Tuesday, 26 June 2012

The Importance of Spring Staging

Once again I've failed spectacularly to keep this blogging lark going... Time for another attempt! June has flown by in a sea of excel spreadsheets. Not that you'd notice it was June, the sun seems not to exist in Cornwall! Anyway, back to geese - with the analysis of our Iceland data in full swing I'll hopefully be able to use the blog to share some our preliminary results. Exciting news from the database is due in the immediate future too...

Iceland represents an essential part of the Brent's annual cycle, and not just a mere stop off on the way from Ireland to the Arctic. The vast majority of individuals spend a month (sometimes more) at various staging sites on the West Coast, building up energy reserves that must not only fuel the next stage of their epic migration, but also a large part of their breeding efforts as well - there is not much for them to eat in the Arctic at the start of June and they must start breeding almost immediately to be able to escape before the winter arrives again!

That means that improving their body condition as much as possible during their spring staging period is essential to being a successful breeder in the summer. As such, it is possible to watch (some) birds gain fat stores at an incredible rate as the spring progresses. Below is a graph that shows changes in the mean API (the method we use to give each bird a body condition score) for individuals recorded on each day of the study period as May goes by for two different "types" of individual. The green line is adults in family parties and the red line is for adults that are in pairs without any juveniles.

The difference between these two "types" of individuals is interesting. They seem to improve their body condition at a similar rate but birds in family parties arrive and leave Iceland in worse condition (the mean for the first day is best considered a blip as it is based on a very small number of individuals). This seems particularly surprising given that family groups are dominant in flocks and so should be able to compete most effectively for resources.

Fortunately, thanks to previous work - mainly by Rich - an explanation is on hand! The poorer condition of adults in family parties is best explained by the fact they have had to "care" for their useless young over the course of the winter. Juveniles are less experienced and struggle to exploit more nutritious intertidal resources as they become scarce during the winter. Families therefore spend more time feeding on terrestrial grassland and maintain worse body condition over the winter months.

The inability of adults to "catch up" in their energy stores means that they arrive at their breeding sites in worse condition and are less likely to be successful breeders. This highlights the huge importance of geese making the most of their springtime in Iceland!!

[Main reference is Inger, R. et al. 2010 Carry-Over Effects Reveal Reproductive Costs in a Long Distance Migrant. Journal of Animal Ecology, 79, 974-982 for anyone still reading...]

Tuesday, 5 June 2012

Long overdue update!

Well so much for more on that later! With the arrival of Team Jameson and ever increasing daylight hours fieldwork got ever more hectic and the blog ending up being neglected...

All of the British and Irish have now returned from Iceland, with Rich and Stephen the last to leave on 1st June. Most of the geese were already well on their way to Arctic Canada by then, with Mummi noticing a big departure from the 26th to the 29th. Certainly during our last week of fieldwork geese were getting noticeably fatter and preparing for the off.

Everyone seemed to have a successful time in the last two weeks of May. Team Jameson managed an impressive number of resightings away from Reykjavik, spending several days based up around Snaefellsnes and also managing lots of resightings from Hvalfjordur and Blautos. Meanwhile the Exeter team continued spending 18/19 hours a day scouring the Reykjavik area for geese and ended up with nearly 5400 resightings and over 340 focal watches of behaviour (that more than 24 hours of watching individual ringed geese!)

Hopefully I'll be able to post pictures and stories from our last couple of weeks up there over the forthcoming weeks. More to come soon?