Minneapolis-St. Paul Star Tribune – Jul 12 12:14 PM
Q In early July, I noticed that house sparrows had moved into the nests of the cliff swallows on the west side of our building at work. Swallows occupied most of the nests through June, but after July 4, sparrows resided in most of them. Did the sparrows evict the swallows, or did the swallows have time to fledge their young, then abandon the nests?
By The Minnesota Ornithologists Union
Last update: July 12, 2014 – 1:38 PM
Q In early July, I noticed that house sparrows had moved into the nests of the cliff swallows on the west side of our building at work. Swallows occupied most of the nests through June, but after July 4, sparrows resided in most of them. Did the sparrows evict the swallows, or did the swallows have time to fledge their young, then abandon the nests?
A Because of the timing, it is difficult to say whether the nests were abandoned before the house sparrows moved in or the sparrows took over the nests.
Cliff swallows are a protected native species that begin breeding in May and breed into July. They have one or two broods.
House sparrows will use the nests of both cliff swallows and barn swallows. Sometimes house sparrows fight for the nests and kill the young cliff or barn swallows. Sometimes they move in after the young have fledged.
However, recent research suggests that house sparrows do significant damage to barn swallow nesting colonies. In Maryland, sparrows reduced the fledging success rate of one barn swallow colony by 45 percent.
Why birds form a mob
Q I’ve seen groups of crows or blackbirds dive-bomb a hawk. Why do they do that?
A The behavior, called mobbing, is very common among crows.
Crows mob hawks and owls because they perceive these birds to be a threat. And it’s true that hawks have been known to kill crows — sometimes even when being mobbed — by flipping over to strike out at an attacking crow with their powerful feet and talons. That’s why crows are careful to stay above and behind a hawk when mobbing.
Other birds that frequently chase or mob hawks are Eastern kingbirds, blue jays and red-winged blackbirds. Like crows, jays usually mob a hawk or owl with many loud attackers, while single kingbirds and blackbirds typically give chase one bird at a time. Even some small birds, such as chickadees and nuthatches, will mob owls to protect themselves and their young.
This column is prepared by Minnesota Ornithologists’ Union (MOU) members Mark Alt and Anthony Hertzel. To ask questions for this column, call 612-673-4363 and leave a brief message. Or e-mail birds@stribmail.com. Questions will be answered in the newspaper only. For information about the MOU write to: Minnesota Ornithologists’ Union, Bell Museum, 10 SE. Church St., Minneapolis, MN 55455.
