Biology – Page 6 – David Bradley

Waxing lyrical in Bohemia

I was chuffed to bits to catch up with these delightful winter visitors not 20 minutes from home. There were just 4 of the 20+ that had been showing an hour or so before I arrived #waxwings.

Waxwing feeding on Rowan berries

There are ~~two~~ four flocks local to Cambridge, possibly more. Their preference is for Rowan berries so anywhere you see those, you might see Waxwings. B&Q car parks, bus stations, hospitals etc etc. See my previous post on this specific topic.

Waxwing feeding on Rowan berries

Given that it seems we are definitely seeing an irruption winter with sightings all across the UK and some relatively large flocks showing up, chances of catching sight of them are fairly high.

Waxwing feeding on Rowan berries

They tend to gather at the tops of tall trees, occasionally calling “trrrreeee, trrrreee, trreeeee” and then dropping down to feast on the berries. They can quickly strip even the most fecund of Rowan trees before moving on, leaving little for the resident blackbirds or any incoming Fieldfares or Redwings (also winter visitors, but thrushes). In the photo below you can perhaps see that the bird’s tongue appears to be barbed. If it is, then that is presumably an adaptation for being able to grab these berries so efficiently. Not how many “ends” on those twigs are missing a berry!

Waxwing feeding on Rowan berries

I hadn’t had a chance to see any since early in 2017, which i think was the previous irruption year.

Waxwing feeding on Rowan berries

Twitching and dipping out a Waxwing

Word on the birding street is that this winter is going to be bright for lovers of one of our winter visitors – the Waxwing, Bombycilla garrulus. This bird is more formally known as the Bohemian Waxwing as opposed to the American bird, the Cedar Waxwing, B. cedrorum. There were quite a few sightings early on in Scotland as these birds that spend the summer much further north than that began to head south.

Sightings in England have been on the rise as of late November, early December 2023. The nearest relatively large flock for me is in Norwich. Too far for me to make that trip just for the birds. However, word went out that a solitary bird was in trees next to the recreation ground in a village just up the road, Stretham. Usually, the flocks tend to congregate in places with large plantings of berry-laden trees, like rowans, such as supermarket car parks, transport hubs and service stations, as I’ve mentioned before.

A Meadow Pipit in the Spring on Anglesey

It wasn’t such a long twitch to head to Stretham from here to have a look for the bird. I scanned every tree in the vicinity, took a long walk around the village scouting out rowans and cherry trees to no avail.

I didn’t see the Waxwing. I dipped out, as birders say (check out my tongue-in-beak birding glossary for definitions of such terms).

However, I had the Merlin app running on my phone all the while for audio birding, you might say. There was the off-chance that it would pick up the Waxwing calling and I might be able to find it. But, unfortunately, I didn’t. I heard various birds as did the app: Carrion Crow, Collared Dove, Common Pheasant, Common Starling, Eurasian Blue Tit, Eurasian Jackdaw, Eurasian Skylark, European Greenfinch, European Robin, Great Tit, House Sparrow, Long-tailed Tit, Meadow Pipit, Redwing, Rook. All of these birds are quite likely in the area.

The app, however, also claimed to have heard a Hooded Crow, but they are rather rare this far south and I haven’t seen one mentioned in Cambridgeshire for several years. So, I suspect it was a misidentified Carrion Crow call.

Where is the best place to see Waxwings?

Where is the best place to catch sight of one of the most beautiful of winter visitors, when it comes to birds? The Bohemian Waxwing, Bombycilla garrulus.

Waxwing closeup — At one point early in 2024, there were 30+ Waxwing feeding on rowan berries next to a local railway station

You might imagine it would be some delightful hill or vale, a nature reserve, or perhaps a remote woodland. Well, that’s not the case. This distinctive species heads south to the UK when it gets too cold for it in northern parts and when the supply of berries on which it feeds dries up. As of December 2023, it seems like we are in the middle of an irruption of these birds with relatively large numbers turning up in all sorts of places right across the UK.

Best places to see them are where there are lots of trees with lots of berries, rowans and other species. They seem to like to observe their “feeding station” from on high, so if there are other taller trees, like poplar and ash overlooking the rowans, all the better, but tall lamp posts might do just as well as a perch. So, where might those places be? Well, town planners and architects like to put these attractive trees on trading estates, retail parks, next to bus stops and bus stations, science parks, road junctions, brickyards, city parks, pub beer gardens, service stations, school playing fields, supermarket car parks and the like! If you’re very lucky and have a decent feast for them, you might even get them in your garden.

Waxwing feeding on berries in a tree, Newcastle — Waxwing feeding on berries in a tree next to a bus stop near Newcastle-upon-Tyne on a grey, drizzly day. This was my first chance to photograph the species.

Just scanning the Birdguides page for recent sightings during this wonderful 23/24 winter irruption of Boho Wx, here are some of the sites:

Tram stop, Didsbury
Quarry, Flintshire
Churchyard, Aldermaston
Cemetery, Romsey
Car park, Garforth
Road junction, Wharfedale
Canal towpath, Aylstone
Road junction, Skipton
Cobbler’s Walk, Bushy Park, London
Car park, Rodborough
Road junction, Leuchars
Road junction, Colchester
Road junction, East Hunsbury
Community centre, Watford
Pub, Tonbridge
Pub, Chafford Hundred
Retail park, Middlesborough
Road bypass, Nescliffe Hill
High School, Earlston
Roundabout, Maresfield
Caravan park, Fife
Airbase, Brize Norton
Road junction, Waltham Cross
Historical building, Rodborough
Car showroom, Elgin
Cricket club, Long Hanborough
Shop, Hailsham
Station car park, Merstham
Roundabout, Thringstone
Nature reserve car park, Hesketh

A bird’s eye view

Birds have incredible visual systems. This is especially true of the birds of prey, the raptors, which includes the hawks, falcons, eagles, buzzards, harriers, owls, and others.

Red Kite staring at me from its perch atop a conifer. Bird to camera distance about 50 metres — Red Kite staring at me from its perch atop a conifer

Unlike many other types of birds, the raptors have binocular vision, their eyes face forward, like ours, which means they have a 3D view of the world ahead of them. This allows them to pinpoint prey incredibly well even from great distances as is the case with the Peregrine Falcon. That species, and others, also have two fovea, the most sensitive regions of the light-sensitive retinas at the back of their eyes. They use one for homing in on prey from a distance but switch to other for greater precision as they get closer to their prey. There are many other adaptations in raptor vision.

I was photographing a Red Kite recently when I noticed one such adaptation that I hadn’t seen before. The bird was perched atop a conifer and I approached slowly to get a relatively close view without disturbing it. It ignored me to begin with and I got a nice photo of it staring out of the surrounding farmland.

Red Kite taking flight — Red Kite takes flight

I took a burst of photos and in one when the bird had turned to stare at me on the ground I could see that half of its face was in sunlight, the other half in the shadow of its beak. If you look closely at my photo, you can see that the pupil of its right eye, the one in the sunlight, is smaller, while the one in shadow is larger. The bird is adjusting pupil size independently depending on how much light is reaching the eyes. This is not something that we humans can do. If one eye is in the light and the other the dark, both pupils will still be the same size.

Closeup of Red Kite showing pupils differently dilated — Closeup of Red Kite showing pupils dilated to a different degree

This is a remarkable adaptation – independent pupil control or pupil asymmetry, also known as anisocoria. It allows many birds to finely adjust the size and shape of each pupil. Anisocoria is a general term for having pupils of different size. Famously, musician David Bowie had a fully dilated left eye pupil having sustained an injury to that eye as a youth. My late mother had a viral infection when she was middle-aged that also left her with an unresponsive, and almost fully dilated pupil in one eye. Apparently, one in five people have anisocoria, but in raptors its a positive trait rather than a problem.

This independent pupil control serves various purposes. One key advantage is the regulation of light entering each eye independently, optimizing vision in different lighting conditions. The ability to control each pupil independently aids in maintaining a stable image on the retina, crucial during activities like flying or hunting, where motion is involved.

From an optics point of view, photographers know that a larger aperture on their camera, which is equivalent to the pupil being more dilated in the eye means more light can reach the sensor or film, analogously to reaching the retina. But, this comes at the cost of a shorter depth of field. So, if the camera or eye is focused on a subject, then much of what is closer or further from this focus point will be out of focus or blurred. Make the aperture smaller and there is less light entering camera or eye, but the depth of field is greater.

Another adaptation that many more bird species have is a third eyelid. This is known technically as a nictitating membrane, it lies beneath the upper and lower eyelid and can sweep across the eye independently of the outer two lids. It has usually transparenty or semi-transparent. It has various purposes, fundamentally it acts as a protective layer that closes over the eye when a bird is feeding chicks or killing prey. It can also protect the eye from glare or allow a diving bird to enter the water without being temporarily blind but without the risk of damage from the impact or, again, impact with its prey or objects hidden from view under the water.

One of my Red Kites (there were a dozen around the patch on the day) obliged with a quick view of its nictitating membranes among the burst of photos I took.

Nictitating membranes, Red Kite — In this rather “painterly” zoom and crop you can hopefully discern the Red Kite’s nictitating membranes

I have previously talked about the pupils of another type of bird, the Wood Pigeon, Columba palumbus. In this species, the shape of the pupil seems unusually asymmetric, but this is an illusion due to the presence of a portion of pigment in the eye adjacent to the bird’s pupils.

Birders versus Toggers

Broadly speaking, birders are avian enthusiasts, people interesting in seeing birds. Sometimes birders are twitchers, they like to see a bird so they can “tick” that species off a list, often it involves travelling far from their patch to see a species new to them. Twitchers are often not birders, they’re more akin to collectors, but aren’t necessarily interested in the birds per se. Then there are people with cameras who are also birders, twitchers, or both. Birders and twitchers often refer to these birding photographers as toggers, it’s a rather derogatory word.

Now, if a bird of interest shows up on a patch, the Short-eared Owl for instance, several of which we see out on the Cambridgeshire Fens in winter, then birders, twitchers, and toggers, and every permutation thereof, will generally hear about it and head for the patch, to get a look at the bird through their binoculars, and scopes, to tick their list, and to get that perfect photo.

Often the groups overlap, especially on a small patch, or where there’s a good vantage point. There’s often some sneering among the snobbish members of whichever group who see their particular hobby as being the more righteous.

None of these hobbies have any real claim to righteousness, all of us who indulge are impinging in some way on the wild patch that the birds have chosen to inhabit however temporarily. The presence of humans may well be disrupting the birds’ normal behaviour. So, it’s interesting to hear different people complain about the presence of members of the other groups of enthusiasts if they perceive the activity of the others as being more detrimental to the birds and the environment than their own activity. There is an argument to say that people should leave the wild to the wildlife.

One comment I read on a birding group recently was lamenting the number of people who had turned up at one of our local Cambridgeshire Fens to see and photograph the aforementioned Short-eared Owls (Shorties or SEOs). They said, apparently in all seriousness while lugging their scope up and down the Fen, that all these toggers running around were agitating the birds and making the place like a theme park. They asked the question: “How many photos of one bird do they need?”

Well, without getting into the art and craft of bird photography and why you might need to take more than one photograph, I wonder how they perceive their own position in terms of simply looking at the bird…surely the question might be asked of them “How many times do you need to look at one bird?”

Anyway, I personally feel that I’m just a bird enthusiast with a camera. I don’t think of myself as a proper birder, I don’t know enough. I’m not a twitcher, I’ve rarely “twitched” a species (successfully the European Roller that turned up not far from here, the European Bee-eaters in Norfolk when we were visiting, and the Black-browed Albatross that we failed to see at Bempton Cliffs). And, what photographer would call themselves a “togger”?

Enthusiasts and hobbyists of all creeds need to get over themselves, get over their self-righteousness. They need to not start this kind of argument on a public forum for the sake of assuaging what is probably their own guilt about their hobby and whether it is ethical to impinge on the wild in the first place.

We should all take more care to minimise any detrimental impact we have on wildlife and the environment. And, we should all take care to minimise our snarky comments, which can lead to bad feeling between different factions within a wider community that are to all intents and purposes seeking the same positive satisfaction from their interaction with nature.

Invasive species in the UK

Invasive species, a term referring to non-native species introduced to new environments, often establish self-sustaining populations with negative impacts on local ecosystems, economies, or human health.

These invaders, encompassing plants, animals, fungi, or microorganisms (refer to the foot of this article for examples), typically arrive due to human activities such as trade, travel, or intentional release. In rare cases, invasive species might reach the UK through natural avenues, such as animal migration or wind dispersal. Climate change exacerbates the situation, creating new ecological niches due to shifts in temperature and persistent weather changes. Alterations in landscape, urbanization, and habitat loss add pressure to natural ecosystems while simultaneously creating new opportunities for invasive species.

In the context of the United Kingdom, invasive species present significant challenges for various reasons:

Ecological impact: Invasive species can outcompete native species for resources including food, water, and habitat. They may have no natural predators in their new environment, allowing their populations to grow unchecked. This can lead to the decline or extinction of native species, disrupting the balance of the ecosystem.

Biodiversity loss: The displacement of native species by invasive ones can lead to a loss of biodiversity. Native species are often adapted to specific ecological niches, and the introduction of invasive species can disrupt these relationships, leading to a reduction in overall biodiversity.

Human health and safety: Some invasive species can pose risks to human health. For instance, certain plants may be toxic, and some animals may carry diseases that can affect humans. Additionally, invasive species can create safety hazards; for example, certain plants or animals might be harmful if they interfere with buildings, bridges, transportation systems.

Economic consequences: Invasive species can have economic impacts on agriculture, fisheries, and forestry. For example, invasive plants can reduce crop yields, while invasive animals may damage crops or compete with native species for resources. Invasive species can also impact infrastructure, such as clogging waterways or damaging buildings.

Increased management costs: Controlling and managing invasive species can be expensive. Governments, communities, and individuals may need to invest significant resources in efforts to control or eradicate invasive species and mitigate their impacts.

In the UK, various organizations and initiatives actively monitor and address the issue of invasive species. This global concern necessitates efforts to prevent introductions, manage existing populations, and control their impacts, preserving biodiversity, ecosystem health, and human well-being.

It’s crucial to note that some invasive species in the UK have been present for centuries, becoming integrated into local ecosystems. For example, the sycamore, recently in the news having been vandalistically felled at Sycamore Gap on Hadrian’s Wall in Northumberland, had long been part of the landscape but sycamores arrived with the Romans. Distinguishing between long-established non-native species and recent arrivals is crucial for effective management.

Despite confounding factors, certain invasive species contribute to ecosystem services, such as soil stabilization, water filtration, and habitat provision. Invasive crayfish used as food in mainland Europe have established themselves in the lakes of France and Spain and this in turn has allowed ostensibly African and Mediterranean birds such as the Great White Egret and Glossy Ibis to spread further north. It was only a short hop for them across the English Channel to the UK where they are no beginning to establish themselves, without apparent harm to native species or ecosystems it seems.

Indeed, some invasive species may enhance overall biodiversity by providing new habitats or food sources for native species, fostering a more diverse and resilient ecosystem. Additionally, there’s potential for utilizing invasive species in agriculture, forestry, and horticulture.

Examples of invasive species present in the UK

Plants:

American Skunk Cabbage (Lysichiton americanus)
Australian Swamp Stonecrop (Crassula helmsii)
Chilean Rhubarb (Gunnera tinctoria)
Cotoneaster species (Cotoneaster sp.)
Cotula Silverweed (Argentina anserina)
Curly Waterweed (Lagarosiphon major)
Floating Pennywort (Hydrocotyle ranunculoides)
Floating Water Plantain (Luronium natans)
Giant Hogweed (Heracleum mantegazzianum)
Himalayan Balsam (Impatiens glandulifera)
Hottentot Fig (Carpobrotus edulis)
Japanese Knotweed (Fallopia japonica)
Japanese Rose (Rosa rugosa)
Parrot’s Feather (Myriophyllum aquaticum)
Rhododendron (Rhododendron ponticum)
Small-Flowered Water-Weed (Elodea nuttallii)
Spanish Bluebell (Hyacinthoides hispanica)
Water Fern (Azolla filiculoides)
Water Primrose (Ludwigia grandiflora)
Winter Heliotrope (Petasites fragrans)
Yellow Azolla (Azolla caroliniana)

Invertebrates:

Asian Hornet (Vespa velutina nigrithorax)
Asian Tiger Mosquito (Aedes albopictus)
Box-tree Moth (Cydalima perspectalis)
Chinese Mitten Crab (Eriocheir sinensis)
Emerald Ash Borer (Agrilus planipennis)
Harlequin Ladybird (Harmonia axyridis)
Harlequin Shrimp (Hymenocera picta)
Horse Chestnut Leaf Miner (Cameraria ohridella)
New Zealand Flatworm (Arthurdendyus triangulatus)
New Zealand Mud Snail (Potamopyrgus antipodarum)
Oak Pinhole Borer beetle (Platypus cylindrus)
Oak Processionary Moth (Thaumetopea processionea)
Quagga Mussel (Dreissena rostriformis bugensis)
Red Swamp Crayfish (Procambarus clarkii)
Rosemary Beetle (Chrysolina americana)
Signal Crayfish (Pacifastacus leniusculus)
Spanish Slug (Arion vulgaris)
White-Legged Shrimp (Litopenaeus vannamei)
Zebra Mussel (Dreissena polymorpha)

Vertebrates:

American Bullfrog (Lithobates catesbeianus)
American Mink (Neovison vison)
Black Rat (Rattus rattus)
Canada Goose (Branta canadensis)
Chinese Water Deer (Hydropotes inermis)
Egyptian Goose (Alopochen aegyptiaca)
Grey Squirrel (Sciurus carolinensis)
Muntjac Deer (Muntiacus reevesi)
Parakeet sp.
Pumpkinseed Sunfish (Lepomis gibbosus)
Raccoon (Procyon lotor)
Red-Eared Slider (Trachemys scripta elegans)
Ruddy Duck (Oxyura jamaicensis)
Sika Deer (Cervus nippon)
The Red-Eared Slider terrapin (Trachemys scripta elegans)
Topmouth Gudgeon (Pseudorasbora parva)
Wallaby (Macropus sp.)
Yellow-Bellied Slider terrapin (Trachemys scripta scripta)

Fungi/Microbes:

Chalara Ash Dieback (Hymenoscyphus fraxineus)
Dutch Elm Disease (Ophiostoma ulmi)
Horse Chestnut Bleeding Canker (Pseudomonas syringae pv. aesculi)
Phytophthora Ramorum (Phytophthora ramorum)
Sudden Oak Death (Phytophthora sp.)

The Winter Moth – Operophtera brumata

This unassuming little moth has a suitably unassuming little name. It is known as the Winter Moth. It is one of the geometers, or what is referred to as inchworms in North America, because the larvae seem to measure out the earth as they move inch by inch.

The Winter Moth is not to be confused with the November nor the December Moth. It flies at the opposite end of the season to most other moths – October to December and sometimes into January and even February. It is unlikely to ever cross paths with the Spring Usher, the May or July Highflyers although it may well overlap with the Autumnal Moth and perhaps even the Autumnal Rustic, and definitely the aforementioned November and December.

While its common name is rather unassuming and perhaps obvious given the season in which it the males are on the wing (the females are flightless), this belies a resilience and a resistance to the cold that many other creatures do not display. Indeed, while some warm-blooded mammals from hedgehogs to bears will seek out shelter and hide themselves away from the ice and snow during hibernation, this little creature is searching for a mate. Incidentally, the females simply crawl up tree trunks and exude sex pheromones to draw the attention of amorous males.

The females then lay a couple of hundred eggs in crevices in the bark of trees. The larvae don’t emerge until the spring when the daytime temperature reaches about 10 degrees Celsius. Historically, this would have been perfect timing for the larvae to feed on the newly opening leaf buds of their host trees. But, with climate change, that temperature is consistently reached several days before those tasty leaf buds have begun to appear. As such, many larvae that emerge when the temperature rises and the leaf buds have not yet opened simply starve. Evolution, however, has a way. There is evidence that some larvae that incidentally hatch later, when it’s warmer still, can feast on leaf buds. As such, they survive to mate as adults in the winter and so pass on their genes. Among those genes will, of course, be the ones that trigger them to emerge when the temperature is a little higher and so coincide with the opening leaf buds.

The moth’s scientific name is Operophtera brumata, the brumata meaning “short” and alluding to the length of the days at this time of year. I am not 100% certain of the etymology of the first part of the name, the genus Operophtera. Opero could mean I work and the second half could be “to destroy” from the Greek, or it could be a tweak on “wing”, which can be ptera or phtera, I believe. So, it could mean “I work to destroy” or “I work my wings”. Given that the larvae can ravage a small tree’s foliage leading to a halving of the tree’s growth that year, perhaps “I work to destroy” is apt.

I’ve recorded Winter moth since I began nothing, but not every year and only one specimen per season – 2018, then 2021, 2022, and now 2023.

For US readers, the closest relative is the Bruce Spanworm, Operophtera bruceata.

Nudist Snow Buntings

At this time of year, you might spot Snow Buntings pecking about the shingle and driftwood on a remote windswept beach, perhaps in north Norfolk or Dorset. One Studland birder tweeted earlier that this species has now reached their shores.

The birds are apparently on the beach edge just north of the nudist beach…

The twitter birder was at pains to point out to anyone who fancies seeing these birds that the nudist track is a “Wellies only track”.

It’s worth adding that there’s also at least one nudist beach where you might see Snow Bunts in north Norfolk. I have no idea whether Wellies are allowed there or not…but it’s less than 10 degrees Celsius up there and taking wind chill into account, I’m sure the local “club” won’t mind you carrying a muff, just in case it gets too nippy.

A November, or a Pale November, or an Autumnal Moth! Who knows?

This is a November Moth…or a Pale November Moth…or maybe an Autumnal Moth…it’s definitely one of the Epirrita species of moth, but I, and almost nobody else could tell you for sure which from this photo.

One of the British Epirrita species of moth — One of three possible moths, so we record it as Epirrita agg (aggregate)

But, it’s is one of those moths that could be any of several different species. You cannot know for sure unless you’ve raised it from larvae and know for sure what species you had, or you’ve done DNA testing but that assumes someone has the genomics for the various species, or you’ve done what lepidopterists call “gen det”.

Gen det, genital determination is where you dissect the male moth’s genitalia. Moth genitalia are markedly different even between otherwise very similar species and so you can identify which species you have from the bits you chopped up.

I am not going there.

So, my records simply say Epirrita agg, meaning an aggregate of all the possible species in the UK and no positive ID for any of them in particular.

There is, however, another British Epirrita species, the Small Autumnal Moth, which as the name would suggest, accurately for once in taxonomy, is actually smaller than the others and its wings markings are stronger. If you have one of those, you can assume you’d be able to distinguish it from the other three Epirrita species.

Moustached Reedlings – Bearded Tits

The Bearded Reedling, Panurus biarmicus, is the only known avian species in its genus. It was originally named the Bearded Tit because of its superficial resemblance to the Long-tailed Tit perhaps, but it is definitely not closely related to that bird nor any other tit.

Female Bearded Reedlings lack the "beard of the males — Female Bearded Reedlings lack the “beard of the males

The odd thing though is that the “bearded” part of its name refers to the facial markings of the males. They have long, droopy-looking black patches either side of their bills, whimsically resembling male facial hair but perhaps sideburns or moustaches rather than a beard. I’ve no idea why it wasn’t originally called the Moustached Tit. Either way, it’s not political correctness that is morphing the tit into the reedling it’s simply that it isn’t a tit, as mentioned.

Male Bearded Reedlings showing his "beard", which looks more like sideburns or a pair of moustaches — Male Bearded Reedlings showing his “beard”, which looks more like sideburns or a pair of moustaches

The species is sexually dimorphic, the “clean-shaven” females lack the sideburns/moustaches/beard as well as differing in size and other aspects of their plumage. They’re often quite shy and tend not to show well when it’s windy. That said, you can commonly catch small groups and sometimes larger flocks darting back and forth making their characteristic “pinging”, or “pew-pewing” contact call as the fly. When they settle on a reed, they often shuffle from a lower portion up to the top of the stem. On other occasions, they will dance about the lower parts of the reeds almost at water level.