So as promised in my last post, I’m handing over to Dr Jana Jeglinski from the University of Glasgow this week. As you’ll find out, it’s not just myself and the University of Leeds team that have been tagging immature gannets this summer. Jana has been doing the same, not just on Bass Rock but at a couple of other European colonies too. Read on to hear more about her exciting work.
Seabird colonies during the breeding season are a full-blown, multi sensual impression, if not impact, of movement, noise and, if you are (un)lucky to be close enough, smell. First your eye takes in everything at ones, birds swarming the sky around the colony like bees and clinging to cliffs literally everywhere. You give yourself time and you will see that this seabird city, this large entity is really made up by tens of thousands of individuals, pairs that work together to bring up their chick, shuttling to and fro from foraging grounds, bringing fish and nesting material, disputing with neighbouring breeding pairs and dealing vicious blows towards unlucky intruders into their miniscule breeding territory. You see some birds clustering at the fringe of this bustle, obviously not breeding, but peering with long necks around, and wonder what they are up to. You can spend hours just watching.
Colonies like this have long been thought to be separate entities, more or less likened to populations, with their own dynamics and their own characteristics. This is reflected in the design of many ecological studies, which are interested in aspects of the behaviour and ecology of breeding birds in one colony, or compare these data between different colonies. For most adult breeding seabird species, the concept holds true: once you have established your breeding territory you are likely to spend the rest of you life breeding in this colony, or trying to. For Northern gannets, we know that this segregation between colonies extends also to foraging grounds– adult breeders from different colonies are unlikely to meet each other during their foraging trips as the foraging ranges are highly segregated1. There is also a general understanding of high natal site fidelity – you are likely to breed in the colony in which you have been born.
A two-three year old Northern gannet defends itself against a neighbouring immature bird. Site ownership is still transitory in this age class, and both immatures might have left by the evening exploring other colonies.
The problem with the concept is obvious, but surprisingly hasn’t found much general attention to date: how do new colonies come about? And why do we observe young colonies to grow much more rapidly than their own production of chicks would allow them to2? The Northern gannet population offers a great illustration to these puzzling questions, having been exploited by large scale harvesting of eggs, chicks and adult birds for centuries, and having recovered since protection around 1900 from a population size of about 70.000 to more than 440.000 breeding pairs and from 16 colonies in 1900 to 51 in 2014 in their North-eastern Atlantic distributional range3.
The key to answering these questions is an almost completely overlooked age class in ecology: teenagers. We might know a lot about chick survival until fledging and about adult foraging strategies, but there is a gaping hole in our understanding of much that goes on in between. For a gannet the hole is big, covering four – five years, because gannets only start breeding at an age of about five tears or older. As it turns out, this gap is also very important for understanding seabird population dynamics. Information, e.g. from ring resightings and from a single tracking study4, shows that these young prebreeding birds spend the summer months investigating breeding colonies, the one in which they were born, but also others. We call this behaviour ‘prospecting’, checking out potential breeding sites and, first things first, meeting potential breeding mates on the way. A non-ecologists friends face lit up when I explained this aspect of the gannets’ ecology: “A gap year!”
Two 2-3 year old Northern gannets forming a preliminary and maybe lasting bond through ritualised ‘fencing’. Jana Jeglinski
A very long and influential gap year indeed, and one about which we have almost no direct observations and data. The relevance of these prospecting years lies in the decision making process that takes place during these years: where to breed. And with this one decision, taken by hundreds of thousands of first time breeding seabirds every year, ripened over the course of their prospecting years, the whole population can shift and change. A good illustration is the Norwegian Northern gannet population, which did not exist before 1946, because a few birds, amongst them chicks ringed at Les Etac, Ailsa Craig, Grassholm and other UK and Icelandic colonies5 decided to head east and breed on spacious Norwegian cliffs and not in their crowded natal colonies.
Not incidentally, I am specialised in and passionate about the ecology and behaviour of young animals, which is why I chose to investigate the prospecting behaviour and space use of immature Northern gannets during my Fellowship at the University of Glasgow. One of the reasons we know so little about this age class is their elusiveness – they might be spotted at the fringe of breeding colonies in so called club-sites, but take off at the least disturbance, or might catch our eye fleetingly out at sea, but that’s not much basis to an ecological study. For real insights into immature movement, we need advanced technology.
I am using GPS GSM tags, one of the cutting edge developments of biologging technology. These small electronic instruments can be programmed to collect GPS positions at predetermined times, and to store these positions amongst other sensor readings, for example flight height, temperature or salinity. They also have a solar panel to reload their battery so that I can deploy them for months at a time. What makes them uniquely suitable to my work is that they also transmit data: equipped with a sim card with roaming ability, they detect mobile phone coverage and send me the data they have collected using the mobile phone network. The reward for deploying these tags on immatures, by no means an easy task, is leaning back and receiving text messages from teenage gannets!
One of the study animals with a GPS GSM tag glued onto of the tail feathers with white TESA® tape. This deployment method is common practice and has been tested in many studies, showing minimal impact on the birds if the tags are lightweight enough. My tags weigh 37g, about 1.3 % of the body weight of the study animals – only half of the suggested upper limit of 3%. The dark top of the tag is the solar panel, which allows the tag to recharge its battery over the next few months. Tail deployed tags fall off when the birds moult their tail feathers, approx. 2 months after deployment.
I am currently working in three different gannet colonies in Europe, together with collaborators from the Centre for Ecology and Hydrology, the University of Kiel and the Research and Technology Centre Buesum in Germany, the University of Leeds and the University of Exeter. The Bass Rock, the largest gannet colony in the world6, is one of my study sites, with kind permission of the Dalrymple family and organisational support of the Seabird Centre, working together with Prof. Keith Hamer’s group from the University of Leeds. Keith’s PhD student Jude Lane (@heyjoode) and PostDoc James Grecian (@JamesGrecian) and I, sometimes accompanied by Maggie Sheddan, would travel out to the Rock, safely transported by Robbie and Jack Dale, spending the whole day helping each other capturing, taking notes and deploying tags – a great team working experience! The Bass Rock is, through the sheer size of the colony but also the number of historical buildings on the island (now mostly occupied by gannets!) an amazing and literally breath-taking place to work.
Having long gotten used to side effects such as smell and dirt, I as most other ecologists, adore fieldwork and the deeply insightful bliss of being with and amongst our study species in their habitat. We usually settle with a somewhat resigned air back in front of our computers once the field season has passed. I currently find myself almost skipping to the office every day, brimming with excitement to connect to the server and find another data package received, another aspect of the hidden years revealed!
The year until next field season will see me analysing the tracking data of the immature gannets in detail, investigating the range of their movements and the frequency of their colony visits and why they might visit certain colonies but not others. The results of my analysis and more tracking data collected next year, will then allow me to integrate the network structure of the gannet breeding colonies into a model to understand better the drivers of the dynamics of the gannet metapopulation. We are also investigating a very applied question when investigating the space use of immature Northern gannet. We are looking into the overlap of immature gannet habitat use with anthropogenic use of their marine habitat, particularly offshore windfarms – a particularly relevant topic for the birds travelling to and from the Bass Rock and the German colony on Heligoland in the North Sea. My preliminary data already shows that immature birds use space very differently than adults do, and for a holistic understanding of the effect and impact of anthropogenic change to the marine environment it is paramount to include all relevant age classes.
To hear more about my work, you can follow me on Twitter: @JWEJeglinski
References and further reading: 1 Wakefield et al (2013) Science, 2 Moss et al (2002), 3 Jeglinski et al. in prep, 4 Votier et al. (2011), 5 Barrett & Folkestad (1996), 6 Murray et al (2013) Scottish Birds