One of the fascinations of ringing the same site over the years is the ability to compare years to get an idea of the population trends and productivity of the species you study. At Leighton Moss RSPB Reserve our main study is the isolated population of Bearded Tits. This year has been good, for so far we have ringed 54 juveniles compared to 48 in the whole of 2013 and just 11 in 2012 and there is quite a time to go yet.
The main spin off of this study is the RAS we run on Reed Warblers. Our initial feeling was that the breeding population was down somewhat but this month they have bounced back with a total of 517 handling's compared with just 281 in July 2013 and an average of 380 over the past three Julys. This suggests excellent productivity. To date we have caught 153 adult Reed Warblers, this compares to an average of 190 over the 17 years of our study. We usually catch fewer in August as adults start to leave early in the month. The only two adults that we caught this morning were obviously preparing to leave for they had fat scores of 2 and 4 and were well above average weight, don't think they will be going anywhere over the next two days if the weather forecast is anything to go by!
By contrast Sedge Warblers are well down with only 79 ringed compared to 182 in the same period last year. There is only a comparatively small breeding population of Sedge Warblers at Leighton. Recoveries suggest that most of the birds we catch are migrants from further north. Perhaps they are later this year or possibly weather for migration has been so good they have not had to stop off at our site. Willow Warblers fall into the same category being mostly migrants . This July we have ringed 114 compared to 85 last year.
In case you are thinking that some of the recorded changes from year to year are due to varying effort-we ringed on 18 mornings in 2013 and 17 this year.