A clear calm interval on Saturday morning gave us the opportunity to visit the Spring ride at Leighton Moss RSPB Reserve. The first round of our six nets produced a good variety, including a Cetti's warbler and a Nuthatch and four Sedge Warblers these were weighed and none showed any sign of fat. The average weight was 10.7 grams. The next round produced two more Sedge Warblers one at 10.2 with a fat score of 1. Kevin extracted the other and was amazed when he examined it , its body was completely covered in fat including the breast and he gave it a fat score of 8. We all guessed at its weight and the highest suggestion was 16 so we were all amazed when it came in at 19.3.grams. When I entered this weight on IPMR it came up with a warning that the usual highest weight was 17.9. So quite an intriguing bird
According to the migration Atlas Sedge Warblers mainly fatten up for their journey across to France along the English south coast or the South Wales coast. We have ringed as a group just over 14,000 Sedge Warblers so just about impossible to search through these but we only occasionally get birds above 13 grams. However a search of September catches revealed one at 15 grams in late September and this appears to be the heaviest we have recorded up to now.
It is thought that Sedge Warblers fatten up on Plum/reed aphids which is abundant in many parts of the reed bed this year. But it is still amazing that this bird should accumulate so much fat especially when only one of the 89 other birds caught this year so far, exceeded 13 grams and that by .1 of a gram.