|A fairly average looking male Siskin for comparison with the bird below (both caught today).|
|This is a particularly bright and intensely coloured individual.|
The retraps from February and early March are intriguing as their weights haven't changed all that much and the little change there has been can be attributed to normal diurnal variation rather than any pre-migratory fattening. Age doesn't seem to be a factor as one of these long stayers is an adult male so perhaps they are just going to be late migrants that will fatten up in due course.
Despite some retraps showing little or no weight gain the proportion of heavy birds in catches has been increasing with 8 of the 9 birds caught this afternoon having substantial fat deposits and a weight range of 15.1g to 16.3g. These very heavy birds are likely to be going back to breeding grounds on the continent rather than in Scotland. The lighter bird from today was one of the retraps referred to above and weighed 13.1g at 18:30 compared to 11.9g at 07:30 when ringed on 5th March. This change of 1.2g fits in with normal diurnal weight changes and had it been caught at the same time on both days it may well have weighed the same, or very nearly so.
|Fat Female Siskin|
|The lump is the birds crop full of seeds but it is also covered in a layer of fat which extended across the back of the neck.|
|Blowing back the feathers on the throat reveals the tracheal pit bulging with fat (appears pinky-orange compared to the deep red of the breast muscle).|
|Blowing back the feathers of the belly also reveals a thick bulging layer of fat.|