Gannets usually don’t start breeding until they are at least 5-years-old. This means that after fledging they spend 4 or maybe 5 summers just having to look out for themselves. During these ‘teenage’ years they gradually loose the dark plumage they have as fledglings, find themselves a partner and establish themselves at a colony in readiness for their first attempt at breeding. However, beyond the behaviour that can be observed at colonies, we know very little about the foraging behaviour of these young gannets. This is something we are keen to address. Learning about where they go and how they learn where to forage during the breeding season has important implications for safeguarding gannet populations into the future.
So after a couple of trips honing our skills catching adult gannets it was time to try our hand at catching and tagging some immature birds. This was to be something of a first on Bass Rock and is one of only a small handful of studies looking into the foraging ecology of young seabirds so it’s really exciting research to be involved in!
The primary reason immature gannets haven’t really been tagged before is due to the difficulty in getting the data back. As I mentioned in the post ‘Gannet Grabbing’, the GPS tags most commonly used for high resolution (fixes at short time intervals) bird tracking require the bird to be re-caught in order to retrieve the device and access the data. Unlike breeding adults, immature gannets don’t have a chick or nest site to defend so predicting when, where and even if they would return to the colony could be anyone’s guess. Fitting them with traditional GPS tags that may never have been retrieved just wasn’t worth the risk.
Fortunately, technology in the field of animal tracking is developing fast. For our work we have chosen to use GPS tags with RF (radio frequency) capabilities meaning that, providing you can get close enough, you can download the data from birds without the need to re-catch them.
Now, if you’ve ever been lucky enough to land on the Bass Rock in recent years, or even if you’ve taken a boat tour around the rock you’ll know that the entire rock is covered with birds, almost every square inch has a gannet sat on it. As soon as you step onto the helicopter landing pad the alarm is raised and the panic spreads. Before you know it the gannets are off, scrabbling over the rocks and each other trying to get some air under their wings to take them away to the safety of the water. The gannets in this area are all immatures and non-breeders meaning there’s nothing is stopping them from making a break for it as soon as you arrive.
Fortunately for us, this is not the only area that immatures and non-breeders can be found. Deeper into the colony, as you make your way from the lighthouse to the ruined chapel above, non-breeders can be found on the path and the slopes in-between, as well as on the steeper rocky slope above the chapel itself.
Having been wondering for years whether it would be possible to catch an immature bird and waiting for the technology to advance enough to make it worthwhile, my boss Keith was not going to miss this challenge. So, one sunny morning in mid-July, armed with the pole and noose, Keith set about catching the first immature bird on Bass Rock. It turned out to be easier than expected which was a big relief! We initially targeted older immatures (4-5 yrs) who looked to be holding a territory (establishing themselves in readiness for the next breeding season) as we thought we’d have more chance of them returning so that we could download the data . It wouldn’t have been ideal if we deployed the tags on birds that then left and didn’t return for the rest of the summer. We were hoping for the tags to have a transmission range of up to about 8km so we definitely needed the birds to come back to Bass. However we did then decide to tag some younger 3-year-olds but left the younger birds to Dr Jana Jeglinski from the University of Glasgow who, as you’ll find out next week, is using some different tags to answer some slightly different questions about the lives of young gannets.
The day was a resounding success with 8 immature birds caught and tagged. Heading back across to Seacliff in the boat it was smiles all round again. It’s hard to describe the buzz you get from a great days fieldwork but we all felt it. Now it was just a case of waiting and hoping that the tags would work as planned. Fortunately we didn’t have to wait long, two days later we headed back to the North Berwick coast, held our breath as we connected the equipment and then success – the downloads began and we had foraging trip data from immature birds on Bass Rock for the first time ever! (The only slight disappointment was that the range of the tags wasn’t enough to allow us to download them whilst sitting on the balcony of the Seabird Centre enjoying coffee and carrot cake, but you can’t have everything can you?!)
Thanks for reading, if you have any questions please feel free to post them in the comments, I’ll be happy to answer them if I can.
Next week a post from Jana about her work tracking immature gannets.