Tuesday, February 16, 2010

Ring-billed Gull behavior

Birding can be many things to many people. For some, nothing beats chasing a rarity in their home state. For others, the passion is holding a bird in the hand and studying molt limits. Or it can be witnessing the spectacle of massive bird migration, just being engulfed by huge numbers of birds on the move.

I enjoy all these things, but for me, I think what I like best about birding is observing bird behavior. I like holding a Wilson's Warbler in my hands, blowing its belly to determine body molt and breeding status, or stretching out a wing to look for feather wear, but in the end I find it more interesting to observe that Wilson's Warbler in the wild.

Today I have a sequence showing part of the behavioral repertoire of Ring-billed Gulls. The previous post, also about Ring-billed Gulls, was mostly about plumage. Now I want to focus on behavior.

Today I went back to the same spot where I photographed Ring-billed Gulls a few days ago. This time I brought some bread myself. It didn't take long for the gulls to realize what I was up to, and they posed very obligingly for a morsel of bread. The photos are a bit dark, because it was snowing at the time.

Take a look at the two left birds in the top picture, both adult birds in basic plumage. The bird on the left is out of focus on this first picture, but we can still see the red eye ring and red gape of the mouth, good marks for an adult (3+ years) bird. The next bird - focused - also shows these marks. The time of this photo is 9:51:26 AM, i.e. 51 minutes and 26 seconds after 9 AM.

9:51:28 AM. The left bird has started to move a little closer to its neighbor, which, judging from the way it has retracted the neck and raised the bill, seems to be threatened by that behavior.

9:51:31 AM. Both birds are now engaged in calling, with lowered head posture. The left bird is a bit smudgier on the head than the right, but both have yellow eyes and red eye rings and gapes. In this posture, the head is lowered but the neck is raised. The other birds on the railing seem relatively undisturbed.

9:51:33 AM. Both birds now engaged in a head-toss, while still calling. The BNA account for Ring-billed Gull mentions a study by Southern & Southern (1982) of aggressive behaviors in this species. According to them, the Head-toss is "a single extreme backward toss of the head, given before call terminates."

9:51:36 AM. Both birds still calling, but each bird stretching its neck in opposite direction, possibly to see the other bird better. My impression of their body language is that the light-headed bird appears to be dominant over the dusky-headed bird, but it's hard to know for sure what's going on inside their heads... Note how the birds behind these two are alertly observing this, and that a third bird is also calling.

9:51:39 AM. Our two protagonists are still calling, and the light-headed bird still seems to have the upper hand.

9:51:42 AM. The light-headed bird appears to have established dominance over its neighbor, and seems ready to terminate the aggressive behavior. (Observe also how the unfocused bird in the foreground has barely changed posture during the last five frames, i.e. for 11 seconds. It's just looking down.)

9:51:45 AM. Uh-oh - excitement! One of the birds in the back is taking off, while our dominant bird, still excited, resumes calling. The dusky-headed bird now strikes a very submissive pose, acknowledging the dominance of the light-headed bird.

9:51:55 AM. This is what all the excitement was about: a first-cycle bird landing on the railing and chasing off adults! Generally I would expect older birds to be dominant over younger ones, but this young bird, full of chutzpah, is not afraid to charge his way to what it thinks must be the best seat in the house. It shamelessly landed on a spot where an adult was standing earlier - the bird taking off in the previous photo.

9:51:59 AM. The young bird is moving closer. How will the light-headed adult, with the victory over the dusky-headed adult still fresh in its mind, react to this sudden act of juvenile aggression?

9:52:03 AM. The first-cycle bird is still charging forward. It wants to be as close to the photographer as possible, because it has observed that the photographer has bread in his pockets. Note the feet of a bird in the air in the top right corner: that bird was standing next to the first-cycle bird in the previous photo.

9:52:06 AM. I think - but I am not sure - that the young bird is now chasing away our earlier duo. Both seem pretty much resigned to indulging the younger bird's aggression. They've already seen it chase away three other adults, and figure they are next.

9:52:09 AM. Having cleared the entire railing of conspecifics, this bird is ready for some bread.

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