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.

Young Honeyeaters

The gorgeous bib of a Striped Honeyeater,
the feathers from which it gained its species name lanceolata - spear-shaped

Continuing on from the previous post on aging birds caught and banded at Charcoal Tank Nature Reserve last weekend, here are some points on identifying young Striped and Fuscous Honeyeaters, Plectorhyncha lanceolata and Lichenostomus fuscus.

It is the head and shoulders that are striped,
and its bill is very finely pointed, from which it gained its genus name
Plectorhyncha - a spear point bill

Only one Striped Honeyeater was caught, which is understandable as they forage mostly high in the tree canopy. That was a first-year bird, moulting out from its immature plumage to that of an adult, ready to breed in a few months time. The bird had a fully striped head and shoulders like an adult, so the best feature to identify it as a young bird was the amount of buff tips to its wing coverts. The tips of its primary and secondary feathers were chipped and worn with notches and other pieces of the tips missing. This is a sign of age of the feathers, not of the bird, for it will moult these out and grow a fresh set once a year.

Worn and faded coverts, primary and secondary feathers of a young bird's wing

Buff tips on the greater coverts are often a good indicator of  a young bird's age as I have mentioned before. Here, the  two outer greater secondary, all the greater primary, and at least two median primary coverts have buff tips. The greater primary coverts are particularly worn at the edges. The fresh adult grey colour of the new inner secondary coverts and the alula contrast with and emphasise the faded and ragged old coverts.

The two outer greater secondary coverts are buff-tipped, all the greater primary coverts are faded brown and worn
 - while the fresh grey alula sits among them  

Only one young Fuscous Honeyeater was also caught, and although it was in immature plumage, with a pale base to its bill, adults also have this feature when not breeding. Other markings are more rigorously diagnostic of a young bird.

The plumage of a first-year Fuscous Honeyeater does not differ much from that of an adult

The species diagnostic feature of a yellow plume with a dark upper edge, on the side of the neck, was only beginning to grow in, and there was still a juvenile gape - the loose yellow skin at the base of the bird's bill.

There was only a hint of a yellow plume on the side of its neck

The back of the bird's head, from crown to nape, had flecks of buff feathers, very unlike the uniform grey-brown-olive colouring of an adult bird.

Buff-tipped feathers on the nape identify this bird as a bird in its first year

Olive-backed Orioles

First-year immature Olive-backed Oriole

I was banding birds at Charcoal Tank Nature Reserve again last weekend, with Mark Clayton, Harvey Perkins, Peter Ewin, and others. It is now late autumn and aging some of the birds is becoming difficult as they lose their juvenile and immature plumages ready to moult into full adult breeding plumage, before the next breeding season begins in a few months. Further species will be highlighted in later posts, but for now I have posted some images of two Olive-backed Orioles Oriolus sagittatus which we caught. One was a first-year immature bird and the other a second-year immature bird, which was particularly difficult to ascertain an accurate age for, as so many plumage features are comparative. Hopefully these images will help others to discern the ages of Olive-backed Orioles in future.

Second-year immature Olive-backed Oriole

The presence of buff-tipped wing coverts is always a good feature to look for in young birds and the first-year oriole had obvious buff tips on all its greater and median coverts.

Very obvious buff tips to the coverts - 1st yr

The second-year bird only had a few buff-tipped greater coverts, which were not obvious even when the bird was held in the hand. The second-year bird's primary, secondary and tail feathers were also darker than those of the first-year bird, similar to those of an adult.

Only a few buff-tipped greater coverts - 2nd yr

Adult Olive-backed Orioles have grey wing coverts with dark centres, and no buff tips. The image below is of an adult female's wing, from a photograph of a bird caught in a previous breeding season, when it was confidently aged as a breeding adult bird.

Adult wing coverts with no buff tips

The facial markings were also good for determining the birds' ages. The first-year bird had an obvious cream-buff supercilium, a dark eye and bill.

Obvious supercilium and dark bill - 1st yr

The second-year bird had a faint supercilium, red eye and a brownish bill with a pink flush. The streaking on its chin and throat are very similar to those of an adult female, and a second-year bird cannot be sexed until its plumage shows either a heavily streaked chin/throat or not, once its bill has become bright red.

Faint supercilium and brown bill with a pink flush - 2nd yr

The last two images are of adult Olive-backed Orioles caught in a previous breeding season at Moruya while banding with Anthony Overs. Neither bird has a noticeable supercilium, their irides are red and their bills are bright pink.

Adult female Olive-backed Oriole

Adult females have a streaked chin and throat, while the males have more of a green hood extending down around their throat. The females also have heavy streaking on their backs while the males only have light streaks.

Adult male Olive-backed Oriole

Lord Howe Island birds

Two Lord Howe Island Pied Currawongs on the summit of Mt Gower

Oceanic islands, far from large landmasses, often have a suite of unique fauna, and as Lord Howe Island is quite isolated, it has such a list. Unfortunately, as with many islands, some of the native species have been lost, a euphemism for having been eaten to extinction by man or animals introduced by man. Nevertheless, it still has the character of a wild island, especially up on Mount Gower (see previous post) and here are a few birds which added to my recent experience there.

The local subspecies of Pied Currawong has a longer, narrower bill than the nominate race.

As we climbed up through the forest to the plateau, loud chuckles and coughs followed us from the thick canopy. These were the calls of the local Pied Currawongs Strepera graculina crissalis, which have a distinct island accent, and they seemed to be telling one another of our approach.

A little more secretive, but never timid, and quite happy to forage around our feet as we passed, were the Woodhens Gallirallus sylvestris, This flightless species was saved from extinction, by the collection of a group of birds which had escaped predation on the almost inaccessible summit plateau, screened off from pigs etc by cliffs. The birds bred successfully in captivity and now that birds are running wild in the lower forest as well as the plateau, the future looks bright for the species.

 Lord Howe Island Woodhens forage for food in the rich basalt and leaf-litter soils 

Meanwhile all around, there is the incessant calling of Providence Petrels Pterodroma solandri in the sky.

Providence Petrels wheel around the Mt Gower cliffs

Ocean, cliffs, high hilltop, mist forest and flocks of petrels - a wonderful experience

There aren't many viewpoints out from the plateau as the forest is so dense, but looking out over the ocean from so high added an extra quality to the scene. Then our guide, Dean, called some petrels down. All he did was give a few yodels and in they came, crashing through the canopy and onto the ground.

Some petrels landed clumsily on branches

Others crashed to the ground and immediately started to squabble

They had no fear of us whatsoever

Unfortunately for the species, due to their disregard for humans, Providence petrels were eaten to extinction on neighbouring Norfolk Island. They were so easy to kill. There were more people on that island than Lord Howe, as there still is today, and it is probably lucky for the birds that Lord Howe has never been highly populated by man. Although who knows what hidden anthropogenic dangers might still wipe them out - they eat plastic debris in mistake for food, it accumulates and fills their stomachs, eventually causing death by starvation. Let's hope this doesn't lead to another extinction.

To see a clip of David Attenborough calling down Providence Petrels on Lord Howe Island click here