This past summer, I worked with three species of Terns in the Isles of Shoals in NH: Common Terns, Arctic Terns, and Roseate Terns. I have attached a video I took of my favorite species of tern: Roseate Terns. Roseate terns can be distinguished from other species of terns in a number of ways: both adults and chicks have black, rather than reddish orange, beaks; chicks have black feet and greyish-white coloring with dark spots; and both adults and chicks have a distinct, deep, raspy call. In this particular video, a Roseate chick is wandering around on a rock, and squawking. On either side of it are its two parents, which are squawking as well. They are protecting their chick from other tern parents, as well as from any other birds that are flying around. It is extremely important for at least one tern parent to attend to their chick at all times, because chicks are constantly in danger from other parents, predatory birds such as gulls, and even other (usually older) chicks. The danger that other parents pose to tern chicks is aggravated by their habit of nesting extremely close together: terns will build nests a bird's length apart! As you might imagine, this can evoke particularly violent interactions between sets of parents that are trying to protect their eggs and chicks in such a small, crowded space. In this video, with one parent on either side of the chick, it is clear that the parents are actively protecting their chick by loudly warning off intruders. The ability of parents to successfully chase away predators is vital if the chicks are to survive. In addition to merely warning predators vocally, when an intruder comes too close to the nest or even the colony as a whole, terns will dive and attack it. Whenever I entered the colony to band chicks or to do observations, I had to wear a padded hat to protect my head from the terns; their beaks are sharp enough to cause severe damage to the top of your head!
Here is some additional information about Roseate Terns:
Posted by Johanna Brophy (Group A, blog post #3)
This is so cute! This relates to the first blog I wrote about boobies and child abuse. It seems to be a popular form of looking out for your own and natural selection. Do these species of terns share signals between species just as the gulls in class did? I would imagine so. Did you ever see the Roseate Terns making this call in another context? Again, like the gulls, I wouldn't be surprised if this call had more than one meaning. Did you get to see this chick grow up and leave the nest? What exactly is the nest made of?
ReplyDeletePosted by Chelsea Van Thof.
Well it would make sense for terns to have some characteristics in common with gulls because they are in the gull family, but I think that their signals are still pretty distinct from the black-backed and herring gulls we saw in the video in class. I also think that their calls could be used in different contexts, but the only contexts that I really observed were fights over territory and food and the protection of their chicks. Most of the Roseate chicks we followed survived long enough to fledge the nest, but I'm not sure how many survived beyond the end of the summer. Roseate nests are much more intricate and hidden than either common tern or arctic tern nests; they make nests either hidden in tall grass or under/ in crevices of big boulder piles. Their nests are generally made of grass.
ReplyDeletePosted by Johanna Brophy