How bird-ringing can be used to determine lethal effects of marine stressors.
Black-legged kittiwakes on their nests showing off their metal rings and code rings, which are easily readable with binoculars. Photo: Tone K. Reiertsen/NINA.
One of the goals of the MARCIS project is to be able to determine the effects of human activities on seabird populations. To be able to do this the project depends heavily on long-term monitoring data of seabird survival and population change. These unique data series have been collected through seabird annual monitoring programs. Bird ringing and resighting of ringed individuals between years is a part of this work, and allows us to calculate yearly survival rates of breeding adult seabirds, and consequently identify the lethal effects of the various marine stressors they face.
The 2022 field season for seabird monitoring is well under way. Several of the MARCIS project participants are heading out to colonies where long-term monitoring is conducted along the Norwegian coast as part of the SEAPOP monitoring programme (https://seapop.no/en/activities/key-sites/). I am heading out to Hornøya, a bird cliff in north-eastern Norway, home to around 100,000 seabirds. Several of the species that MARCIS will focus on breed in this colony.
Hornøya bird cliff, a scenic home to many breeding seabirds including Black-legged kittiwakes, Brünnich guillemot , Atlantic puffins and Common guillemots. Photo: Kate Layton-Matthews.
A key part of the annual monitoring is ringing (or banding) of birds with a metal ring with a unique ID, and a plastic ring with an individual colour or code combination. Thanks to this individual code, we can resight the same birds the following year using binoculars and collect information on whether they have returned to their colony and survived from one year to the next.
Seabirds are long-lived species (for instance a Common guillemot aged 37 was observed this year at Hornøya, while the record is 42 years for guillemots and 45 years for Atlantic puffins) and so their ‘life-history strategy’ is focused on their own survival, rather than, for example, producing a large number of chicks. They therefore usually have a high survival rate, which doesn’t vary much from year to year. However, we know that changing environmental conditions and emerging threats can reduce their survival. Causes of mortality in seabirds include changes in prey availability, weather conditions or other climatic conditions, as well as mortality caused by human activities such as over-fishery or bycatch, collision risk with offshore wind farms or risk of oil-spill. All of these can have lethal effects on seabirds, and several of these ‘stressors’ will be studied in MARCIS.
Combining knowledge of seabirds’ distribution throughout the year from tracking-data, with annual survival rates from bird-ringing data and data of the different stressors seabirds face during their annual cycle, can provide us with new knowledge of what affects their ability to survive.
Survival is the key factor determining changes in seabird population sizes, as a consequence of seabirds being long-lived birds. Having precise estimates of survival for the focal species in MARCIS is fundamental. It allows us to model the consequences of industrial stressors on this key parameter, which ultimately determines changes in population trends.
In addition to ringing birds, we also measure several indicators of individual seabird’s condition, such as biometric measurements. We also monitor seabirds’ diet to understand how they are linked to the marine environment, which may help us explain the differences we observe in survival rates.
A field assistant weighs a kittiwake and measures its wing length, two important measurements when ringing a bird for the first time, that help us understand more about their condition on capture. Photo: Kate Layton-Matthews.
So, after we’ve finished deploying new rings, and collecting the data we need from each bird, all that’s left is letting them go and they are ready for resighting in later years. We then hope they have a successful breeding season and migration back to their wintering grounds, in some cases, all the way across the north Atlantic, to Greenland or north to Svalbard.
Happy field season everyone!
Vardø lighthouse is our field station during the seabird field season on Hornøya. Photo: Kate Layton-Matthews.