Jan 14 2011

Dominance

Published by at 7:10 am under Bird Anatomy,Bird Behavior


I usually reserve Friday’s blog for an anatomy lesson but today’s topic on bird behavior does have anatomy in it.  Dominance among birds, as among humans, is expressed in both behavior and outward appearance.

If you’ve watched birds at your feeder for any length of time you know some birds are dominant over others, not only between species (blue jays rule!) but among the same species (some cardinals are bossier than others).

The dominant birds tend to be physically larger than their subordinates and sometimes they’re marked differently.  This is especially true of male house sparrows who wear their status on their chests. 

Among researchers, the bib on a house sparrow is called a “badge of status” because it’s a clear outward sign of dominance.  All house sparrow bibs become fainter in winter but at any given time of year the bigger and darker the bib, the more dominant the bird.  In a contest between the two birds pictured above, the one on the left wouldn’t even attempt to challenge the one on the right.  Mr. Big Bib wins, just by showing his chest.

Because they’re unevenly matched, these two are unlikely to fight at all.  However, males with similar badge size fight more often between themselves perhaps because it’s not obvious who’s in charge.  Eventually the contests work themselves out and everyone knows his place.

Jays can avoid contests altogether by figuring out the hierarchy from afar.  Here’s a hypothetical story showing how they do it:

Two jays, Charlie and Bob, are in the same flock where Charlie knows he’s subordinate to Bob.  One day Arnold shows up.  From a distance Charlie can see that Bob is subordinate to Arnold so Charlie knows, even before he meets Arnold, that Arnold is dominant over him.  This saves a lot of trouble in the long run!

It sounds almost human.  ;)

(photos from Wikimedia Commons)

One response so far

One Response to “Dominance”

  1. kellyon 14 Jan 2011 at 10:56 am

    funny. i have been thinking about house sparrows recently. i am going to bike the katy trail in missouri this spring and realized that the eurasian tree sparrow was the bird to look for in st. louis. i began to wonder why the transplanted house sparrow did so well readily expanding its range while the eurasian tree sparrow only established itself locally. my thoughts turned to the relatively aggressive nature of the house sparrow as a species. i guessed that the eurasian tree sparrow was less so. found this informative entry online:

    http://mdc.mo.gov/conmag/2003/05/eurasian-tree-sparrow

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