Category: Biology

I’ve taken a few fairly close snaps of Wood Pigeons (Columba palumbus) and noticed that the pupils of their eyes do not seem to be perfectly round. Same with a few other birds, I assumed it was just an aberration, however, I wanted to be sure.

It didn’t take much web searching to discover that other people have noticed this too. Someone asked about it recently on the RSPB website and got a reply from Hein van Grouw, who is apparently Senior Curator, Bird Group at the Natural History Museum:

“Yes, wood pigeons seem to have non-circular pupils. The pupil, however, is circular but due to a spot of dark pigment in the iris the pupil seems to be non-circular. I have no idea what the reason (advantage) is for this. What I do know is that several other (tropical) species, mainly Fruit Doves, have it too.”

I must say though, it doesn’t look like pigmentation in the iris, it looks like a distortion of the edge of the pupil itself, at least in the photos I’ve taken. Oystercatchers have a pigment fleck too and you can tell what sex they are from this, apparently.

Wood Pigeons do seem to have really good eyesight regardless of the shape of their pupils, and perhaps partly because of them, they will veer off their flight path if they spot you walking below their course even through trees and can definitely see you from trees in the garden when you’re inside the house. That said, they will also completely ignore you if you don’t look at them and then take flight when they catch your eye. The eyes have it. (Hat tip to my Ladybird Farmer friend Simon for pointing that out).

Having invited the Waxwings to feast on our firethorn (pyracantha) berries, it turns out that a solitary Fieldfare (Turdus pilaris) has found the supply and a snow sanctuary in our front garden. Looking rather fed-up it has fluffed up its feathers against the cold and is rapidly working its way through the fruit of the firethorn.

Presumably, driven into more sheltered area because of the chills and snow out in the fields, those downy feathers are as fluffed as they can be.

Those nictating membranes (protective eyelids) are down much of the time in between snacks to protect its eyes from the snow flurries and the wind.

Fieldfares are true Thrushes along with Blackbirds, Song Thrush, Mistle Thrush, Redwing, and Ring Ouzel (the ones you’re quite likely to see in the British Isles, there are dozens of other Turdus species around the world. Turdus is Latin for Thrush as is the other half of the Fieldfare’s scientific binomial, pilaris. So its name is basically Thrush thrush. At least its compatriate the Redwing gets “flank” as the second half of its name Turdus iliacus, to indicate the prominent red markings on its flanks when it is perched with wings folded back.

Here’s my video about the Fieldfare.

A couple of people have asked me about the Peregrine photos I blogged a few days ago, specifically, what camera, lens, and settings I used to get the shots.

Well, first off I was standing at street level on the opposite side of the road to the church, it was a dull and overcast day. The female Peregrine was perched on a corner spire of the church tower about 34 metres above street level when I arrived, I used shutter priority to get a few shots of her and then tested aperture priority. When the male arrived and they mated I was in aperture priority mode and had to be quick to tweak settings as events unfolded.

Canon 6D, Sigma 150-600mm zoom. For what I consider the clearest and best shot I got, I had optical stabilisation switched on (to compensate for hand-held camera shake. I’d set aperture to f/11 to get some depth of field, centre-point focus and left the camera to choose the shutter speed (1/500s) and ISO 1600. I had also nudged the EV up at various stages and for this shot it was +3 to compensate for the camera reading the brightness of the sky, which would otherwise under-expose the birds.

The original photo was snapped in portrait orientation 3648 x 5472 pixels, cropped down to an approximately 1500 square for posting on social media, on Sciencebase it’s a watermarked 768 square. A few PaintShop tweaks included, bringing the blacks in, lightening shadows slightly, turning up the vibrancy a touch, and applying a relatively gentle unsharp mask.

Once again, I headed to our neighbouring village of Rampton armed with various lenses, tripod, camera etc, but there was barely a whisper of a murmuration this evening. A few small flocks and one half-decent one but quite a distance from the roost site that featured in my murmuration video on Sunday. There was definitely an Owl around but the Starlings seemed to favour the Cow Lane side of Rampton this evening. So, just a few scene-setting photos from today’s dusk chorus and one of mini-murmuration.

Here’s the video montage I did of the Starling Murmuration on Sunday in which there were probably 5000 birds in total. You can view it on Facebook or Youtube.

If you saw yesterday’s blog post, you will no doubt have some idea what a murmuration is – basically, a flock of European Starlings (Sturnus vulgaris) coalescing into a coherent flock just before they settle down to roost for the night. In case you missed it, here’s the video again:

There are two schools of thought as to why Starlings form these spectacular pre-roost murmurations. The first theory is the “safer together” hypothesis. Get yourself into a big, distracting flock and there’s more chance of confusing a predator, such as a Peregrine and less chance of being eaten before you go to bed. The second hypothesis is the “warmer together” idea wherein more birds roosting together will stay warmer through the night. The murmuration I videoed last night comprised several flocks with an estimated total of about 5000 birds, I reckon.

Anyway, last year there was a paper in Plos One that discussed a citizen science effort to try and find the most likely explanation for Starling murmurations. Anne E. Goodenough, Natasha Little, William S. Carpenter, and Adam G. Hart reported how flock movement and biomechanics have been the focus of research into murmurations, but efforts to find solid evidence of an explanation of this wonderful sight has been limited.

They collected data on size, duration, habitat, temperature and predators from members of the public, citizen scientists, who had observed more than 3000 murmurations. Sightings occurred in 23 countries but most were in the UK across lots of different habitats. Murmurations occurred mostly from October to early February with the average flock containing more than 30000 birds, but one murmuration reported as having 750,000 birds. The murmurations lasted on average just under half an hour, although the longest displays were at beginning and end of the season, which may be down to longer twilight time.

The team reports that birds of prey were sighted at almost one in three murmurations and that the size of the murmuration was bigger if raptors such as Harriers, Peregrines and Sparrowhawk were in the location. If a raptor was in close proximity to the flock, then the flock was more likely to end with all birds going down en masse to their roosting site. Temperature correlated negatively with murmuration duration.

“Our findings suggest that starling murmurations are primarily an anti-predator adaptation rather than being undertaken to attract larger numbers of individuals to increase roost warmth,” the team concludes. Earlier research by a different team had simulated a Starling flock to assess how confusing it might be to a raptor hoping to catch prey on the wing and supports the “safer together” hypothesis too.

This kind of self-organising flocking behaviour is common in shoals of banded killifish, among foraging ants, and in herds of migrating wildebeest, the team adds.

As regular readers will hopefully have realised by now, you don’t need to go too far from home to see astonishing natural wonders. Just a mile or so from our front door here in the Fen Edge north of Cambridge, for instance, I spotted a starling murmuration at dusk. It was happening over the main road out of the village of Rampton and the fields that flank it. So, having seen it in passing, Mrs Sciencebase and I headed there again today to get some video.

The sight and the sound were amazing, thousands of starlings swirling and whirling as they come into roost in the hedgerows just outside the village of Rampton as you head towards Willingham. There was also a Tawny Owl taunting some of the starlings along the hedgerow and a Little Owl calling from the field beyond; although neither of those feature in the video montage, I’m afraid.

In terms of why starlings flock like this, it’s thought that it throws Peregrines and other predators off the trail. Thousands of birds moving en masse do not present an easy target for a raptor that could otherwise dive on a single victim at over 200 miles per hour.

But, there could be other reasons for this flocking behaviour and as to the psychology of why humans see shapes and animals in the clouds of birds, well, that’s a wholly different story.

While seeing a murmuration on your own doorstep can be quite the spectacle there are even more alluring settings as these birds carry out their coordinated aerobatics in flocks with birds numbers tens of thousands if not hundreds of thousands the world over.