A Googling friend supplied me with some possible answers to my questions about the surfeit of agitated robins in my woods (see previous post). The theories are interesting.
(1) Robins are territorial loners in the spring when they are breeding, but they stick together in large flocks in the wintertime. As winter wears on they simply get on each other's nerves.
(2) Robins practice "thermo-regulation," roosting close to each other to take advantage of each other's body heat. The colder the day the closer they convene. Familiarity breeds contempt even in the robin world.
(3) Robins share information during their roosts. For instance, a skinny robin will roost next to a fat robin and then follow it the next day when it forages. A skinny robin has to be sure the fat robin's name is not Bernie Madoff.
It appears robins are more like humans than we probably care to admit.
Many thanks to my robin researcher.
BLOG NOTE: Deerfield Diary will be on a brief vacation until Tuesday, January 20. Robins aren't the only ones who need a little break.