Thursday, 22 August 2013

The Tawny Frogmouths are at it again!

The Tawny Frogmouths which allow us to share their territory have started breeding again.  The first indicator of this was the appearance, on 21 August of a few twigs in their old nest site in a Yellow Box (Eucalyptus meliodora), used from 2008 - 2010.  For 2011-12 they used a different site in a Red Stringybark (E. macrorhyncha) some 70m West of the Box.

About 2115 in the evening of the 21st I saw a Froggie land on the lawn and fly up into the Box.  As the lawn is well endowed with twigs, I assume it was gathering twigs for the nest.  By the next morning the nest was substantially bigger.
It is just possible to pick out a layer of leafy material rimming the pile of twigs.

It is notable that this is 2 weeks after a researcher undertaking a long term study of many pairs of Frogmouths in Canberra reported the start of nest-building by his birds.  This continues the stream of evidence of things in Carwoola trailing those in Canberra by two weeks, and supporting observation of events lagging by 1 week per 100m elevation change.

A comment has been made that there could be a lot of variation of the altitude of breeding and feeding zones.  HANZAB suggests that territories could be as small as 20Ha or perhaps as large as 80Ha.  With this pair, their roosts sites for 9 months of the year are usually within a 2 Ha area, and I have come across other Frogmouths within 500m of the nest sites.  A circle of 500m radius has an area of ~80Ha, while one of 250m radius is ~20Ha!  Within either of those circles on our property, or those adjoining, elevation would only be +/-30m of thse of the nest trees.

Looking back over the 6 years for which I have been following the birds, the dates of starting nest building and brooding are shown in this Chart.

The top of  the rainbow areas reflect events in which the apex of the bar is the date I actually observed the start of the event, while the top of the monochrome area is the date on which I believe, from the duration of activities in later years, the event actually started.  If that theory is correct the male should start brooding about 15 days from the start of nest building (ie about 4 September).

There have been two major changes in behaviour this year compared (particularly) to 2012.  These relate to where the birds have roosted during the day and the proportion of days in which I have been able to locate them.

Locating Daytime roosts
I take whether I am able to find the male bird as an indicator on success in location.  (There have been very few occasions on which I have found the female and not the male.)  The following table shows the percentage of days in which I was home and unable to find the bird.

Month 2013 % not found 2012 % not found 2011 % not found
Jan-13 87.10 87.10 96.77
Feb-13 82.14 65.52 71.43
Mar-13 50.00 19.35 48.39
Apr-13 7.14 12.50 20.00
May-13 0.00 37.93 18.52
Jun-13 0.00 36.67 10.00
Jul-13 0.00 0.00 4.35
Aug-13 0.00 0.00 3.23
3.57 0.00
0.00 0.00
30.00 22.22
64.52 25.81

They were clearly very difficult to locate after the 2012 breeding event but were much easier to locate in May and June this year.

Choice of Daytime roost site
In the following chart I have shown the percentage of days, between March 1 and August 21 each year on which each daytime roost site was used by the male bird.  (I have excluded the days of which I was absent or couldn't find the male bird: as they are together ~90% of the time this effectively means i couldn't find either of them.)
Key elements are illustrated in this snip from Google Earth.

The two "high-use" sites from 2012 barely used in 2013 (shown as 'A')are both close to the nest site used in 2011 and 2012 (flagged '2').  The two sites used heavily in 2013 and much less in 2012 (noted 'B') are both close to the nest site being used this year (flagged '1').  In particular the site I call "Favourite roost" - the upper of the B's - was only used 4 times in 2012 against 36 times this year.  (I call it "Favourite roost " as it was the site I most commonly found them in 2009-2010, when I really commenced the rigorous daily searches.

I have no idea what this means in terms of the bird's behaviour.  Some research and contemplation is in order.

Regularity of elapsed time
My records include, with varying levels of detail depending upon what the birds have done, some interesting insights into the length of components of the breeding cycle.

  • 1n 2010 there were 16 days between the first twigs being laid in the nest and brooding commencing.  In 2012 the equivalent elapsed time was 14 days. 
  • For the years 2009-12 the length of period from start of brooding to chicks leaving the nest permanently has been 61, 63, 61 and 61 days.
  • For 2010 -12 the time from the male displaying agitation on the nest (which I believe to suggest hatching is going on under him) to chicks leaving the nest has been 34, 33 and 33 days.

WRT the male "showing agitation" this only occurs for one or two days.  When sitting on eggs he is motionless unless a Currawong requires looking at. Once the chicks are out of the egg he seems to sit still while they shuffle about underneath him.  Each time he has been restless the fluffballs have appeared about 4 days later.

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