Annual Report 2013: Breeding Activity

The preamble to this post is copied from last year.  That makes this report more self-contained, which I see as a Good Thing.  

It can be argued that recording breeding events is the most important aspect of bird observation since if the birds do not breed they will soon be extinct!  It is however a more difficult task than simple observation as: 

• many birds go to some lengths to conceal their nests; and
• it is necessary to be very cautious with most species to avoid frightening the birds away from the nest.

To ameliorate these problems a wide definition of breeding is employed with the core events of "nest with eggs" and "nest with young" supported by a range of other, indirect, measures of breeding activity ranging from breeding display to dependent young. (I sometimes feel that a new code is needed for "indolent young" when the Magpie chicks are clearly able to fend for themselves but would rather bludge off their parents.) To be rated as dependent young the fledglings must be

• out of the nest and generally be seen being fed by the parents or, 
• in the case of waterbirds, be incapable of flight.  

I have made an exception for the Tawny Frogmouths where the fledglings are fed at night and it isn't possible to determine how this is achieved.  In that case the young are considered dependent until they move away from the parents some 10 weeks or so after leaving the nest.

(In other countries such as Canada studies are undertaken which assume all birds seen or heard  during the breeding season are in fact breeding.)

The number of records of each type over the 7 years of the project is in the chart below.

There does not look to be any significant difference with "dependent young" dominating in both categories.  Note that this may not mean that the nest site was in the area.

Since this project commenced 563 breeding records have been noted. The decision to use the COG Breeding codes was made in late 2009 and thus approximately 1/5th of the records are not coded to type of activity.  Such is life, and the uncoded records are excluded from the above!  

A difficulty with analysis of breeding records is that the peak breeding period in the Southern Hemisphere is split by the change of calendar year.  This is illustrated in the following chart.

To overcome this I commenced, in mid 2009, recording the 'financial year" in which observations were made and it is possible from that point on to re-categorise observations to a "breeding year" (running from July to June).  It might be noted that 81% of the records after December are coded as dependent young.  The incidence of type of event x month is illustrated by this chart.

Following from this, the next section mostly covers 3 breeding seasons ending on 30 June 2013. The 2013-14 season will, inshallah, be reported on next year, but at this stage appears similar to history.

The records for 2009-10 show 58 breeding records, 2010 -11 123 breeding events ,2011-12 137 breeding events and for 2012-13 105  breeding records have been recorded. 

It is difficult to assign reasons for the drop for 2012-13 - I might try to do a separate post on this later.  In summary the following is found:

• 15 species which bred in 2012-13 had not done so in 2011-12;
• 17 species which bred in 2011-12 did not repeat the process in 2012-13.
• 5 species have the same number of reports in the two seasons;
• of the species which bred in both years with different numbers of reports,  the number of reports was greater in :
• 2011-12 in 18 cases; and 
• 2012-13 in 16 cases.

I think this resolves to an observation that breeding records are damn difficult to get.

In 2010-11 51 species were recorded as breeding while 52 species were recorded in 2011-12 and 49 in 2012-13..  These have been indicated as such in the monthly reports.  

The number of reports received over the 7 years by species is summarised in the following table.

# reports	# species
1	17
2-4	30
5-10	16
11-15	8
16+	5

As expected a large proportion of species have only been reported undertaking breeding activity a few times.  The five species with 16 or more breeding records are:

• Australian Magpie (34 reports): the swooping of defending adults and the whingeing of the dependent young are hard to ignore, however much one tries.
• Willie Wagtail (22 reports): The records for this species cover a wide range of types of "nest-centred" events, possibly reflecting the energetic distraction displays, having the unintended outcome of leading keen observers to the nest (rather than away from it).
• Tawny Frogmouth (16 reports): Once noticed the nest and parents with dependent young are easy to relocate.  Also the breeding season is 5 months long from the start of nesting to kicking the young out.
• Pied Currawong (16 reports): see Australian Magpie.
• Yellow-rumped Thornbill (16 reports): Very common species and feeding young often happens out in the open.

A couple of species dropped off the "commonest' list since last year.   Striated Pardalote possibly reflects departure of a regular observer.  Australasian Grebe is possibly affected by our top dam being deserted this year, but the nests were far less obvious around the district.  Is this an impact of the dry period after last Summer?

Links to Other Sections

Overall picture

2013 cf 2012

2013 cf previous 6 years