Sunday, 11 January 2009

Too many spoonbills are never enough

This post is primarily intended for people interested in the breeding of Royal Spoonbills in the Jerrabombera Wetlands, specifically Kelly's Swamp, in Fyshwick, ACT. It is an initial sequel (or possibly a presequel) to an article I wrote for Canberra Bird Notes (CBN - published by the Canberra Ornithologists Group (COG)) which covered the first few weeks of this event.

I expect that a more thorough discussion of the later stages of the event will be published in the June 2009 edition of CBN, but thought it would be useful to summarise matters a bit closer to the event. While I have used my own images, such as they are, here I have also included some - several orders of magnitude better -very kindly offered by Geoffrey Dabb where noted below. He has also offered to give me some others for the published paper.

For the benefit of those who don't have access to CBN the image to the left shows which nest is which in my terminology.

The entire event began to be observed (I suspect the very first stages of the event - courtship of the birds from the LH nest - went un-noticed) on 25 October 2008. I have ruled a line under it as at 26 January 2009, when a chick flew out of the Upper nest. Over the intervening period period many members of COG have contributed observations of the birds at the nests and its surrounds, but I would particularly mention the contributions of Geoffrey Dabb, Frank Antram and Elizabeth Compston who were regular visitors to the hide (blind, for North American readers) overlooking the site.

I will also remedy an oversight in my previous CBN article by acknowledging the late Delia Johnson, who reported the first breeding record for the ACT in February 1998.

In the 2008-09 event it was difficult to see into the nests although the builders of Cygnus hide are to be congratulated on their foresight in its placement many years ago. On the basis of what was reported the following summary is offered:
  • three nests were commenced and all fledged young. That is a very high success rate compared to the literature cited in the Handbook of Australian, New Zealand and Antarctic Birds (HANZAB);
  • the LH nest hatched 3 chicks, RH nest 2 chicks (but visibility into this nest was particularly poor), and the Upper nest 4 chicks - thus total chicks hatched 9;
  • in terms of fledging - defined by me as a chick flying from the nest tree - the outcome was LH 2 chicks and RH and Upper nests 1 chick each;
This photograph by Geoffrey Dabb shows one of the chicks (N1Ja or b) from the LH nest soliciting food from its proud parent. It is probably capable of feeding by itself but still gets a little help.

  • Some rates are thus -> an average 1.3r chicks per nest, and 0.44r chicks fledged per chick hatched.
I suggest readers click on the Gantt Chart image above, and obtain a full size image (if that is how their email browser works), should they wish to read the labels. While I do realise that some birders have good enough eyesight, I don't think even a raptor specialist could read them as is. They may also wish to do the same with the following image, showing the 3 chicks from the lower nests playing in the water!

The issues which I hope to canvass in further detail in the forthcoming article include:
  • the differing durations of the stages of development in the various nests, including a comparison of the observed events with the material in HANZAB (noting that HANZAB has very little information on the duration of post-hatching events);
  • the various definitions of 'fledging' and how they apply to this event; and
  • interactions between the spoonbills and Australian White Ibis during later stages of the event. I might also use Ibises as a proxy for commentary about growth rates of the Spoonbill chicks. (The image above gives an idea of the number of ibises hanging out in the nest tree in the later stages of the breeding event.)
The final image is by Geoffrey Dabb and shows the event which concluded this data gathering exercise. That is, the chick (designated N3j) launching itself from the tree for the first time.

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