Category: Biology

Avian ancestry

Our feathered friends, the birds, are all descended from the dinosaurs. Specifically, birds evolved from the hollow-boned theropod dinosaurs which includes the Tyrannosaurus rex. All 10500 species of bird alive today and all the many thousands of others that are extinct came from the dinosaurs. But. Didn’t the dinosaurs die out 65 million years ago when a huge asteroid hit the Earth, you ask? Well, most groups that were still around at the time did, allowing the mammals to fill the ecological niches left empty by their sudden absence. However, the lineage of those hollow-boned dinos would persist too. The question is how did they survive when their cousins died out?

Writing in the journal scientists affectionately know as PNAS, researchers explain how they have found another adaptation that could have given the ancestor of the birds an advantage when things got very tough for the other dinosaurs. They have examined the fossilized lungs of a bird ancestor, Archaeorhynchus spathula, using scanning electron microscopy and found features in the lungs of those animals that resemble those of modern birds and are thought to be an evolutionary adaptation that supported flight include unidirectional airflow in the lungs, supplementary air sacs, and lung tissue that is finely subdivided to maximize surface area and so absorption of oxygen from the atmosphere to drive the huge energy requirements of flying.

Crocodilians are the only other living creatures that have unidirectional airflow and this characteristic is now thought to have evolved even before the ancestors of the early feathered dinosaurs.

The authors also discovered among the preserved plumage of the fossil a pintail feather structure that has not been seen in other known birds of the Cretaceous period but is seen in some modern birds. The researchers suggest that all of this evidence stacks up to the fact that key avian structures were in place by the Early Cretaceous and could have been what helped the ancestors of modern birds survive the extinction of the other dinosaurs.

“Archaeorhynchus preserving significant soft tissue including probable fossilized lungs,” Xiaoli Wang et al. Proc Natl Acad Sci (2018)

Female Cross Spider – Araneus diadematus

Cross, or European Garden, Spider (Araneus diadematus), also known as the Crowned Orb Weaver, Diadem, Orangie, and also the Pumpkin Spider, so perhaps I should’ve held off posting this until Halloween. There is, however, another spider that has the vernacular name Pumpkin Spider.

This is a female specimen. The legs of orb-weaver spiders are specialized for spinning orb webs (although this one had spun a flat web across a small windowpane). The spider constructs its web and then hangs head down in the centre or in nearby foliage, with one claw hooked to a signal line connected to the web waiting for a disturbance as prey enters the web. The spider bites its prey and quickly envelops it in silk. Some enzymes paralyse the prey and preclude the prey biting or stinging the spider. Other enzymes begin the liquefaction (digestion) of the prey’s innards ready for consumption.

Just for the record, this is one of those spiders that cannibalises the male after mating.

I asked arachnid expert Dr Richard Pearce (@DrRichJP) about the fact that spiders seem to have extra pairs of eyes and wondering why other creatures did not follow this evolutionary route. This is what he had to say:

Spider eyes are not necessarily comparable to our own. Many spiders have poor vision. Those with good vision tend to have two primary eyes to give binocular vision (e.g. jumpers - Salticidae; wolf spiders - Lycosidae). The other eyes do not form images in the same way.

Spider photo now in my Invertebrates gallery (non-lepidoptera)

RSPB Ouse Fen

I’m always hopeful of interesting sightings along The Reedbed Trail at RSPB Ouse Fen. Saw lots of Hobbies and Terns as well as Marsh Harriers and Warblers there earlier in the year.Visited today with Mrs Sciencebase, two or three Marsh Harriers in evidence, lots of gulls, a single Kestrel, one or two Buzzard, big Lapwing flock, Grey Heron, waterfowl, Little Egret, Goldfinch, Reed Bunting, Green Woodpecker, Stone Chat pair, and the pew, pew, pew sound of Bearded Reedlings of which we saw a few but didn’t get any great shots. But, at least confirmed what I thought I heard earlier in the year and nice to know they’re colonising a local reserve. Oh, and as we were leaving, we saw a fox, other visitors with dogs unwittingly scared it into the trees.

Buzzard (Buteo buteo) takes flight

Female Reed Bunting (Emberiza schoeniclus)
Mrs & Mrs Stonechat (Saxicola rubicola), RSPB Ouse Fen, VC29

Bearded Reedling wouldn’t turn to the camera before flying off!

Goldfinch alighting on barbed wire fence at RSPB Ouse Fen
Some of a flock of 500 or so Lapwing over RSPB Ouse Fen
Vulpes vulpes at RSPB Ouse Fen

Green-brindled Crescent

Isn’t it time to put the scientific moth trap away, they asked. Surely there are no moths flying in the autumn and winter. Well, there are definitely fewer species around now, especially if it has been really damp and chilly overnight. But, there were numerous last night feeding on the ivy blossom: Centre-barred Sallow, Large Yellow Underwing, Vine’s Rustic, Common Plume, and one or two micro moths.

In or around the trap, more Yellow Underwings (Lesser, Small, and Large), Setaceous Hebrew Character, White Point, Lunar Underwings, and a Red-green Carpet.

 

This morning some of those were still in attendance, but a Green-brindled Crescent (Allophyes oxyacanthae) had taken over the morning shift from the RG Carpet. This species was first curated by Linnaeus in 1758, it grows to between 35 and 45 mm according to the UKMoths page. It’s prominently green in colour, but subtly striped (the brindled part of its name). The crescent in its name refers to two white curves on its wings. It has unusually large oval and kidney marks compared with many other noctuid (owlet) moths.

It is mottled brown mainly but catch it in the right light or under the glare of a camera ring flash and its gree metallic scales will shine through. It commonly flies from September to November and is found across the UK, in woodland, hedgerows, and the suburbs, its caterpillars feeding on hawthorn (Crataegus) and blackthorn (Prunus spinosa) and other trees and bushes.

Barn Owl pellet

TL:DR – Barn Owls regurgitate pellets containing the indigestible bones and fur from their prey. It is possible to dissect these owl pellets and to find out what the owl has eaten from the debris.

Barn Owl (Tyto alba) hunting over Rampton, VC29If you have ever stopped to think about the gustatory habits of owls, then you have perhaps wondered what happens to all the bones and fur from the little creatures on which they predate after they eat them.

Dry Barn Owl pellet, obtained from WWT Welney

Well, avian digestive enzymes do not have the capacity to break down bones and fur and as the flesh and organs are digested those materials accumulate in the upper gastrointestinal tract forming a hairy bolus, a pellet, that ultimately the owl will regurgitate. A pellet forms after six to ten hours following a meal in the bird’s gizzard, its muscular stomach. Owls and other birds of prey bring up the indigestible material from the proventriculus, their glandular stomach. The pellet is thought not only to get rid of indigestible waste materials that would not pass downwards safely but also to scour parts of the digestive tract, including the gullet to remove detritus that might harbour pathogens.

Single fragmented owl pellet soaking in water

Now, the experimental bit.

I collected an owl pellet (with the warden’s permission at WWT Welney on a recent visit and followed his instructions to soak the pellet in water for a number of hours and then to tease it apart to reveal the bones within its proventriculus, or glandular stomach.

First teasing apart of owl pellet

After about an hour’s work I’d dissected the pellet to reveal a relatively large skull and separated lower jawbones of presumably a vole as well as various femurs, tibia, fibula, scapula, a few vertebrae and lots of rib bones, and perhaps another couple of much smaller skulls the extraction from the of the pellet I did not have the patience nor the equipment to pursue with the necessary care and attention to detail. I did not find any feathers nor insect exoskeletal parts or wings in this pellet. All the remains were rodent mammal.

Rodent (vole?) mandible next to skull extracted from owl pellet

Anyway, I am quite pleased with the produce harvested from my first owl pellet dissection. Mrs Sciencebase points out that she did the very same experiment as a biology student many moons ago.

Boney bits and pieces
Rodent bones after a bit of a cleanup
Rodent skull next to centimetre scale
Rodent jawbones
Rodent lower hindlegs – tibia and fibula

Other birds, including the fish-eating, insect, and carrion-eating birds, grebes, herons, cormorants, gulls, terns, kingfishers, crows, jays, dippers, shrikes, swallows, and most shorebirds also produce pellets.

Cranes at WWT Welney

UPDATE: Just over 5 years later, night of 7th November 2024, 83 Cranes into roost at Welney.

There is a flock of 37 Cranes (Grus grus) at WWT Welney in Norfolk at the moment. Some of these have bred on the reserve, all of them, it seems, share their time between this site, NT Wicken Fen, Kingfisher’s Bridge Nature Reserve, RSPB Lakenheath, and the Ouse Washes.

Photos were taken from the Visitor Centre viewing platform, fully zoomed (600mm on a full-frame SLR) and cropped. The birds were about 900m away so the photos are not particularly distinct.

 

European Robin – Erithacus rubecula

It occurs to me occasionally and I forget to mention it, that this is probably the species of bird we Brits probably picture when we hear the song Rockin’ Robin.

I suspect, however, that the guy who wrote the song, Leon René (aka Jimmie Thomas), was actually thinking of the American Robin (Turdus migratorius), which is like a British Blackbird (T. merulea) or a Song Thrush (T. philomela) but with a red/orange breast.

Anyway, the American Robin’s song is much closer to the refrain “Tweet, tweedle-lee-dee” in the hit, than the rambling and melodic song of the European Robin. One more thing, check out the cover artwork of the record by original Rockin’ Robin artist, Bobby Day, he’s got macaws, parrots, but no sign of a Robin, American, European or otherwise as far as I can see.

Now, here’s a thing…mammals have a single set of vocal folds in the larynx of their trachea. That means they can only really ever bark, moo, yelp, or sing with one voice using that set of vocal folds. The “voicebox” of birds is further down their pipes at the place where the trachea branches into two bronchi. Birds have a syrinx* rather than a larynx, which allows them to create two tones at once.

The European Robin (Erithacus rubecula) is an old world flycatcher. Like I say, not to be confused with the American Robin demonstrating what is possible with a syrinx. Listen out for his neighbours calling at the points in the video when he stops singing. It’s impossible to know who sang first, maybe he’s replying, or maybe it’s them calling back to him.

For Rush fans, yes, that is the reference! The Temples of Syrinx from the 2112 opus. In classical Greek mythology, Syrinx was a nymph and a follower of Artemis, the goddess of the hunt.

Syrinx was known for her chastity, making her the perfect object of worship for the Priests of the Temples of Syrinx who by the year 2112 have banned pleasure (specifically music played on guitars) from the world in deference to computers. In Greek mythology Syrinx was pursued by Pan, the god of the wild and music.

To evade his advances, she fled into the river Ladon, where she asked the gods to turn her into reeds. Pan, of course, took those reeds and from them fashioned his panpipes, ultimately possessing Syrinx for his own pleasure. This myth is why the word syrinx is used for the double vocal flute of birds.

Conkering spiders

I’m not entirely sure why anyone would want to exclude spiders from their home, my preference would be to have a flyeater in each corner of the room to eat the flies. Flies spread disease. Spiders modulate diptera activity.

Anyway, every autumn, the deceived wisdom that putting conkers, the seed of the horse chestnut tree,  Aesculus hippocastanum, around your home will scare the spiders away comes up. It’s evergreen content for columnists. But, it is a myth, it has been debunked several times over the years.

More about conkers coming soon in my Materials Today column.