifted over the wing.  Tree Swallows use both types of scratching.  When perched, they employ indirect scratching.  Flying swallows will often scratch using the direct method (Robertson et al.). Most birds only use one type of scratching.
Since Tree Swallows can survive on seeds and berries, they winter in fairly northern climes along coastal areas of the southeast Atlantic and the Gulf coasts. Hence they are usually our first swallows to return to Minnesota in spring.  Tree Swallows breeding in bluebird houses can be a bane for the bluebird enthusiast.  Tree Swallows tend to be monogamous, in as much as males do not abandon their mates nor do they take on multiple females.  The species does enjoy extra-pair copulations.  Studies have shown about half of Tree Swallow nests contain young not fathered by the resident male (Robertson et al.).

1 comment:

  1. Randy Frederickson writes"I see it suggested often, but personally believe the amount of food tree swallows consume that are berries/seeds is extremely small. They succumb to cold, wet spring weather just as quickly as martins seem to. And a few years back, when we had a cold spring bout like this, I posted a question on MOU-net asking if ANYONE had ever seen (first hand) tree swallows eating berries or seeds and not one person had. They are starving now, someone should be seeing them eat berries, but we don't (or we don't have the appropriate berries here)."

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