BLAGDON LAKE BIRDS

Natalie's Diary


Natalie the Nathusius's Pipistrelle Pipistrellus nathusii © Nigel Milbourne, 2013

Saturday 11th May 2013;Despite the gale force winds during the day, the session was quite pleasant because the wind dropped to 5-10 mph at dusk and the temperature didn't drop below 7 Celsius. The evening was one of celebration as we caught the first ever ♀ Nathusius's Pipistrelle Pipistrellus nathusii at Blagdon Lake after a couple of years of trying. She was a good weight at 8.7 grams and apparently not pregnant, so Daniel decided that here was the chance to ring and fit a radio tag, weighing just 0.31 grams, that might help us work out where she is foraging and, more importantly, roosting.

Natalie the Nathusius's Pipistrelle Pipistrellus nathusii fur clipped between the shoulders © Nigel Milbourne, 2013

Natalie the Nathusius's Pipistrelle Pipistrellus nathusii with tag glued to back © Nigel Milbourne, 2013

Natalie the Nathusius's Pipistrelle Pipistrellus nathusii with radio tag fitted and fur replaced © Nigel Milbourne, 2013

Is she associating with other females? Will she lead us to a maternity colony (there are very few known maternity roosts in the UK)? Over the coming 14 days or so, about the life expectancy of the radio tag battery, we will do our best to find out as much as we can about her movements around the lake, provided the tag doesn't drop off (it will in due course anyway) or get removed by her prematurely. After release, she flew around in the woodland on Butcombe Bank before heading out across the bay and along the North Shore to Rugmoor Bank where Daniel picked her up feeding around the Indian Country pine belt and along the bank to Ash Tree before flying inland towards Grove Farm, Nempnett Thrubwell, where she appeared to roost. Both ♂ Nathusius's Pipistrelles were also ringed, and we noticed that one of them had a bad injury scab on its shoulder that appeared to be healing, thankfullly.

I have added some more information to the Nathusius's Pipistrelle species description including example spectrograms that I've recorded at the lake and some photos of identification features.

Sunday 12th May 2013; Daniel and I checked Natalie's radio tag was still working this afternoon and have more or less worked out where she is roosting by triangulation using two receivers. Daniel has always insisted a Jeep is the "ideal bat workers car"....

Daniel radio-tracking at Paradise, Blagdon Lake © Nigel Milbourne, 2013

Six bat workers gathered to radio-track Natalie this evening, and she appeared to wake up at around 2115 hrs and started moving around in her roost site. She came out to feed along the lee side of a lakeside hedge in a strong westerly wind (10-15 mph) at 2152 hrs. Some 15 minutes later she flew west along the North Shore and it was a further 15 minutes before we relocated her feeding at Butcombe Bank in the woodland near where we'd originally trapped her. We continued to monitor her behaviour in the woodland until midnight, when we left. The temperature was between 10-11 Celsius this evening and we only had a couple of showers. It's certainly worth mentioning the absolutley amazing clouds of chironomid midges over the lane in the lee of Indian Country pine belt as we made our way to Rugmoor Gate at the start of the evening. There's no shortage of bat food over there, that's for sure.

Monday 13th May 2013;Daniel checked to see if she had returned to her roost site at 0700 hrs, which she had. In the evening she emerged from the roost at 2139 hrs and flew east in a strong westerly wind (10-15 mph). We located her flying around over marginal vegetation (mainly reed canary grass) at Rugmoor Bay in the teeth of the blow at a height of 10-15 metres. Then, at 2230 hrs she made off along the North Shore again towards Butcombe Bank where we picked her up on the tracking equipment at 2250 hrs. However, by the time we'd driven around the lake she had flown back east to the farm where we located her again, probably roosting. The temperature was around 7-8 Celsius and rain set in. There was no more movement by 0130 hrs.

Tuesday 14th May 2013; Natalie was back in her roost this afternoon during a day of almost continual rain. I went down to start monitoring her behaviour at 2115 hrs and although she made a brief foray out in the drizzle, she went back to the farm and appeared to roost again, having apparently decided it was too cold and wet to forage. I left the site at 2300 hrs. Daniel stayed on for a while afterward. There was a breeze coming from east to north-east this evening and it was around 6 Celsius in the near-continual rain.

Wednesday 15th May 2013; I had to wait until 2155 hrs before there was any movement this evening, but by 2200 hrs Natalie was hunting on the east side of the hedge in front of me before quickly relocating to Rugmoor Bay and Indian Country pines to feed. She was continually on the wing there, mainly in the woodland, until flying back towards Rugmoor Gate at 2311 hrs and feeding out over the water at Peg's Point to Ash Tree until 2331 hrs when she flew in over the hedge and headed back to last nights roost at 2338 hrs. I left at midnight with her seemingly at roost. There was a westerly breeze until the sun went down and then it became calmer. However, the sky remained clear and the temperature dropped to around 5-6 Celsius by the time I left.

Thursday 16th May 2013; Daniel, Ken Anstey and I tracked Natalie on a calm but cold evening with the temperature already down to 7 Celsius when she emerged at 2150 hrs and 4 Celsius when she went back to roost at 2311 hrs. Rather predictably, Natalie flew over farmland to Rugmoor Bay where we thought she spent most of her time, but there is a bit of doubt about this now because with three of us available to track her, it is possible she spent most of the evening foraging on the south shore between Bell's Bush and Holt Copse. Just as Daniel arrived over there, she came back to Rugmoor Bay before cutting straight across the water to her roost. It was an early night for all of us.

Friday 17th May 2013; Finally, we had a calm, slightly milder night and Natalie decided to emerge a bit earlier at 2142 hrs. I thought she was going to go to Butcombe Bank when she headed west behind Ash Tree, but she decided to cross the lake from Ash Tree to Rainbow Point and started to feed along Burmah Road. Keith arrived and we were monitoring her from Peg's Point when Daniel arrived with some chips. Natalie headed back across the lake using the same route and appeared to be flying around her roost site at 2214 hrs. While we chatted and scoffed chips, she came back over us and appeared to head towards Rugmoor Bay. When we finished the supper, we coudn't get a squeak out of her! Daniel went to pick up four Glasgow students from the airport who are down for the weekend before heading out to Trinidad, and I left Keith at Peg's while I drove all around the area from Butcombe to Chew Valley Lake trying to relocate her. I had no luck, and when Daniel got back we suspected the transmitter may have come off. But eventually he got a very faint bleep from Dipland, Blagdon looking east so we drove all along the south shore but couldn't get another sound. Daniel took the students off to their campsite and Keith and I headed for Breach Hill and at 0040 hrs picked her up in the vicinity of Heron's Green at Chew Valley Lake. When we got there we thought she was over Moreton Bank so went to Herriott's to triangulate her position. From Herriott's we thought she was in the vicinity of Moreton and Stratford. A drive down Stratford Lane to the hide got us really close on occasions but then she headed back towards Heron's Green. We met Daniel there at around 0130 hrs and had a couple of close passes as she fed over the water in the bay. I left at 0230 hrs with her feeding well out over the lake but Daniel texted me later to say she had returned to her roost at Nempnett Thrubwell at 0300 hrs!

Saturday 18th May 2013; Speaking to Daniel during the afternoon, I learned that Natalie has given us the slip again. He said she came out of her regular roost again last night, just before dawn, and relocated into another farm close by, which has scuppered our roost check and filming this evening.

Keith and the Glasgow students are going to run some nets and a harp trap with lure this evening. We'll also be joined by the YAGWAGers. Depending on the wind, it's likely that we'll try trapping at Rugmoor for the first time. I'm hoping I might have recorded a Leisler's there during the week, so it'll be interesting to see if we manage to catch one. We'll also continue to track Natalie so it could be another long night.

Natalie started moving at 2149 hrs this evening and left her new roost site at 2152 hrs. By 2200 hrs she was at Rugmoor Bay, but a couple of minutes later her signal receded into the distance and we guessed she'd flown off to Chew Valley Lake. I drove over to Heron's Green and picked her up on the receiver foraging over the water right up against the causeway at 2350 hrs. Just before going home to bed at 0135 hrs, I checked again, and she seemed to be over at Moreton / Stratford, presumably making the most of the favourable feeding conditions.

Sunday 19th May 2013; Natalie was in her new alternative roost this afternoon when I checked with the radio tracking equipment. She came out at around 2150 hrs this evening and flew towards Rugmoor Bay at 2152 hrs. At 2207 hrs she was flying around at Top End before flying off east towards Chew Valley Lake at 2225 hrs. I turned on the tracking equipment again at 0004 hrs while we were trapping and she was back in the roost area. However, I couldn't pick her up just before I took the students back to their campsite, though Daniel texted later to say she was flying around nearby again at 0215 hrs.

Monday 20th May 2013; Natalie was on the move at her alternative roost site at 2205 hrs this evening, rather later than usual, came out shortly after. She appeared to fly across Rugmoor Bay and head across towards Burmah Road at 2208 hrs. However, it wasn't long before she started tracking towards Top End and flew off east towards Chew Valley Lake. I drove to Heron's Green shortly after and picked her up from there at 2230 hrs apparently over at Moreton/Stratford. I wonder what is attracting her to Chew that she can't find at Blagdon?

Tuesday 21st May 2013; I checked Natalie was still giving out a signal at lunchtime, so went down again in the evening to find out where she was going to forage in the calm conditions. At 2148 hrs she started moving at her alternative roost site at Rugmoor Farm, came out at 2150 hrs and flew around the farm buildings until 2205 hrs when she headed east over the fields without even going near Blagdon Lake. I set off for Chew as fast as I could and at 2214 hrs recorded her already flying at Moreton/Stratford.

Wednesday 22nd May 2013; This evening it was quite windy and cool and although the wind dropped at dusk, Natalie the Nathusius only came out briefly at 2154 hrs before returning to her Rugmoor Farm roost. At 2249 hrs a large cloud drifted across the bright moon and she was out like a rocket towards Rugmoor and Top End before heading east to Chew where I picked her up at Moreton Bank / Stratford from Herons Green at 2309 hrs.

Thursday 23rd May 2013; I went down to Rugmoor to check she was still giving out a signal and sure enough the steady 'beep beep' was coming from the direction of the farmhouse at 2111hrs. It was a bright night with a near full moon and some hazy cloud. So I settled down to wait to see if she changed her routine with the moderate north-westerly breeze blowing over the lake. I waited and waited and waited, but I just got a steady 'beep beep' coming back without any obvious signs of movement. At 2330 hrs I decided I was getting to the point of hypothermia and gave up. So, either she reasoned it was too cold to venture forth, or, her radio tag has finally dropped off in the roost. I hope it's the former because Daniel is hoping to film her coming out of the roost to see if there are other bats present. Although, I suppose that all the while the tag is giving off a signal, we still have a chance of finding the roost assuming it's dropped off inside.

Friday 24th May 2013; I met Daniel and Heidi at Rugmoor Gate and we waited for Natalie to come out of her roost, but the steady 'beep-beep' was unchanging until 2250 hrs when we decided that the radio tag had probably fallen off, as I suggested last night. We are hoping to be able to visit the farm and retrieve it tomorrow.

Saturday 25th May 2013; We didn't check on the apparently discarded radio tag today for various reasons.

Sunday 26th May 2013; Daniel, Heidi and I went to see if we could locate the radio tag at Rugmoor Farm this evening. We obtained permission to have a look around but, unfortunately, it has stopped giving out a signal and we couldn't find it. After Natalie's change of roost thwarting us last week, the failed tag has had the final say in her story - for now. However, having ringed her, we might yet meet up in the future.


Updated 28 September, 2013