The mystery of the green-winged teal at Eoligarry flood

Yesterday a drake green-winged teal was found at Eoligarry, on the flood created by heavy rain over the past two days. It apparently arrived as part of an influx of about 10 teal, more than we had previously seen at Eoligarry. We had a quick look at the bird in fading light yesterday evening and saw that it had quite dull vertical white stripes, which we put down to either the poor evening light or the fact that the bird was perhaps not yet in full plumage having just moulted out of eclipse. 

On returning for another look this morning, we were surprised to see that it actually now had two quite bright vertical white stripes. While we were watching, it disappeared into the vegetation and less than a minute later we spotted a green-winged teal some 50m to the right on the edge of the pool, without us seeing it fly or swim there across open water. Surely that couldn't be the same bird? Where there two green-winged teal present?

Then Ray pointed out another bird which was still moulting, with plenty of brown feathers in amongst the fresh grey flanks, but with a white mark on both sides at the top of where the white vertical bar should be. The rest of the bar was obscured by brown feathers. Was this another drake green-winged teal and if so just how many were there? One thing for sure, there was at least one certain drake Eurasian teal in the group.

The viewing conditions were difficult, the teal were at a distance of about 100m, in and out of the flooded vegetation, it was very windy, misty and dull with some heavy drizzly showers which soaked the optics. Also the birds were just coming out of moult, so it was difficult to be certain if the markings we were seeing, or not seeing, were real or just aberrations of moult. In the end we decided that we could only be certain that there was one bird present because we didn't see the dull and bright birds together.

However, the following day we received a message on the Barra birders WhatsApp group that there were two, probably three green-winged teal on the flood. We decided to head back later for another look, but unfortunately the teal were flushed by a buzzard and flew south before we arrived and were not seen again. Over the next few days the flood subsided to more normal marshy field levels and we had no further sightings of any teal.

I had taken several videos of the teal on my phone and through the telescope, all of which are shaky and of poor quality and don't really prove anything, especially since I had been following around the well marked bird rather than trying to find other birds. 

Most intriguing to me is how many of the females were green-winged teal? The identification of females is very difficult at the best of times and probably impossible in the kind of conditions that we had to contend with here.

However, even before the possibility of there being more than one drake was raised, I had noticed in the field that some of the females looked darker than I would normally expect and some had a well-marked  head pattern of dark crown, pale supercilium and dark eye-stripe. This is a feature, though not conclusive, of female green-winged teal as described by Hugh Harrop in a short paper in British Birds 112, January 2019: 35-43(opens in a new window). 

Apparently the key feature to look out for when attempting to identify female green-winged teal is the pattern on the outermost tertial, something which I was not aware of at the time and which try as I might, I can't see in my videos. 

However, even making allowances for the poor quality video, the female in this photo looks dark  

While a closer look at this photo shows just how dark the top female is and perhaps even shows a very pale looking last tertial which is exactly what female green-winged teal should have, when compared to Eurasian teal which has a dark looking last tertial, due to the difference in pattern on the feather. It's impossible to be certain though from my videos and photos. It's just a pity that I wasn't aware of the differences in tertial pattern when I was watching the birds.

So I'll never know for sure how many, if any, of the females on Eoligarry flood were green-winged teal but it seems likely that if three drake green-winged teal arrive in a flock of 10 new arrivals on an Outer Hebridean Island in October, then there is a good chance that there will also be a female or two with them.