On a beautiful sunny day last week I decided it was time to check on bluebird nest boxes. I had seen several Western Bluebirds (Sialia mexicana) scouting for possible nesting sites and it is that time of year to make sure the boxes are in good shape, clean and ready to go. But what I saw rather shocked me. Click on photos for full sized images.
There were groups of Western Bluebirds aggressively chasing each other. It seemed that males were chasing males and females chasing females. In all these years of monitoring bluebird boxes, I had never seen this behavior.
According to Birds of North America Online “physical interactions include fights, pecks, supplanting attacks or flybys, chases, and collisions. In conspecific fights, individuals contact each other with beaks, feet, and wings.
During fights, the birds face each other, grappling with their feet, and sometimes falling to the ground. Head-pecking also occurs during fights, which appears to be highly motivated. Often fights are extended, with combatants falling to the ground, paying no attention to their surroundings.
Males are aggressive to males; females to females. Both adults can be aggressive to juveniles of either sex. Instances of male-to-female and female-to-male aggression also occur, but are rarer than intrasexual aggression.
While chasing intruders, males may grab opponents’ legs causing both combatants to fall to ground. Once on the ground, the aggressor may pin the opponent on his back by standing on him, then spreading his wings wide over the opponent; from this position, the aggressor may strike at the opponent vigorously with his bill.”
After watching this encounter, it seems that the females exhibit the same aggressive behavior.
Once the fight had concluded, the female victor flew up onto the nearby nest box along with a male.
The pair then proceeded to investigate the birdhouse…
From the outside in.
Apparently satisfied with her mate but not sure of this home, the female flew off to view another model in the same neighborhood.
The male watched her closely, then followed in pursuit.
Larry Jordan was introduced to birding after moving to northern California where he was overwhelmed by the local wildlife, forcing him to buy his first field guide just to be able to identify all the species visiting his yard. Building birdhouses and putting up feeders brought the avian fauna even closer and he was hooked. Larry wanted to share his passion for birds and conservation and hatched The Birder's Report in September of 2007. His recent focus is on bringing the Western Burrowing Owl back to life in California where he also monitors several bluebird trails. He is a BirdLife Species Champion and contributes to several other conservation efforts, being the webmaster for Wintu Audubon Society and the habitat manager for the Burrowing Owl Conservation Network. He is now co-founder of a movement to create a new revenue stream for our National Wildlife Refuges with a Wildlife Conservation Stamp.
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