This season it’s back to the island of Stora Karlsö in the Baltic Sea to join the dedicated team of seabird researchers doing research on (you guessed it) seabirds!
Upon arriving at the island it was straight to work studying the diet and provisioning of common murre chicks by staring down a ledge with breeding individuals and recording size and species of fish brought to the chicks for an entire day (from 3:00 to 23:00). Time spent at the nest with chick and partner were also noted. This kind of study allows us to understand what the provisioning effort is to chicks and to see what parental strategies are most successful (e.g. raising the chick to fledging size). Behaviors such as not incubating the egg or not feeding the chick often enough, or even trampling the chick to death while bickering with a ledge neighbor are some examples of birds wasting the energy they invested in breeding this year. Typically, common murres lay one egg in the breeding season and it is rather rare for them to re-lay if they lose their egg.
|Rebecca Young (left) and PA Berglund (right) entering data from the diet study on a sunny day.|
This year we suspect, due to late laying dates and the fact that more experienced (e.g. older) individuals are electing not to breed, that it will be a ‘bad’ year. That is, we don’t expect as many chicks as usual to fledge and that therefore breeding success this year will be lower than in the past. In fact, when we checked the records, we saw that this year was the latest on average laying date in a decade! Too soon to say anything conclusive about why, but hypotheses we have floated so far include a bad winter (e.g. that the birds returning to breed do not have the energy to do so), low fish quantity or quality in the breeding area, and even abiotic factors.
There are several related monitoring type studies that take place concurrently on Stora Karlsö. One of these is ring resightings. Several different areas on the island are used and for 45 minutes a researcher reads the rings of common murres located in these areas, with the aid of a scope or binoculars of course. One such researcher who uses this kind of data is Blanca Sarzo, PhD student, who models common murre survival.
|Blanca Sarzo entering ring resighting data into one of two field computers.|
The main reason that Tom Evans and I return to Stora Karlsö, however, is for collecting tracking data. This year we’re focusing on maintaining and laying groundwork for long-term annual tracking of common murres to take place on the island. This is feasible given the artificial ledge that allows us to be close to the birds without disturbing them, which in turn allows us to keep tabs on who is breeding with whom and whether they have had a tracking device on them in previous years. We aim to put devices on the same individuals as much as possible since this allows for individual repeatability studies and direct comparison between years.
Before you can track birds, however, you need to prepare the devices. This can mean anything from maintenance to configuration and (as we work with diving birds), waterproofing. It is essential to the mission, therefore, to set up a servicing station.
On the left, the soldering and waterproofing station. Top right, a GPS device charging. Bottom right, 2 GPS devices that are ready to be put on a bird.
The next step is, of course, to catch a bird. Depending on the day and mood of the birds this can be quite a long period of waiting around for the right bird to sit on the chick. As we also bleed the birds for aging studies conducted by Rebecca Young (Baltic Seabird Project) we focus on birds that we know the exact age of and have had GPS devices on them previously. These are then caught by nose pole in the artificial ledge and processed there as well. We take several measurements, bleed them, collect feces and tick samples for a study conducted by Michelle Wille from Uppsala University, and lastly attach a GPS device using tesa tape to the back of the bird. After that it’s time to release the bird and check when it returns to the colony to attend its chick.
|Aron Hejdström (right) taping a GPS device to the back of a common murre while I (Natalie Isaksson) hold the bird in position (left).|
Common murre with GPS device on its back outlined in red!
Last year we put TDR’s and GPS devices on several razorbills. There is no chance of recovering a GPS the following year as they are only attached to the back feathers with tesa tape and if the partner does not preen the device off eventually, they will moult it off after the breeding season. However, we attached TDR’s on the legs of the birds with plastic rings so it is possible to recover devices the next year in case the birds are not re-caught the previous year. It is therefore part of my work this year to as many of the razorbills as possible from last year and retrieve the TDR’s from them. A few days ago we successfully caught the first razorbill of the season and removed its’ device from last year. One down, five to go!
Tom Evans holding razorbill 8114406 with TDR still visible attached to the yellow plastic ring on its’ left leg. Rather unusually, this individual did not try to bite Tom’s fingers off.
Until next time!
Photo: Natalie Isaksson