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.
Oh to be a bluebird in love!
httpv://youtu.be/iEQujM3fF7Q
References:1Birds of North America Online
Fascinating photos! One of my college professors was involved in a study on (Eastern?) bluebird aggression some years ago. They started by securing carstruck bluebirds in others’ territories, and he had some great (and kind of unsettling) stories of the resident bluebird’s attacks. I believe they even went so far as to try blue bouncy balls on fences, with similar violent effects!
Wow, this is a serious fight. I don’t think I’ve ever seen wild bird fighting for so long! They were at the mercy of any predator, be it terrestrial or aerial for so long.
Joel I was amazed I had not seen this behavior before but it appears to be very common. The information on Birds of North America Online also mentioned studies by Gowaty and Wagner on Eastern Bluebirds with “models” (inanimate objects) which showed the same aggression.
You are correct Alfredo. The video in this post is not mine and the females I watched didn’t fight that long but they were totally oblivious to my presence and therefore vulnerable to predation just like the males in this video.
Nice post Larry!
The fight between the two male bluebirds I witnessed went on for over 45 minutes, fighting on the ground, then up in the trees, then mid-air swooping from tree to the ground, then back to the ground again. It was their rustling in the leaves that caught my attention, and it was fascinating to watch! I noticed one lone female watching from a tree above. Thanks so much for sharing the video. Sorry it wasn’t better quality.