Alaska Science Center
Seabirds gather their food from the sea either by themselves or in large feeding flocks. Most seabirds rest and sleep on the rolling waves, while others roost on land for a few hours a day. But all seabirds must return to land to lay eggs and raise their young. When seabirds gather on remote islands and rocky outcroppings, they form what we call a colony.
We are able to study seabirds both on the open sea and on their colonies.
All most people ever know about seabirds comes from watching them at their breeding colonies. Scientists are no different; observations at the colony form the foundation of what we know about seabird biology. Colony work gives answers to questions such as; How many seabirds attempt breeding each year? How many chicks do parents produce? And how hard did the parents have to work to raise those chicks?
But without understanding what seabirds do at sea, we would never completely understand their biology. Without adequate food, seabirds cannot raise chicks and they might not even be able to sustain their own life... and everything seabirds eat comes from the sea.
Thats why our project includes pelagic seabird surveys (pelagic means non-coastal parts of the ocean). We use a number of different vessels for this work, but we always follow a similar protocol. First, we plan a grid of lines on a chart of the waters we want to survey, representing an appropriate sample of the area in question. We then post sharp-eyed observers at a good vantage point on the vessel, while slowly motoring along the selected gridlines. Observers note down all the seabirds seen within a predetermined strip, and sometimes we simultaneously record fish densities using hydroacoustics. Pelagic surveys can be extremely exciting when we encounter areas of high seabird densities, like in passes between islands in the Aleutian chain where we see hundreds and hundreds of auklets swarming like insects on the water, attracted to food brought to the surface by the boiling currents as moving seawater is forced through the island passes.
When the surveys are over, we end up with lots of new information. We learn where and when seabirds concentrate at sea, and (as fishermen have always known) how those concentrations relate to what is going on under the oceans surface. Lately weve begun using oceanographic sampling gear and satellite images of the oceans surface to link seabird concentrations to factors like the temperature and salinity of the seawater. We also identify the location of ocean features called fronts- where two water masses collide.
Life on a seabird colony is crowded! At the beginning of each summer, hundreds to thousands of seabirds pack together to nest on remote islands and coastal bluffs. They do this because there is safety in numbers and the whole colony is alive with breeding activity, which encourages the birds to nest.
Each seabird species has its favorite habitat on the colony. Some prefer beach rubble and boulders or the cracks in a cliff face. Others nest side by side on rocky ledges. Some seabirds dig a dirt burrow into the soft soil at a cliff edge. Still others nest on the flat ground at the top of the colony. Many seabirds return to the exact spot that it nested on last year.What We Learned
Seabird colony populations change all the time as adults die of old age or from un-natural sources of mortality (like oil pollution, or drowning in gill-nets), young birds mature and join the colony to begin breeding, or because birds change their breeding sites. Because seabirds typically gather in large, multi-species colonies, it is relatively easy to count their numbers during the summer breeding season. At small colonies, we might count all the birds present at one time. At large colonies with hundreds of thousands or millions of birds, it is impossible to count all the birds, so we typically count numbers in smaller sub-areas and use these data to estimate population trends. Censusing is vital to monitoring the status and health of seabird populations, and provides a key source of information for researchers and managers.
One way that scientists try to understand how seabirds are affected by changes in the marine environment is by studying their breeding biology. Seabirds spend most of their lives flying across the ocean, resting on the ocean, or swimming beneath the surface. But they must return to land, usually islands, to lay eggs and raise chicks during the annual breeding season. These islands are often very small, but they may support hundreds of thousands of birds that have come from hundreds or even thousands of miles away to nest there. These islands are often very remote and inaccessible, however, if they are accessible, having large numbers of birds in a small area makes it easier for biologists to study them.
By observing the birds on land when they are breeding, we can get an idea of how healthy that group of birds is at that point in time. This also tells us a lot about what is going on in the ocean. If there is a lot of food (mostly forage fish) around the colony, then the adult birds will be healthy, many of these young will fledge from the colony. No single observation paints the whole picture so we collect a lot of detailed information to determine how well the birds and their marine environment are doing. Some examples of the information we collect are: how many chicks are raised by each pair of birds, how fast the chicks grow, adult and chick diets, adult time budgets, adult stress levels, survival rates, and genetics.
Knowing what birds eat is an important part of understanding their behavior and survival. Seabirds eat small marine fish, squid, shellfish, and a variety of crustaceans (such as krill and crabs). Since some foods may be better than the rest, we want to know what kinds of food seabird adults and chicks are eating.
Seabird parents capture prey at sea and bring it back to their chicks. We study chick diets according to how each species feeds its young. Puffins, pigeon guillemots, common murres, and murrelets carry whole fish (or sometimes squid), in their bills to their chicks. We crouch in hidden blinds and watch the adult birds as they fly back to the colony to feed their chicks. With binoculars we can identify the fish they carry and get an estimate of its length in relation to the length of the birds bill. Kittiwakes and gulls feed their chicks differently. They swallow whole fish for their chicks at sea. When they return to the colony, they regurgitate this food for their chicks. We collect some of these regurgitations and analyze their contents to learn about their chick diets.
To learn more about the different ways that seabirds catch their food, look at the seabird flash cards.
Just as a busy mother or father must carefully manage their daily activities between work, parenting, grocery shopping, and cooking; seabirds that are raising chicks must also manage their time between various needs. To find out how much time a bird spends each day out at sea finding food for themselves and their chicks, and at the nest keeping their eggs and chicks safe and warm, we study their "time budgets". One way to look at seabird time budgets is to measure their presence and absence from the nest or colony.
The amount of time birds spend looking for food is called a foraging trip length. The measure of how much time birds spend at the nest site is called site attendance. In our study, we assume that kittiwakes and murres are out finding food if they are absent from their nest sites. So, if there are differences in foraging trip lengths or site attendance, we would suspect that birds were having a more difficult time finding food, or were having to fly further to find fish to eat.
We use two different methods to study time budgets. The traditional method is direct observation- sitting in blinds and recording the arrivals and departures of birds at the colony and the rate at which they feed their chicks. We also use radio telemetry to get more comprehensive data on time budgets. By attaching tiny radios to seabirds and using a computer receiver to log their presence or absence, we learn how much time radioed birds spend at the colony or away looking for food.
Stress is something we can all relate to in this day and age. For seabirds, one source of stress comes from the daily effort involved in locating and acquiring food-- both for adult seabirds and for their hungry chicks. We are interested in how stress is related to the availability and abundance of food, and how stress may impact other aspects of their biology such as the deposition of fat reserves, growth and development of chicks, and survival after the breeding season.
We actually measure stress by taking a small sample of blood from birds immediately after we capture them for banding and measurements. The blood is preserved and later analyzed in a laboratory to measure glucocorticosteroid hormone concentrations in the plasma. This work is done in collaboration with scientists at the University of Washington in Seattle.
The sexes of the seabirds we study are indistinguishable by the human eye; any size differences are only very slight, and the feather patterns of males and females look the same. To understand seabird colony dynamics, its important to consider the influence of sex on time budgets and survival. So to recognize male and female birds, were using a technique developed by scientists at the University of Glasgow in Glasgow, Scotland.
In using this technique, we take a blood sample from every adult bird we capture and handle. Molecular analysis of those blood samples in the laboratory produces a picture of specific pieces of bird DNA. Since female birds have two different sex chromosomes, their DNA shows up as two bands. Males have duplicated chromosomes, so only show one band (see Figure).
Well soon know the sex of every bird weve banded at our study colonies, giving us better insight into how the colonies work. Future genetic analyses may also tell us more about how seabirds are related to each other, and how their populations interact.
The value of an individual birds life is usually measured in terms of its Lifetime Reproductive Success, or LRS. If one bird manages to raise two chicks during its lifetime, while another bird raises ten chicks, the second bird is obviously much more successful. Raising as many chicks as possible during a birds lifetime is referred to as maximizing the LRS. But different species of birds use different strategies to maximize their LRS... some species try to raise many chicks each year for only a few years, while others raise only one or two chicks per year for many years. Birds that try to raise lots of chicks each year tend to live relatively short lives, while birds raising small numbers of chicks tend to live longer.
Nearly all seabird species share a similar strategy for maximizing their LRS, laying only one or two eggs each breeding season and living very long lives. The albatross are extreme examples of this common strategy- some albatross species attempt breeding only every two years or so, and they require many months to raise their chick... but an adult albatross may live fifty years or more! Of course, if an albatrosss life is cut short for some reason it will end up with poor LRS, and its strategy will have failed.
Since were trying to understand what factors influence the growth or decline of seabird populations, its important that we know more about the survival of the seabirds we study. Thats why weve begun an intensive program of marking some of the adult murres and kittiwakes on our study colonies. By attaching colored bands to their legs, we can recognize or resight individuals from a distance, allowing us to then determine the overwinter survival of each individual. If we have enough birds individually marked, and are able to resight them over a few years, we can calculate the estimated survival rate of the entire population. We can then compare survival rates between populations or between years- for example, one colony with poor local food resources may have poor survival compared to the same species at a food-rich colony. Or suvival may change following a year of particularly harsh conditions, like after an El Nino year.
As biologists we seek to understand the living world with sets of theories that apply to many different communities of organisms. We build these theories by studying actual living things, and biologists know that different organisms and ecosystems are useful for studying different questions about how the living world operates. Thus if youre interested in learning about the genetics of behavior you might choose fruit flies in a laboratory as your study system, but if you want to know about the effect that predation has on animal populations youd do better studying wildebeest and their predators in Africa.
Seabirds are very difficult to study at sea, which is one of the things that makes our project so exciting many of the questions that were interested in about fish / bird interactions are still uncharted territory to scientists. On the other hand, seabirds are ideal for other kinds of studies. Because they concentrate in huge colonies, its easy to catch a lot of them and fit them with colored leg bands that allow individuals to be resighted at the colony year after year. This kind of research allows biologists to explore population biology, which is the study of how birth and death rates affect the growth and decline of populations. This kind of knowledge is fundamental to conservation, among other things, and the population biology of birds was first worked out by now legendary biologists like David Lack and Nigel and Martha Ashmole, who worked at seabird colonies.
Were continuing the tradition of banding adults and chicks at colonies, and the information we get this way gives us a clear idea of why one seabird colony is growing and another is shrinking. And advances in biological understanding and technology allow us to gather vast amounts of information from the birds we handle, information that would amaze the pioneers in our field. Much of the information that were interested in, such as hormone stress levels, genetics, body condition, and survival rates can only be obtained by catching birds.
What We Learned
The adult kittiwakes and murres that we handle return to their nests and succeed in raising chicks at the same rate as other birds in the population. This is due partly to the birds natural resilience, and partly to techniques that we use to minimize the stress that handling causes birds. For instance, some birds, such as Pigeon Guillemots, are prone to abandon their nests during the egg stage, so we only handle these birds after their chicks have hatched, when the adults are more tolerant of disturbance. Other techniques, such as confining a bird in a dark space and minimizing the time we handle birds, can also make the experience much more tolerable for the birds.
What We Learned