Saturday 9 September 2017

Mist-netting birds

Owlet Nightjar Aegotheles cristatus
I was out mist-netting birds last weekend at The Charcoal Tank Nature Reserve, New South Wales, on a trip organised by Mark Clayton. The aim is to catch a sample of birds several times a year as part of a long-term study of the changes in the numbers and species in the bird population. The nets were set the evening before and opened at first light, hence we caught this nocturnal bird, an Owlet Nightjar. This is the first I have seen caught in almost-daylight. Perhaps it had been feeding late because it was a cold night at the end of winter and there were few insects about.

Small, quiet, with big dark brown eyes, a long tail, and dark grey plumage
- all ideal for a nocturnal woodland bird

Owlet Nightjars are neither owls nor nightjars, they are classed in a family of their own, Aegothelidae. They roost by day in tree hollows and hunt at night, feeding on invertebrates, mostly insects, which they can catch in flight although they spend much time foraging on the ground. They are small dainty birds, only about 50g in weight, and they have a soft plumage similar to owls and frogmouths, for quiet flight.

Horsfield's Bronze-Cuckoo Chalcites basalis
- the broad dark stripe over its ear coverts and the scalloped,
 buff tips to the wing coverts are diagnostic markings of the species
As the day opened up we heard four species of cuckoo calling: Pallid Cacomantis pallidus, Fan-tailed C. flabelliformis, Shining Bronze-Cuckoo Chalcites lucidus and this one, Horsfield's Bronze-cuckoo. We caught four of this last species and all were males, indicative of how male cuckoos, and many other species of birds, tend to migrate to their breeding grounds ahead of the females. The tail patterns, both topside and underneath, are diagnostic of the species' sex - the females have russet colouring on the outer tail feathers, the males, like this one, have black and white outer feathers.

     Top-side of Horsfield's Bronze-Cuckoo's tail     
    Underside of tail

We caught a good number of regular breeding birds of the area especially White-plumed Honeyeater Ptilotula penicillata and White-eared Honeyeaters Nesoptilotis leucotis for comparisons of biometrics. Our sample included a good mix of species; some resident, some returning to breed and some migrants passing through. There were examples of two races of Silvereye, Zosterops lateralis; the local Z.l. westernensis and the migrant Z.l. ochrochorous which breeds on King Island in the Bass Strait. We also caught fifteen Striated Pardalotes Pardalotus striatus at once in one net and there were three races in that flock; P.s. striatus which breeds in Tasmania, P.s. substriatus which breeds in the interior of the continent and P.s. ornatus which breeds in the south-east.

Z.l. westernensis 


Z.l.w. Rufous flanks

Z.l.o. Tawny flanks

Z.l.w. Yellow throat

Z.l.o. White throat with yellow flecks

Perhaps, the most spectacular bird we caught was a male Brown Goshawk Accipiter fasciatus in full breeding plumage. Accipiters are aggressive and can inflict cuts with their bills and talons, so great care is necessary when handling them. This powerful predatory bird was such a contrast from the docile Owlet Nightjar we began the day with.

The talons are grasped firmly and the head held up away from our hands.
The whole bird is kept well away from our faces.

The bird had clean, slate-blue upper coverts and head. Its breast and underwing coverts were solidly barred.
All its flight feathers were complete, no moult.

The rounded tail is one of the better features to look out for if in doubt whether a bird seen is a
Brown Goshawk or a Collared Sparrowhawk Accipiter cirrocephalus, which has a square-ended tail.

The bright yellow eyes of an Accipiter - a determined hunter.
Note the heavy eyebrows, these shield the eyes, not only from sunshine, but against twigs and leaves when a goshawk crashes through thick vegetation in pursuit of its prey. The brows are unfeathered and the skin shows signs of abrasion. One of the honeyeaters we caught had a 4mm long thorn stuck in the skin on its crown, an example of what birds have to contend with when flying through woodland. I pulled the thorn out cleanly and the honeyeater flew off happily.

All the birds we caught flew off back into the bush. No animals were harmed in the making of this blog. 

No comments:

Post a Comment