The Importance of Spring Staging: Why do female geese get fat faster?

The numbers on the y axis are body condition scores (our scale goes from 1-7). The start period was mean API measures for all individuals resighted between 01/05/2013 and 03/05/2013. The end  period was mean API measures for all individuals resighted between 26/05/2013 and 28/05/2013.

We talked quite a lot about measuring body condition towards the end of the time we were in Iceland. One thing that is particularly apparent towards the end of the spring is the big difference in API within each pair. As this graph shows this is because females are leaving in Iceland in much better condition than males. We've known this is the case for a while, but its nice to be able to show it with my data! Little results like this help to show that while you may have gone crazy whilst collecting all the data, you were doing a reasonable job still......

Clearly, females have to make more of an investment in reproduction once the birds arrive in the Arctic so have to leave their spring staging areas with more fat reserves. There is not much for a goose to eat when they first arrive in the far north, so all the energy reserves they can accumulate in Iceland are of vital importance!

Perhaps of more interest is trying to work out why the males do not end up equally fat...... It seems likely that there might be a cost to being fatter than you need to be, particularly if you take into account just how far the birds have to travel to reach their breeding areas. However, it is also very noticeable during our time in Iceland that there are differences between members of a pair in their levels of aggression and vigilance. It could well be that males are unable to accumulate the same energy reserves as they are spend more time engaging in these social behaviours to enable the female of the pair to forage more efficiently. This seems to be backed up by the fact that the Whitefronts that colleagues study just up the coast are very similar in this regard.

It is also very apparent that the birds left Iceland in much better condition this year than last spring - hopefully that bodes well for a successful breeding season!

Spring 2013 social network

Map of social interactions for Alftanes and nearby areas in May 2013

After a good few weeks of painstaking data entry and shuffling excel spreadsheets around, I'm finally in a position to see what some of our data from this spring looks like! Its amazing to think how much work goes into producing a social network like this!

Its good to see that its is broadly similar to last years social networks, although the shift in home range of LIRY and LHRY (a pair of geese I know well from Dublin too) half way through the spring from Hafnarfjordur to the President's Fields on the main peninsula has resulted in the network being more cohesive overall.

[LIRY and LHRY are the two red nodes sitting halfway between the main "red" social cluster and the "blue" social cluster]

The end of spring....

In the last few days Greylag goslings, Eiderlings (not sure what else you'd call a baby Eider?) and the family of Whooper Swans pictured below have all made an appearance on Alftanes - very much a sign that May is coming to an end and the Brent will be on their way soon.

The geese are all now looking very fat - and everyone up here seems to be in agreement that they are ready to go. This is borne out by the fact that the vast majority were just sat around, loafing this morning (hence why I'm back at base writing this). It seems likely that a change in the weather is all that required. The last few days have largely been fairly miserable with drizzle, squally showers and often strong winds making doing fieldwork a real pleasure. I'm hoping this will happen before I leave on Wednesday morning as it would be really cool to see!