I spent this past summer living on White Island in the Isles of Shoals off the coast of NH. I was an intern working for the Tern Restoration Project, which aims to restore terns back to their historical habitat.
The island we lived on, White Island, doesn't have many nesting birds on it, but connected to it at low tide is Seavey Island, which supports the majority of our tern populations.
The three species of Terns living on Seavey island are Common Terns, Roseate Terns, and Arctic Terns. The Common Terns were by far the most numerous, with a nesting population of 2000+ pairs; followed by about 40 pairs of nesting Roseates and 4 pairs of nesting Arctics. Typically, each nest will have 3 eggs, most of which will hatch. Needless to say, the island, which is very small, is also very crowded, and life is extremely difficult for these birds and their young. Not only do the tern eggs/young chicks have many predators they must survive, they must also survive the battle for food/nest space/warmth and attention from their parents. Very often, tern chicks will be attacked and killed by the adult birds from a neighboring nest, by other chicks, or even by their own parents. Also, whichever chick gets to the fish first will get fed the most, and have the best chance of survival. This is key: many, many chicks die from starvation because their parents are only able to catch enough fish to feed one or two out of the three.
Attached is a video I took from an observation blind of two Common Tern chicks. They are probably a week or so old, and they are begging their parent for food. They do this by running up to one of their parents (which is standing on the ground near them) with their beaks open. Also, they are constantly on the watch for their second parent, who is out catching fish. Whenever they catch sight of an adult who they think is their parent returning with a fish, they scramble in the direction of that bird and start begging for food.
Most likely, only one of these two chicks survived long enough to fledge the nest.
See below for the video.
Also, this is a picture of the two islands: the island on the left with the lighthouse and the house is White Island, and the island to the right is Seavey island.
Posted By Johanna Brophy (group A, blog post 2, week 4)
Why is it that only one of these two chicks will survive long enough to fledge the nest? Is it because the one with the larger beak or the one with more insistent begging will be fed while the other one will not? This hypothesis reminds me of the brood parasites that were mentioned in class, where the parasite with the mouth much larger than the other birds will fledge while the rest of the birds in the nest die.
ReplyDeletePosted by Michael Shi
Hi Johanna,
ReplyDeleteWhen you mentioned about how some adult Terns even kill thier own chicks, it made me think, do you know if they eat their chicks after they kill them or feed it to their other children. In "Signals for Survival", the movie we watched in class, we saw that gulls would kill other gulls' chicks so they can feed them to their own chicks. But in infanticide, where the parents kill their young, some researchers say that there are other motives. For example, one reason langur monkeys perform infanticide could be for population regulation or to increase reproductive success.
This was something interesting that I thought I would just put out there.
Posted by Whitney Huynh
Going off of what Whitney said, the occurrence of infanticide may in fact be a way of controlling the population, especially where the island is getting to small to support the amount of birds nesting there. If resources and territory are scarce, I wonder whether these populations will disperse to new homes in the coming years. Is the lack of food supply due to overfishing by the population, or are the fish population naturally low? It puzzles me why these birds don't try to find new nesting grounds when chick mortality is so high...
ReplyDeletePosted by Chelsea Van Thof
Wow, very cool summer. Will you be continuing with this project next year? I hope the restoration is going well. By the sounds of it, it would seem the populations are growing well, what with the amount of competition causing such high mortalities. It must be hard to see so many chick deaths. Is your group forbidden from helping the chicks? Perhaps you could try moving some of the population to a new island.
ReplyDeletePosted by Austin Gray
This article raises a question that I had thought of after watching "signals for survival". Why is it that these birds meet, mate and raise their family all on the same island? what is the benefit of this? Why not treat the island like a bar and meet your mate then leave to raise a family elsewhere with less competition?
ReplyDeletePosted by Michael Thomas
I really like that you have your own videos that you shot yourself. It makes you posts original and interesting to read. Did you take these videos as part of your internship or just for fun?
ReplyDeletePosted by Janelle Hayes
This island seems like a place where natural selection is hard at work. With that many birds crammed into such a small area, there must be huge competition for food and terretory. The fact that only 4 pairs of Arctics could continue to survive and procreate when surrounded by over 500 times their numbers in other species is quite impressive on their end. I wonder why the parents would ever attack their own chicks in an environment that is already so hostile? Maybe they are just trying to give their remaining chicks a better chance at survival; the survivor(s) would get much more food and probably be much healthier.
ReplyDeleteRhys Ursuliak
Hey everyone I'll try and answer most of the recurring questions. The reason I said that most likely only one of the two chicks will survive long enough to fledge the nest is that on average, each nest produces around 1.5 chicks. The survival rate is very low because the chicks require a LOT of fish, and it is difficult for the parents to feed multiple chicks (they have to fly out and catch fish one by one, and sometimes other adults steal fish from each other). Also a lot of the time, the fish they bring back are too big and the chicks cannot eat them (they eat by swallowing the fish whole, and many species such as Butterfish are often too large for the chicks to eat). I'm not sure why the adults sometimes kill their own chicks, but I think the difficulty of raising/providing for chicks has something to do with it. They don't eat their own chicks, but they will sometimes leave the dead chick in the nest as additional insulation for the remaining chicks. Not only are the chicks in danger of starving or being killed by their parents, they also have many natural predators at all their life stages (they are never safe, even as adults). Many species of terns are listed threatened because they have very particular habitat needs. Seavey Island is one of the few places on the NH coast where terns can live, and that is why we work there: to make sure that the tern populations there continue to thrive. They wouldn't be able to without the tern restoration project's efforts.
ReplyDeleteSometimes we try to help chicks but most of the time, if they are chased out of their nest by their parents or aren't getting fed, they won't survive because if they wander into another nest those parents might attack and kill them, and chicks are unable to feed themselves until well after they have learned to fly.
So far the tern project has been very successful; the population size has been growing steadily every year. Here are a couple links to information about the project:
http://www.sml.cornell.edu/sml_ternproject.html
http://www.wildlife.state.nh.us/Wildlife/Nongame/projects/ternRestoration_project.html
Posted By Johanna Brophy
Is the control of infanticide in these animals understood? What signals tell adults to eat and/or consume other's young? What tells them to consume their own? How much of these are drives, and how much come from external input? (Perhaps other birds are too intimidating to attack their young?)
ReplyDeleteBy Joseph Needleman