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Martin,
the dates fit a 2nd brood. Pairs can initiate a 2nd
brood when the young of the 1st brood are about 3 weeks old (when they can feed
on their own). Incubation takes about 3 weeks. Young are fully independent at
eight weeks.
The young of the 1st brood may either have moved on or
are making themselves scarce. breeding adults can be aggressive. I have noticed
the "disappearance" of young from a 1st brood also, only to discover them
(more by chance) hanging out at the edge and inside vegetation etc. (see
also CBN 32 (2) 2007: 1020105).
Michael Lenz
Sent: Saturday, January 15, 2011 11:28 AM
To:
Subject: [canberrabirds] "Ageing" of Australasian
grebes
I have put quotes around the word ageing since this is whether it
is possible to estimate the age of young Australasian Grebes, rather than their
aging process. On 25 November last year I observed 1 adult and 3 young
Australasian grebes on our top dam. Some pictures from that day are in http://franmart.blogspot.com/2010/11/australasian-grebes-on-top-dam.html
Today, 15 January, I was in the area again (primarily improving some blackberry
regrowth) and found that there were still one adult and 3 young grebes: see
attached image taken on full zoom across a hazy dam.
My
expectation is that these are a second brood. Does anyone know how quickly
the chicks would grow? Is it more likely that in two months the first
brood:
- became ex-grebes (the area is well supplied with raptors and foxes are not
unknown in the area) and a second started from scratch; or
- achieved independence and departed while the excellent season (the area
around the dam is lush with vegetation full of frogs and insects) allowed the
second brood?
Martin
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