Sunday, December 31, 2006

In Search of the Horsfield's Bronze-Cuckoo

Ever since John Tongue mentioned, sometime ago, that he rarely saw Horsfield's Bronze Cuckoos, I've kept an eye out for them. During the Spring and Summer, I've come across, and several times photographed, Shining Bronze-Cuckoos, but rarely heard or seen the similar looking Horsfield's. In fact, I have seen Horsfield's in only 2 locations. Early in the Spring, there was a pair near the gate in the Meehan Range, and more recently, I've seen them in the Risdon Brook Park. So this morning, with rather overcast conditions, but very still, I spent an hour or so, trying to find the Horsfield's.
I had seen Horsfield's in the same location at the Risdon Brook Park on a couple of occasions recently, so decided to concentrate my search there. It's an area on the eastern side of the park that was obviously once farmland. It consists of fairly open poor, rock strewn, pasture, with native grasses and old acacia trees, and a few young eucalypts now growing through. Perhaps, significantly, it's one of the areas where I have seen numerous flocks of Yellow-rumped and Brown, Thornbills. Both of these species build domed nests, which together with the Superb Fairy-wren, probably are the main species parasitised by this cuckoo in Tasmania. Apparently, some Fairy-wrens have developed an ability to recognise young Horsfield's and frequently abandon them (you can find more on that subject on the internet). I wandered around this area for some time, noting Pallid and Shining Bronze Cuckoos calling, before a short call that I couldn't identify, caught my attention. It had the 'quality' of a cuckoo, sounding somewhat like part of the Pallid's repertoire, but a different tone, certainly not a call I had previously associated with Horsfield's. Walking towards the source, I was passed by a small light brown bird travelling in shallow undulations, but fast--the first Horsfield's, a juvenile. The next hour was filled w
ith some exasperation. I eventually found what I assume was the same bird, but this time it was with an adult (image at left). I was quite surprised to find an adult with a juvenile, given that the adult hadn't reared the youngster, but perhaps this regularly happens once the juvenile is fully grown and leaves the host parents. I tried hard to get meaningful photos, but the poor light conditions, and the timidity of the birds, made this difficult and the shots shown here were taken from 50 or more metres away. My overall impression of the Horsfield's Bronze-Cuckoo in the South East at least, is that it has significantly declined since the 70's. I note that my sightings have both been at sites where Yellow-rumped Thornbills are common, another species that has also declined in that time frame, largely I suspect from habitat loss and possibly changing farming practices. Whether there is any real connection is supposition on my part, but it might explain the cuckoo's decline.


Happy New Year to You All

11 comments:

John Tongue said...

Hi Alan,
Happy New Year!

Nice shots, expecially given the conditions you describe. And interesting info about this elusive species, too.

Maggie Cashman-Bailes, of Birds Tas reports seeing numbers of Horsfield's, LAST year, now, as does Ron Spencer, but we still find them seldom. In fact, in four years living in Tassie, we have only SEEN them at Arthur River, and King Island, though we have heard them a couple of times in other spots.

We may have to check out Risdom Brook Park for the Twitchathon!

Happy New Year to all readers. My new years birds so far (8:30, but not been up for long) are Turtledoves and Blackbirds!

BirdingTas said...

Hi John,
Happy New Year to you too.

I have to say that I've been to many spots around SE tas. during this "season", and I have heard and seen many 'Shining', but only heard or seen 'Horsfield's' as per the the blog. I'm beginning to form the opinion that some of the 'Shining" are being mis-IDed. The use of the 'diagnostic' discontinuous barring, (for Horsfield's), should not be used, as I hve seen this in quite a few 'Shining' too. Bronze-Cuckoos often take up a'dishevelled' pose, not sure why, but it does make the barring difficult to adequately see. Barring that continues up to and under the chin is diagnostic. Markings around the face are not always easy to adequately see either. I've mist-netted quite a few of both species , and they're not easy to seperate in the hand either!

BirdingTas said...

Forgot to mention that I drove around Pipeclay Lagoon and return, and by 9.00, I had clocked up 31 species--without getting out of the car!

John Tongue said...

31 by 9:00am is not bad - we're probably glad you haven't registered for the Twitchathon!!!

BirdingTas said...

Should have added that I also took 142 digital photos, some for a future blog, so I didn't have much time to birdwatch! I have been lucky enough to have been on the winning teams in long past twitchathons.

Duncan said...

I've seen adult and juvenile Horsfield's together over here in Gippsland, Alan, towards the end of summer when they're probably getting ready to make a move.

BirdingTas said...

Hi Duncan,
Thanks for the comment. I can't recall ever seeing them here together, but as I see so few anyway, my chances are slim! Having been brought up by foster parents, presumably they innately know what their real parents look like. Have you had a decline in numbers over the years.

Duncan said...

I don't see many Alan, but numbers seem stable.

John Tongue said...

Hi all,
We've only been ( or been back) in Tassie for four years, and numbers of Horsfield's have always seemd low, so maybe the decline has been on for some time. Always lots of Shinings, Pallids and Fantaileds, so I wonder what's upsetting the Horsfield's. Maybe it is a decline in host species?

BirdingTas said...

Hi John,
While mistnetting, back in the 80's, I cauight a number of bronze-cuckoos, and they were about equal in number. It was not unusual to catch both species in the same habitat, mostly acacia scrub. So they were, in my opinion, reasonably common. As I mentioned in the blog, the Yellow-rumped Thornbills, a common host species, have declined. I can take you to many areas where I have found them breeding in the 70's, and even 80's, where you would be pushed to find any today. Whether that's a cause or coincidence is unclear.

John Tongue said...

Sounds plausible, Alan. If the hosts decline, then presumably, over time, there are fewer young cuckoos born, and so fewer adults to return to their birth-district (I'm guessing young cuckoos return to much the same area where they came from for breeding??).