Seabird flight

Two Kittiwakes soaring over the sea

While visiting some seabird colonies on the Scottish coast recently I took a few images of the birds in flight to capture their comparative morphology and technique. For each has its own, which fits the species' life.

Herring Gulls have a heavy appearance 

Herring Gulls, like most gulls are more land birds than seabirds, for they forage onshore, often well inland, as much as at sea. Even when at sea they mostly inhabit coastal waters. So these birds have a generalist type of flight; they can soar and they can flap with deep strokes. They are recognisable by their strong, bulky body and thick set appearance.

Kittiwakes have a straight edged tail and bent wings even when gliding

Kittiwakes are true oceanic gulls. They are light buoyant fliers, only coming ashore to rest or nest. Most of their lives are spent foraging out at sea, where they glide, flutter and dip into the surface waters for food. These are delicate gulls, recognisable by their slender build. It is not so much their colouring or markings that identify them, but their agility and knack of switching from a long oceanic gliding flight to a tern-like fluttering dance, with their legs hanging down as they dip for food.

Fulmars have rounded tails and their wings are held rigid most of the time when flying

Fulmars are true seabirds. They spend most of their life on the wing, gliding on stiffly-held wings as they flip low over the waves. And they seem to fly more easily the stronger the wind. They might be clumsy on land when they come ashore to nest, waddling on their short weak legs as they scrabble onto their nest ledges. But those short legs are suffice for their purpose, when out at sea, they are an advantage, as they are tucked into the body feathers and never hinder the birds' aerodynamics. The whole bird is a slick flying form, using the wind for lift and thrust, and they are a delight to watch as they wheel around and around the airspace off the nesting cliffs.

Fulmars, like all petrels and albatrosses are true masters of oceanic flight

I have not mentioned the auks or shags which also breed on the Scottish coast, for they are more swimmers that fly, than flier that swim like the birds listed above. The auks' and shags' forte is their diving ability - they swim underwater.

Precocial and Altricial young

Birds in Scotland are busy hatching and rearing their young at the moment, with June being the month when most species have dependent young at some age. I have been ringing, with other members of the Grampian Ringing Group, various species of chicks from common and tiny Willow Warblers to large and rare Golden Eagles, and all sorts between. While doing so, I have as ever been impressed by how well each species has adapted the best method of post-egg development to suit its lifestyle.
 

Common Gull eggs, with cracklines and holes - the chicks are beginning to hatch

I have been ringing gull and wader chicks and took a sequence of photographs at one Common Gull colony to show the development of their chicks. The typical clutch size is three eggs and the chicks hatch one after another, over about two days. The first chick to hatch stays in the next and are brooded by the adult birds until the last chick hatches and dries. Then they all begin to wander from the nest, usually set on the ground, and hide beneath the surrounding vegetation.

One dry chick, one wet chick and one still on its way out

Gull chicks have cryptically-coloured down which keeps them concealed from predators and warm. They can walk sand run strongly and are known as precocial young.

A fully dry Common Gull chick - two days old and now three metres from the nest

Or rather, gull chicks are better described as Semi-Precocial young, those which are downy and can walk and can leave the nest soon after hatching. e.g. in the case of terns and gulls, although they still rely on their parents for heat and nourishment.

True fully precocial, self-dependent young would be such as Mallee Fowl which find their own food without even guidance from either parent.

This is so different from the familiar nestling birds, which are Altricial - where the young are naked, blind, weak-limbed at hatch and rely totally on their parents for food and heat.

Semi-altricial young such as raptors are downy at hatch, but weak and rely on their parents for heat and food.

Four Skylark chicks in their nest

Two other terms which are used to describe young birds are; Nidifugous - those that leave the nest soon after hatching, generally once the whole brood has hatched and their down dried, and Nidicolous - those which remain in the nest for several days or weeks after hatching.

A three-day old Skylark chick, still partially naked and blind

The nestling stage is a very vulnerable period for young birds and the variety of concealment and protection methods taken by the parent birds is, to me even more fascinating. From secretive single nests to noisy colonies, each works for the protection of different species. But more on that later.

Five kestrel chicks - ranging from about one to two weeks old

Ringing Golden Eagle chicks

Golden Eagle habitat in ancient pinewood of the eastern Highlands

As it is now the second week of June, the Golden Eagles chicks in Scotland are well grown, between three and five weeks old. So it is time to ring them while they can be handled easily and safely, for the birds' sake, more than ours.

I was out helping Ewan Weston ring the chicks in some of the nests which he monitors and in three that we checked, all had twins. This is a sign of plenty food and fair weather, and now that they have reached this age, they should all fledge. His study area is in the eastern Highlands and all three nests were in Scots Pines, magnificent old trees

An eyrie set on the upper branches of one of the pines

The adult birds gave a silent fly-past as we approached the nest tree, then they slinked off to watch us from a distant perch. Meanwhile the chicks remained silent too, lying flat and inconspicuous in the eyrie until Ewan came within reach and showed his head over the edge of the nest. He then gently placed them into a bag and lowered them down to be ringed and measured on the ground.

One eaglet sits up on the nest while the other lies low on the far side

In each of the three nests, there was one male and one female chick - the females recognisable by their larger size, especially that of their feet, legs and head. The flight feathers on Golden Eaglets begin to show dark against the white down when the chicks are about four weeks old, and the birds generally lie quietly when laid in the heather below the eyrie while they are ringed. When older, some will strike out with their talons, and hiss, but they seldom snap with their bills.

The chicks were lowered down the tree in a bag for safe processing on the ground

Simon Cherriman from Perth, Australia, who is visiting Scotland with me at the moment came along to learn how we ringed eagles and Jenny Lennon, Ewan's partner, helped guide him through the process. Although the chicks were docile, the rings need to be extra-strong, so that the birds cannot open them and take them off once fully grown. And so, the rings are especially tough to fit and close securely.

Ringing one of the chicks

Each bird was fitted with a standard ring issued by the British Trust for Ornithology, and a colour-ring on the other leg which can be more easily read if the birds venture into the line of view of many of the remote cameras which are being set up throughout the Highlands. This will help to inform us on how much interaction there might be between Golden Eagle home-ranges. Anyone visiting eagle eyries or ringing of eagle chicks must have a licence from Scottish Natural heritage to do so and we were all covered for the work we were doing.

Each bird was fitted with an individually numbered colour ring 

It only took a few minutes to ring the chicks then they were measured to ensure that even if it looked like the larger birds were female they did in fact fit the criteria.  

Several measurements were taken to determine which sex the chicks were, here the hind claw

These young birds already had large talons and bills, but wait until they are fully grown. Then they are really impressive.

And their heads were measured

Ewan, Jenny and I have ringed lots of eaglets the years, so all was done most efficiently and the birds were passed back up the tree. Then we were gone. The chicks lay quietly in their nest and the adults would soon return - as quietly as they left.

And the birds were all set to be returned to the eyrie

Predation of Greenshank eggs by crows

An adult greenshank fitted with a geolocator on a leg ring

While studying Greenshank in northern Scotland recently, it was again apparent that some of these birds are being predated by Hooded Crows eating their eggs. This was also noticed in the past two years of the study, a joint project between Ron Summers, Brian Etheridge, Nick Christian and myself, which is focused on marking the birds with individual colour-ring combinations and geolocator tags to discover where the birds which breed in Sutherland migrate to in winter and on passage.

A greenshank egg, sucked by a  Hooded Crow and the remains of another on the edge of the nest

Two clutches of eggs, from eight found, were definitely lost to crows, as evident from the distinct holes in the side of the eggshells left at the scenes. Two other clutches might have been taken away by crows, they can lift and carry them away from the nest to eat elsewhere, often next to a pool of water, but as there was no evidence at the nest sites, they could possibly have been taken by egg-collectors. Not that that is any better news for the study.
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The large hole in the side of the egg, with angled notches left by the crow's bill are indicative of the predator type

Once the birds have lost their eggs they are likely to leave the area to perhaps nest somewhere else, or abandon their breeding attempt for the year. The crows do not nest on the moors where the greenshank nest, they come up from nearby croftland where they find food all year round. Food is scarce for them on the moors in spring, but they probably know there are eggs to be found there and they have been seen walking over the ground searching for any food they can find, including eggs.

A typical clutch of four eggs in a Greenshank nest 

There is not much known on the effect of this predation on the greenshank population, and it is only during intensive study that such information is gained. Perhaps, as the greenshank live for several years or more, they only need to raise chicks successfully once to maintain the population. But then, we do not know what other impacts there are on the birds in their wintering area, and that is why we consider it needful to know where they go.

Greenshank chicks hatching, two have already left the nest. The hatched eggshell is typically holed around the broad end and there are red blood-marks on the inside membrane

Greenshank are not the only birds of the moor which the crows take eggs from. Meadow pipits and skylark are the most abundant species there, and they even find secretive nests like that of Teal, one nest of which I found deserted after crows had taken one egg from the nest and sucked it. They had also rolled another egg out of the nest, but as there were still five eggs in the duck's nest, it seems that she manged to scare off the crows. However, she abandoned the nest after that, probably from fear of future attack.

A Teal's egg, sucked by a crow, with yolk spilled on the edge of the hole

Teal nests a can be placed almost anywhere on a moor, hidden under heather, and I would not have found this nest if the eggs had not been uncovered and obviously abandoned.

The abandoned Teal's nest and eggs, cold and uncovered.
A duck always covers her eggs when leaving the nest to feed

  Inland Thornbills
- Differences between plumages of old and young birds

Adult Inland Thornbill
- showing a smoky grey upper plumage, very fine white scalloping in its forehead, and a pure black bill

When catching birds on a recent trip to Charcoal Tank Nature Reserve as described in the previous two posts we caught several Inland Thornbills Acanthiza apicalis albiventris. The bird illustrated above was caught on an earlier trip during the breeding season and was confidently aged as an adult bird. Those illustrated below are young birds, hatched in the previous spring, i.e. about October/November 2013.

Face of 1st year immature Inland Thornbill (older?)

Face of 1st year Inland Thornbill (younger?)

The bird on the left is developing a dark grey crown, similar to the adult bird, but the scalloping on the forehead is still buff-coloured. The narrow buff tips creating contrast between the scalloping and background colour, although not as strong as on the adult bird.













The second young bird, left, has a pale green/grey crown and forehead, with broad buff tips to scalloping, creating less contrast between the scalloping and background colour.

Profile of 1st year Inland Thornbill (older?)

In profile, the developing grey on the crown of the first young bird shows the dark head with fine buff scalloping, concentrated on the lower forehead. It also has a dark bill, but not fully dark as in an adult, especially at the base of lower mandible

Profile of 1st year Inland Thornbill (younger?)

In profile, the second young bird has a paler head, with less contrast between the background colour and the buff-coloured forehead scalloping, which extends well above the eye. The base of bill is yellow/buff, and the rest of the bill is dark grey, not black as on an adult

Wing of 1st year Inland Thornbill (older?)

Although these birds were not of exact known-age, as they had not been trapped and marked before, it would seem that young Inland Thornbill plumage progresses from broad buff-coloured scalloping on the forehead, through fine buff-tips, to fine white-tips by the time they reach adulthood. And the crown changes gradually from greenish-grey to smoky grey over the first year.




The first-year birds also retained some of their first-grown flight feathers. The first (older?) bird had three old outer primaries, and the inner primaries were recently moulted and freshly grown.

Wing of 1st year Inland Thornbill (younger?)

The second of the young birds still had all of its first-grown primary feathers, from its juvenile plumage.

The combination of all these features support that the second young bird was younger than the first, but only the recapture of known-age birds will help to confirm these ideas.