17th August

If yesterday was a day to forget then today barely merits a mention, even the Manx Shearwaters didn't make it to double figures. Four Balearic Shearwaters and 2 Bonxies made up the mornings sea-watch totals. The land was almost deathly quiet with a pair of Willow Warblers and four Wheatears making up the entire grounded passerine count for the day at the Bill. Ferrybridge held little to inspire with the usual selection of waders accompanied by the 2 long-staying Little Gulls.

The pick of the day's lepidoptera were a noticeable hatch/arrival of Clouded Yellows that included at least 11 at the Bill.

We've occasionally made reference on the blog to the acoustic bat monitoring - primarily to inform research into the migration of Nathusius' Pipistrelle - being undertaken at the Obs. Sadly, beyond managing the hardware, we still haven't found time to get involved in the analysis of the recordings obtained so we're fortunate that Adrian Bicker, who instigated this project in the first instance, is still on board to undertake this work. We were very excited to hear back from Adrian this week that amongst our latest batch of recordings he'd identified calls of the rare Kuhl's Pipistrelle from the evening of 3rd May (at 21:16; sunset on this date was at 20:19) when the bat detector was situated at the top of the Obs lighthouse tower:

Adrian comments that: Nathusius' Pipistrelles produce similar calls to Kuhl’s, with a strong, near-vertical FM “chirp” but such calls would be at or just above 40kHz. These calls are much lower – just like the 1,900 Kuhl’s calls collected from the Brittany coast as part of my spring Nathusius' Pipistrelle migration survey. Many of the Brittany calls had the diagnostic low, slow “ChowChowChow” (or “ChowChow”) social calls which confirm Kuhl’s. The spectrograms shows the calls.  The vertical axis is frequency (grid lines at 40kHz and 36kHz). The strong echoes show that the bat flew over the observatory’s flat roof; the 27ms delay indicates that the echo travelled 9m further than the call!