Birds in the city.

[Coldjensens]

Originally Posted by Parnassia

Its winter. Many bird species gather in flocks in the non-breeding season. Once breeding season starts in spring they tend to separate into pairs in preparation for nesting and rearing chicks. That's the time of year when they get territorial (which is the main reason they have more elaborate calls (songs) at that time of year...to announce/defend their territory and display their good genes to females) and then defend nest sites. Yes, swallows and many other birds dive bomb intruders that get too close to nests. When nesting season is over, their territoriality tends to break down and all those pairs and those successful pairs with chicks of the year start gathering in flocks again. These birds are not defending nests or territories so they aren't dive bombing intruders.

The time of day also plays into it. Many flocking birds gather into communal roosts at night especially in non-breeding season. More eyes and ears to detect threats. Communal roosts can be used night after night for months. What may be attracting them to the area at night is lack of threats/predators. Its possible they shifted to that area recently because something disrupted a traditional roost site somewhere else. Industrial facilities (think factories, electric utilities, orchards, mills, feedlots, bulk grain storage and other commercial agriculture sites) can haze communal roosts to force them to move. Communal night roosts can be so huge they cause structural damage to large trees and even some buildings. You can imagine the cleaning.

Starlings, cowbirds, blackbirds, crows, gulls, ducks, geese, swans, herons, vultures, bald eagles just to name a few species that roost communally at night. About the calls you are hearing. Those are not territorial "songs", they are simpler social calls to other members of the flock. I wouldn't say English sparrows are "loud and raucous", neither are pigeons (aka rock doves which is what "city pigeons" are). Certainly not swallows. They feed on flying insects. They tend to migrate a lot farther south for winter. Not too many flying insects available during Michigan winters especially in the city.

Thanks. This is interesting. One thing that occurs to me is in Canada they have greenhouses for pot that light up the night sky. When there are clouds for it to reflect off of, it looks like sunset only in the east from 30 - 50 miles away. Maybe the birds moved away from that. That is the biggest environmental change I can thing of recently in this area.