So I realised I haven’t really gone into any detail as to how I’m spending my days and why. Cue a couple of slightly more science-y posts. You’ve been warned. For this project we’re using the full spectrum of data collection techniques; from very simple and easily repeated sampling in the field, to brand new and genuinely cutting-edge tracking devices. The telemetry is pretty cool and sexy, and is already showing us facets of the white-front’s lives that would be simply impossible to see otherwise. But, you’re going to have to wait for next time to hear about that! For now I’m going to explain how and why I’ve spent a fair bit of time ageing the birds here on Islay, and why I spend a couple of days every fortnight looking solely at goose bums. Yes. I do.
Adult Greenland white-fronts enjoying the Islay sun - it's a surprise, but you have to make the most of it!
We can, therefore, estimate any given individual’s body condition simply by looking at its bum and giving it a rating, or scoring, against some pre-determined scale. And we have one of those – made earlier of course. It’s called the Abdominal Profile Index (API) and is the basis of a lot of what I’m up to. The beauty of the API is that (with an experienced eye for a goose bum!) it is extremely quick and easy to score the body condition of large numbers of individuals – and from a distance.
When your diet is almost entirely vegetarian, it can take a lot of work to put on weight. Eating high quality food, and/or being able to spend long periods of time feeding mean an individual can fatten fairly easily. However, it may be that there is variation in the ability of individuals, flocks or even populations to access sufficient food resources to put on weight – and, if so, we would expect to see variation between their API’s as a result. Have a quick look at white-fronts in the photos; you should be able to see a clear difference in the size and shape of their bums!
This variation is most visible and important during the autumn and late winter/early spring, when the geese are feeding up rapidly just after and just before migration – to recoup the fat lost on the way here and to put on those extra few pounds prior to leaving. At other times of the winter, being very fat isn’t necessarily a good thing – being heavy slows you down and makes you less manoeuvrable, in turn making you more vulnerable to predation. The geese respond by regulating their body mass during the middle of winter – storing fat, but not compromising their survival.
We are looking at API variation at three scales with the Islay white-fronts. The first is between populations. The API’s on Islay as a whole can be compared with the birds that winter at Wexford in Ireland – a population that is doing much better than any other. If Islay API’s are significantly lower than Wexford, especially at migration departure point, then that would suggest the Islay birds are being restricted by their wintering site. The second scale is between the different flocks (or sub-populations) here on Islay. This will help determine if some flocks are unable to access resources as well as others; which will tie in neatly with work we’re doing characterising the habitats the white-fronts prefer (and where it’s available) and recording disturbance levels through the winter – both potential causes of body condition variation. The third scale is at an individual level. Having a number of neck-collared birds means we can follow and individual’s body condition through the winter and relate this precisely to the areas and habitats they’ve used through the winter.
a family group in Iceland. Spot the juveniles!
2 juveniles with a parent. One in the background too!