The Warbler Factory
By Graeme Lyons
Senior Ecologist
Butcherlands. The most exciting, unpredictable and constantly changing Common Bird Census (CBC) I have ever done. This is the eighth year I have carried out the four visit CBC there and it's amazing how much it's changed. Eighteen years ago this was all arable on Wealden Clay and was fenced and left to be restored to something more natural with pulse grazing by cattle currently pretty much the only management. No planting occurred and there are at least 30,000 oaks out there alone. Before looking at some of the detail though I am gonna cut right to the chase and tell you about what happened yesterday morning. First though a recap from my first visit on the 3rd April 2019. I had a Hawfinch fly over (my first since the previous winter's influx) and then surprisingly a male Dartford Warbler called repeatedly from a bramble bush. Not all that unusual to pick them up in bramble scrub away from the heaths outside of the breeding season (I've seen them in Sheepcote Valley on the edge of Brighton for example).
Scrub at Butcherlands
Yesterday morning, the warblers were in full song. Whitethroats were EVERYWHERE. I recorded 44 singing males across the site. So when I got to the exact same area and heard Dartford Warbler calling again, I was pretty shocked. "It's holding territory!". I bungled the video last time so I got a quick video of it calling and you can see it fly from the bush to the left.
I thought I really should try and hear it singing, so I headed a few bushes away and crouched down out of view. It didn't work and the bird came towards me, scolding me from just a few metres away. I grabbed another video as it did so and it started singing a tiny bit. However what happened next was incredible. A female popped up out of the same bush! "THEY'RE HOLDING TERRITORY!". Some context here, there isn't any heather at Butcherlands, there is however hectares of low bramble scrub. This part of the site is on the edge of a sea of undulating bramble. It's also south west facing with a slightly sandy soil (more Common Bent/Cat's-ear than Heather). So it's hot, dry and with a structural component close to heather/low gorse. I never thought that this would be a thing at Butcherlands but these birds are much less fussy abroad. It may well be that this structural type and temperature envelope is rarely provided outside of the heaths in the UK.
Has anyone else encountered this in the UK before?
Yesterday morning my brain was totally fried from all the warblers. After this encounter I was doubting every Whitethroat that called, after all, if one pair of Darties could nest there, why not more? I really doubt I would have picked them up with so many Whitethroats there if I hadn't found the male three weeks ago. So many questions. So exciting!
I actually recorded over 75 singing warblers yesterday! My rule for difficult species pairs is this: if you're not sure, it's the commoner one. Think I'll call that 'Lyons' Razor'. It certainly came in handy with a few Blackcaps today. A Blackcap AND a Garden Warbler taking turns to sing from the same willow nearly made me lose my mind though.
Whitethroat - 44
Chiffchaff - 11
Garden Warbler - 8
Blackckap - 8
Lesser Whitethroat - 4
Dartford Warbler - 1
That's 76 warblers in all. Plus ten Nightingales and a Cuckoo.