01 July 2006

Chifley Chronicle #8

Last week in June 2006
Excitement continues over the Grey-headed Lapwing Vanellus cinereus seen recently at Burren Junction between Narrabri and Walgett in central northern NSW. Truckloads of the keenest twitchers have made the journey up to see it this week and as far as I can tell all have been successful though it is sometimes a very frustration bird to locate; seeming to disappear for hours on end and by all accounts it is rather 'flighty'. Few pictures of the bird have emerged on the net so far but I am sure they will soon be flooding in!

For me it has been the week for a return to Tidbinbilla to collect the sound samples from our automatic recording station (see posting last week). I did this job on Thursday and it was a calm sunny day following a hard overnight frost with temperatures again down to -8C in many places. Before collecting the tape recorder and the other gear from our study site I decided to have another try at sound recording the Australasian Shoveler that have been regularly present on the ponds in the waterfowl area at Tidbinbilla.

I found that the additional drake was back and interactions with the established pair were obviously constantly happening. The unattached male was persistently attempting to approach the pair. I say 'unattached drake' because I take it that this drake is unpaired. It is possible, but from his behaviour unlikely, that he has a female incubating on a nest nearby. I say unlikely, because he does not appear to be very aggressive and that is what I would expect if he was guarding his sitting duck. It would also be very early for nesting but not impossible. However, interactions took a predictable course. The unattached drake would approach and the paired drake would react by swimming towards him and pressing him away from his female with much hostile-pumping. This hostile-pumping action takes the form of raising the head and pumping it up and down, briefly, at a steady rate. The drakes called constantly while engaged in these interactions and would close on each other twisting and turning as they swam rapidly about with an eventual rush at the intruder by the paired drake causing him to take to the wing and fly off to land on the pond about 50 or 100 m away. His flight feathers would whistle loudly with that characteristic sound of shoveler in fast flight. There would be some preening-behind-the-wing behaviour by both drakes and some wing flapping accompanied by the typical sharp cracking sounds produced by the flight feathers as they are snapped in the air and then the paired drake would swim back quickly to his female.




Confrontations between the drakes
When not engaged in these jousts the pair of shoveler spent the time, at least while I was watching and sound recording, in almost constant feeding. For most of the time Shoveler suzzle at or just below the water surface. They will upend and occasionally even dive while feeding but surface suzzling is the most common practice. This action requires that they pump a large volume of water through the bill and expel it from the sides. In doing this they are filtering the food items from the water. The bill of the shoveler is particularly well endowed with filter ridges or lamellae, especially along the margins of the massive upper part of the bill. While not as elegant nor so well co-ordinated as the action of Pink-eared Duck Malacorhynchus membranaceus a pair of Australasian Shoveler, like all other shovelers, can and often do, perform a co-operative rotating feeding method. This behaviour, which, some years ago, my colleagues and I termed 'vortexing' when we described the similar method of feeding used by Pink-eared Duck. It takes the form of a swift rotation or spinning about a central point, usually by two birds. It is likely, in fact it must be so, that they are concentrating plankton in the swirling water created by this action and the bill is constantly working the area with a massive volume of water visibly pouring out from its base. Shoveler do not do this vortexing nearly so tightly as do Pink-eared Duck but, all the same, they are clearly performing a similar action in the gathering of planktonic food. They can do it for minutes on end within a very small area. Today, I think there was a good supply of food in a certain part of the pond because the pair of shoveler returned time and again to this particular area following each of the hostile encounters. I was able to get a good bit of sound not only of the males giving their characteristic "clubit" calls but also several sequences when the female called with a repeated but rather feeble double quacking. However, without the correct windshield I was getting annoying interference from an occasional very faint breeze. It was still very cold and I always have the impression that most microphones respond rather more seriously to wind when cold. Anyway, I got some material and must return soon with more appropriate gear if his opportunity to record shoveler in particularly good conditions is not to be missed.




A pair of vortexing Australasian Shoveler


Suzzling Australasian Shoveler
Other subjects photographed at Tidbinbilla on Thursday included the now much bigger Black Swan cygnets and the Magpie Geese. The Black Swan are the same birds photographed a month ago!





Magpie Geese




Finally, some Coot attracted my attention and I must say their brilliant white snub noses give them a rather fine head profile. I must compare with European birds, and I may be wrong, but the local Coot give me the impression of more rounded culmen than occurs on birds in the western Palaeartic. Perhaps I am only imagining such a subtle difference!