As many of you will know, I am a trainee bird ringer and have been since 2014. Involved in the complicated process is putting a small, lightweight ring on the leg of a bird, on which is inscribed a unique number. This enables individual birds to be recognised if they are later recaught or found dead, allowing ornithologists to learn more about their migration and biology.
In my four years of being a ringer, I’ve had the chance to ring a wide variety of bird species, ranging from over 100 Blue Tits to some scarcities including Yellow Wagtail, Redstart, Wheatear and Wood Warbler and larger birds such as Stock Dove and Woodpigeon. However, last Sunday’s ringing experience will probably go down as one of my favourites so far.
Fellow Sussex young birder Mya Bambrick and I arrived at Knepp Estate, south-west of Horsham, at 6am. There we met my trainer Tony Davis who had already set up four mist-nets around a field consisting of mainly bramble and willow scrub. This is a fantastic habitat for migrating birds as well as several scarce breeders due to the amount of cover the scrub produces and the blackberries which ripen at exactly the right time to fuel many migratory passerines on their southward journeys. The mist-nests are ideal for catching birds as they are fine enough to be invisible to birds flying between bushes, which fly into the net and fall into a pocket from which they are extracted by licensed ringers.
It was on the first net-round when I noticed that there was something slightly different in the bottom pocket of one of the mist-nets. It didn’t take long for me to realise that it was a Grasshopper Warbler. Grasshopper Warblers, so-called due to their bizarre song which resembles that of a stridulating grasshopper, is a localised breeding species found mainly in fens and coarse grassland and is not often found in high density. However, while researching for this blog post, it was good to learn that they are showing a positive population trend with the UK population experiencing a 23% increase in numbers in the 14 years between 1995 and 2009. This is thought to be as a result of improved survival rates in the wintering grounds of west Africa. Particular preference is shown by British Grasshopper Warblers towards Senegal and The Gambia, which we have learnt from recoveries of ringed birds in those countries. However despite this recent increase, this is in comparison to a proportionally larger decrease which took place in the years prior to that period. Only a few decades ago, this species used to be found in a greater range of habitats than to which it is currently restricted.
Grasshopper Warblers (often shortened to just Gropper) are renowned for the difficulty involved to see them. They have skulking habits, only really coming out into the open when the males sing their distinctive song. Most of the time they remain hidden in thick vegetation. In fact I’ve only seen this species twice before, and both times the birds were located by the loud song. The first time was a bird claiming its territory in May 2014 in a sand dune in Budle Bay, Northumberland and the second had probably only just arrived in the UK in April last year, when I found one singing in a garden at Selsey Bill in West Sussex from a small clump of ornamental pampas grass. In fact in the past 20 years Tony had only caught two or three, highlighting how lucky we were to catch this reclusive skulker.