Category: Biology

I’ve talked about warblers before. Basically, the warblers are a non-scientific grouping of similar birds. In the UK, we often see and hear  a variety of warblers, mostly summer visitors, among them Blackcap, Cetti’s Warbler, Chiffchaff, Garden Warbler (Sylvia borin), Grasshopper Warbler, Great Reed Warbler (occasionally), Lesser Whitethroat, Reed Warbler, Sedge Warbler, Whitethroat, and Willow Warbler.

I headed to RSPB Fen Drayton Lakes nature reserve on a promise of Arctic Terns as a big influx had been reported on Tuesday, some 36, arriving in two waves, 29 and then 7, from Grafham Water. This is a huge number for one inland patch, especially in East Anglia.

More often, we’d have Common Terns and only a sporadic appearance of single figures Arctic. I had alerted the local birding community to a Sandwich Tern on 17th April 2024. A relative rarity that unusually stuck around for several days at the reserve. We also get Black Tern on these lakes.

Anyway, I saw just a few of the Arctic Terns on the water. However, a nice patch facing out over Ferry Lagoon fringed with some very noisy trees and bushes had Garden Warbler and Sedge Warbler calling noisily alongside Chiffchaff, Lesser Whitethroat, and Willow Warbler. There were several of each species. There were also two or three Cuckoo calling from far off trees. That aside, I got a shot of one of the Garden Warblers. I thought it was my first attempt at photographing this bird, but I discovered that I had photos of it in the warbler post from 2022.

At least 43 birds on sight or sound this morning:

Footnote: We do see Grasshopper Warblers (Groppers) locally, but I didn’t today. Dartford Warbler was seen a couple of summers ago, but a fairly rare sight. I’ve seen the rather rare Wood Warbler, but not in the UK, it was up the hill in Split, Croatia, back in 2017 before we drank all that dark ale on the way down and had catfish and chips for tea.

More about the British warblers on the BBC Countryfile site here.

Yesterday, I spotted a Sandwich Tern, Thalasseus sandvicensis, colloquially known as a Sarnie, patrolling the open river lock at Brownshill Staunch on the Great River Ouse. It flew back and forth over a stretch of about 200 metres for 20 minutes or so before heading off downstream.

The river cuts through the RSPB Ouse Fen nature reserve (I’d walked in from the Over end rather than Needingworth). The lock is currently open to allow flood water to run to the sea, although it’s not flowing as violently as it was about a month ago.

Anyway, I’ve seen several Common Terns fishing on this reserve and a Black Tern fly through one pre-covid summer. But, a Sandwich seemed unusual so I posted my spot to the local patch’s birding social media group when I first saw it. There was a flurry of interest and one member, Richard Thomas, keen to see the bird, headed to the Staunch. Unfortunately, for him the bird had moved on by the time he arrived, and I hadn’t checked back in on the group after my initial update to let them know. He dipped out. My bad.

I later spoke to Richard about the presence of the Sandwich Tern. I had assumed it wasn’t a so-called mega rarity, but still its presence was rather unusual. He told me he thinks they’re almost annual in this area despite their being so obviously coastal feeders and breeders.

“Sandwich Terns are just about annual locally – I’ve seen them on six occasions in 20 years and missed them more times than that,” Richard told me. “They are an absolute pain in the neck because they rarely stay more than a few minutes. I’ve been lucky on four occasions with “fly throughs” (including a flock of seven at the Brownshill Staunch).” He added that they’re annual at Grafham Water reservoir, which isn’t far from here either and a nice birding spot, but again, he says, they were almost invariably fly throughs.

There was a subsequent flurry of activity in the social media group, my having alerted the birders to the presence of the species, and it was quickly tracked down to yet another patch of old gravel pits turned nature reserve, RSPB Fen Drayton. Several birders were excited to know it was there and surprised that it had roosted rather than flying through.

The River Great Ouse empties into The Wash on the north Norfolk coast. It’s worth noting that Brownshill Staunch, which lies on the Greenwich Meridian, is the last stretch of the river that still feels the effects of the tide. In recent weeks, my fellow togger friend Andy Hoy saw a seal sunning itself on the riverbank at this point. It had presumably swum upstream from the coast. Seals are not uncommon on the river, although they’re usually seen further downstream. In the summer of 2023, a female dolphin and two offspring were seen on this stretch of river too.

Richard has the last word in adding that one good tern deserves another, he suggests that Caspian Tern or Roseate Tern would be firsts for the patch should they turn up…

Latest intel on the Sarnie is that it’s feeding on the river near Ferry Lagoon at RSPB Fen Drayton 18h00 on the 18th April. On the 17th it roosted on the islands in the Lagoon. The bird was still being seen on 20th April. Interesting that quite rare for this species to stay in Cambridgeshire this long. Some birders said not known it before, others pointed out that one may have over-wintered at Grafham Water in 1987.

Having spent a couple of evenings watching Starling murmurations with hundreds of thousands of birds, it was time to seek out some Aves in smaller numbers. I had a quick look in at RSPB Ouse Fen (Earith) as it was bright and sunny on Saturday morning. I was hoping to that there would be a chance that the Cranes would be showing. They weren’t but there was a Great White Egret, as ever, and a Chinese Water Deer, I had only fleeting, distant views of a solitary Marsh Harrier. I headed out to Chain Corner to check on the Whooper Swans, a few on the water and one that flew right over me.

Next on to a patch of flooded farmland, often used for fen skating historically, it had lots of waterfowl, but no Glossy Ibis there this year, despite their having bred not far from here in 2023. Then on to RSPB Berry Fen, which is just a short hop further up the road. Chiffchaff calling, lots of Widgeon whistling but no Black-tailed Godwit, there were several hundred earlier last week, apparently.

There was also a distant piping Redshank and the Merlin app picked up the sound of a Green-winged Teal (it’s perhaps the same American vagrant we’ve seen here over the last two or three years; previously, there has also been a Blue-winged Teal). There had also been Dunlin and similar species there but I couldn’t see them. There was a Sparrowhawk, known affectionately as a Sprawk to birders, that flew right over me and away with its familiar flap-flap-glide flight pattern.

Further round, the flood, a group of Greylag Geese hanging out with some Russian visitors – three White-fronted Geese. This species, Anser albifrons, might better be known as “white-faced” as you can see from the photos. But as is often the wont of naturalists names sometimes don’t quite match the species description.

According to the BTO website: Two races of White-fronted Goose occur in the UK. A. albifrons (the European WfG) breeds in western Russia and is usually about 1000 to 2000 of them are found in the south and east of England in the winter. A. flavirostris breeds in western Greenland (the Greenland WfG) and about 10000-12000 of this subspecies usually spend the winter in the north and west of Britain and Ireland.

UPDATE: I mentioned the murmurations to a choir friend, Sara, and bumped into her and her husband on the Fen. I warned them that, because it was very windy, we might not get such good murmurations as I’d mentioned before. But amazingly, as dusk rolled on, even though it wasn’t a bright sunset, we got some wonderful activity from a staggering half a million Starlings.

I chunk estimated numbers from my photos and the video at perhaps 400,000. However, I then fed some photos and video stills to Google Gemini AI and asked it to process, analyse, and count the birds. Gemini estimated the size of the flock in my video from a still capture as being 500,000. There were many more birds outside the video frame, so I suspect on this evening there were between 550,000 and 650,000 birds murmurating. ChatGPT got similar numbers from my photos. Microsoft Copilot simply told me the images were of murmurations and said it was too difficult to count the number of birds.

The main activity was very much over the reedbeds among which we stood rather than being half a mile away as occurred on my previous two visits.  This made it hard to get the full murmuration in the camera frame at the level of zoom I had with me. So, the above video was done on my phone as a record.

The birds would whoosh over out heads at about 50 metres altitude. I warned the people around me not to look up with their mouths open and within a few minutes, my choir friend had undergone a full birding initiation with three deposits from above in quick succession. Amazing that I didn’t get splashed as I was standing only a metre or two away from her.

Anyway, the birds gathered in a very dense flock at about 17h50 and bedded down into the vast reedbed in front of the entrance to the reserve. There were undulations for a good ten minutes as it got darker and darker. At one point, a Merlin was reported to have caught one Starling on the wing. The other 199,999 were fine and had roosted down among the reeds by the time we departed.

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At the end of February, I got wind of there being very large numbers of Common Starling murmurating at a local nature reserve – RSPB Ouse Fen (Earith). I got a few photos on an evening visit. There were probably half a million birds, it was quite astonishing. I based my estimate on counts I’ve done of photographs of smaller flocks and extrapolating to the huge patches of sky that were covered with birds on the evening.

I got some nice photos at sunset but my phone video was very smeary and low-res. So, a second visit was essential. Unfortunately, rumour had it that the numbers the next night were smaller, that some of the birds had moved to roosting over the Over side of RSPB Ouse Fen…nevertheless, Mrs Sciencebase and myself headed over to Earith on 3rd March.

It was a much better evening and definitey fewer Starlings, but still many tens of thousands. This time I got some decent video footage of the murmurations.

We also ticked three Short-eared Owls, half a dozen Chinese Water Deer, heard numerous Cetti’s Warbler and saw just one, saw Great White Egret and Grey Heron, heard a couple of Bearded Reedling, and heard one or two booming Bitterns, lots of Geese, Cormorants, Reed Bunting, Widgeon calling, Little Grebe, Water Rail etc. The Cranes that had been displaying south of the car park on the gravel works land flew in to roost about a quarter of a mile in front of us as we watched the starling murmurations. It was a wonderful evening of nature watching.

I played my video to the Merlin app, although we all knew what birds we could hear, but it came back with Coot, Greylag Goose, Canada Goose, Cetti’s Warbler, Ring-necked Pheasant. It didn’t pick up Wigeon, Little Grebe, Reed Bunting, Bearded Reedling, which we had heard.

I opened up one of my stills with a huge flock across it and enlarged it on my laptop screen. I drew a square around a patch that I estimated had 100 birds in it. Double-checked and adjusted the size of the square to make sure it was very close to 100. I measured the square in pixels and then worked out how many such squares would fill the area of the photo filled with birds. It came to about 75000 birds. This assumes average density across the photo. There were probably areas outside the area of the photo that would be around 25000 birds. So, the biggest flock would be around 100000, there were probably about half the same number of birds in the air elsewhere. The previous evening of murmurations I’d have said there were 5-6 such flocks, so guesstimating at least half a million birds going to roost on this patch of the reserve.