Ousted cuckoo?

An adult male Lapland Bunting Calcarius lapponicus 

While surveying birds in northern Norway I came across a Lapland Bunting nest, which is not too unusual as they are common birds in the tundra there, although there was something different about this one. There were chicks in the nest as well as an unhatched egg and an eggshell, again nothing unusual there, except that the eggshell was of the wrong colouring for a Lapland Bunting egg.

The eggshell was a dull blue colour with brown freckling,
unlike the grey-brown background with scribbly line markings of the bunting egg

I immediately thought of a Cuckoo Cuculus canorus having laid an egg in the nest, so I checked the young to see if any were a cuckoo. None were, so what had happened? Thinking it through, the only explanation I can think of is that the buntings had detected the cuckoo when it hatched and ousted it from the nest.

The cuckoo egg did not resemble those of the buntings. It was more like a composite match between a Meadow Pipit Anthus pratensis and a Red-Spotted Bluethroat Luscinia svecica - two other common passerines in the area, and likely species to be targeted by cuckoos. Pipit eggs are grey-brown with dark brown freckles, and bluethroat eggs are dull blue coloured with tiny faint freckles. Yet this egg seemed to still pass unnoticed by the hosts.

The cuckoo eggshell on the left, the unhatched bunting egg on the right

I checked the nest a few days later and all the chicks, four, were alive and similar in plumage - all were buntings. So it seems that a cuckoo had failed in its attempt to dupe the buntings into rearing its chick. They perhaps detected the cuckoo chick when it hatched as different from their own and ejected it. This must happen more often than we assume, for there is an arms race between cuckoos and their hosts. In this case the cuckoo seemed to have laid its egg too late for the chick to gain the advantage of hatching first and ousting the buntings' eggs or newly hatched chicks.

Then, why had the cuckoo laid its egg in a bunting nest, were there too few pipits or bluethroat nests with eggs for it to parasitise in this late cold Spring?

The growing bunting chicks

Black-eared Cuckoo

A Black-eared Cuckoo has black ear coverts

Following a discussion on the Canberra Ornithologists' Group chatline on the identification of a young Horsfield's Bronze-Cuckoo Chrysococcyx basalis versus a Black-eared Cuckoo Chrysococcyx osculans, I would like to add a few pointers to the plumage differences as described in HANZAB (Handbook of Australian, New Zealand and Antarctic Birds). Unfortunately, I do not have an image of a young Horsfield's Bronze-cuckoo but I refer the reader to the photograph taken by Kym Bradley which opened the discussion on what species and age the bird was that she had photographed. To see the photograph click here to open the page in a new tab for comparison with the photographs taken by me of Black-eared Cuckoos below.

The following text is an abbreviated interpretation of the description on pages 705/6 of HANZAB vol. 4, and I have attached photographs to illustrate the features mentioned, adding further points of note where these are illustrated. The list of pointers described to differentiate between Black-eared Cuckoo (BEC) in all plumages and juvenile Horsfield's Bronze-Cuckoo (HBC) are as numbered in HANZAB.

A Black-eared Cuckoo in 1st year plumage
 - superficially similar to the young Horsfield's Bronze-Cuckoo photographed by Kym Bradley

(1) The BEC is much paler with more uniform upperparts and no conspicuous iridescence or pale scaling to the wing-coverts, as shown above.

Adult Black-eared Cuckoo - showing contrasting pale grey rump against the dark wings and tail. This bird has fresh plumage and as such, because the feathers are not faded by UV light, this bird is a s dark as any BEC is likely to be. 

(2) The BEC has a contrasting pale rump and upper-tail coverts (this is only in adult BEC) as above. The HBC does not have a contrasting rump, nor does a first year BEC. A first year BEC has only a slightly paler rump, see second last image below.

Adult Black-eared Cuckoo - showing buff-cream underparts
and dark chevrons on the under-tail coverts

(3) The BEC has a uniform buff to cream underbody with dark chevrons on the under-tail coverts in an adult, as above, or with no markings in a 1st year birds, as below. The HBC has a mostly white underbody and unmarked under-tail coverts.

First-year Black-eared Cuckoo - showing no barring on under-tail coverts

(4) The patterns on the head are more bold in the BEC; the supercilium is broad and square-ended and the black eye-stripe ends in a broad patch on the ear-coverts, as in an adult shown below. The HBC has a narrower and duller supercilium and eye-stripe.

Adult Black-eared Cuckoo - showing facial markings

A first year BEC has no eye-stripe, but does have a dark patch around the ear-coverts. It also has a pale buff-cream supercilium, lores and throat, as below. The pale colouring of the lores is contiguous with the supercilium, whereas a HBC has dark lores in all plumages.

First-year Black-eared Cuckoo - showing facial markings

(5) The adult BEC has a uniformly dark brown upper tail, with no obvious iridescence (there is s slight glow in the illustration) and a contrasting white tip, as below. The HBC has no white tip, is iridescent and has rufous edges to the base.

Adult Black-eared cuckoo - top side of tail showing white tips

A first-year BEC has pale tips to a dull uniform coloured tail, as below.

1st year Black-eared Cuckoo - showing pale (not white) tips to tail
Also note pale grey rump, but not of high contrast with wing and tail colouring

(6) The underside of an adult BEC's tail also shows a white tip, as below, and lacks the obvious rufous markings on the HBC.

Adult Black-eared Cuckoo - showing underside of tail with white tips,
and dark chevrons on the under-tail coverts

In summary, the bird photographed by Kym has: (1) an obvious iridescence on the wing coverts, which also show distinct scaling on their edges (so it is not a BEC), (3) the underparts are off-white/grey, not buff/cream (so not a BEC) and the under-tail coverts are unmarked (so not an adult BEC), (4) the supercilium and eye-stripe are dull and narrow with tapering ends rather than square-ended near the ear (so not a BEC), and the lores are dark (so not a first year BEC). As rump and tail tips are out of view in Kym's photograph points (2) and (6) cannot be assessed. One further feature of note is the dark grey band across the bird 's throat in Kyms' photograph, this is not mentioned in the HANZAB description (I can't find such anyway) and it does not show in any of the BECs I have photographed, so this could be an additional distinguishing point.

Therefore, in conclusion, the bird photographed by Kym was a juvenile Horsefield's Bronze-Cuckoo.

For further points on Black-eared Cuckoo plumage and age refer to my previous blog posts of November and December 2013.

Black-eared Cuckoo

It has been a rather hectic past few weeks, what with the Tawny Frogmouths fledging and doing a bit of general bird-watching around the south east of New South Wales and the ACT. I'll post as much as possible over the next few weeks, but meanwhile here are some shots of a Black-eared Cuckoo Chalcites osculans, which was caught during a regular study of birds at Charcoal Tank Nature Reserve, on the 9th November.

The trip was led by Mark Clayton as usual and in over eighteen years of study this was the first of this species caught there. The Black-eared Cuckoo is a national widespread bird, but rather uncommon and can be difficult to find by birdwatchers. So I felt it appropriate to add a few pointers on the bird's plumage to help others identify one if they do ever have the fortune to come across one.

The distinctive face of a Black-eared Cuckoo

There is no mistaking the bird as a cuckoo in Australia, but a couple of us with experience of northern hemisphere birds considered it as resembling a Northern Wheatear, due to its soft orangy plumage and dark eyestripe.

This bird had a rich pale orangy breast - a deeper colour than the expected buff

The under-tail barring is characteristic of the Bronze-cuckoo genus Chalcites.

The coverts on the wing were well worn and faded

The bird was quiet in the the field when we saw it and in the hand after it was caught, which might explain its elusiveness.

There was very little contrast between the underwing coverts and the faint wing bar across the primaries, secondaries and tertials

I did not see the underwing bar as being particularly noticeable in the field, nor in the hand. But the white tips to the tail caught my eye immediately.

The light grey rump contrasted with the back, wing and tail.
And the tail showed distinctive fault bars.

The overall glossy sheen on the back and wings was like those on other Bronze-cuckoos, although not so bright, nor green as in the other species.

Cuckoo chick

The birds' breeding season in Scotland is now well drawing to a close with many species feeding fledglings. This is tough enough when feeding their own young, but feeding that of a Cuckoo Cuculus canorus must be especially demanding for the adult birds which have been so duped.

A young cuckoo sits in a meadow pipit nest, well camouflaged under heather

Young Cuckoos can be very noisy when begging for food, but the go silent when approached. Then they rely on their cryptic plumage to hide them in the understorey of the heather moor where their foster parents, Meadow Pipits Anthus pratensis have their nest.

Young Cuckoo giving a defensive threat display

Once they know they have been detected, the young Cuckoos adopt a threatening posture, and flash their orange gape.

The young Cuckoo looks down from a fluffed-up posture

When relaxed they often take on a round, puffed out posture, holding their head back and extending a bulge of throat feathers, so typical of cuckoo species.

Young cuckoos have a bright orange gape

Their bright orange gape acts as an exaggerated stimulus for their foster parents to supply the extra amount of food required by the young Cuckoo above the demands of a normal brood of four smaller chicks.

The empty nest after the bird had fledged

Once the bird has left the nest, it is recognisable as having held a young Cuckoo by the widened and flattened shape of the nest cup.