Summer torpor and status changes...

Things have really quietened down on the bird front and the only highlight of a longish walk this morning was a Little Egret on the river. This is the first June record in the parish for a species which has dramatically changed its status. The first sighting was less than ten years ago and subsequent records were restricted to the odd late summer bird on the Swale (a couple of ringing recoveries point to these being birds from the Nottinghamshire breeding population). Last year numbers peaked at five birds and this year they have been seen in every month except May.

Given the rapid expansion of the egret population in the UK an increase in local sightings perhaps isn’t particularly surprising but I’m always intrigued why some species numbers fluctuate.

To take a couple of examples…

Tree Sparrows.
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This species saw a dramatic crash in numbers from the 1970s and this was reflected in the parish, they were a distinctly difficult bird to find when we first moved here in the late 1980s. The last few years, however, have seen a rapid increase and they now outnumber House Sparrows (even in our garden). It’s not clear to me what has changed in those years to (partially) reverse their decline?
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You also get unexplained short term swings e.g. in 2014 Garden Warbler numbers (the bird above was pictured in Morton last year) exceeded those of Blackcap but this year the latter are by far the commoner species. Why?

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This smart male was photographed in the Magic Garden