Thursday, January 4, 2018

Annual Report Breeding Birds

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 some wide definitions of breeding are employed with the core events of "nest with eggs" and "nest with young" supported by a range of other, indirect, measures of breeding activity.  

In the case of the Canberra Ornithologists Group the traditional values 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 International eBird project, run out of the prestigious Ornithology Programme at Cornell U in New York takes a very broad view with 22 codes including indirct codes such as “Singing male” (Possible breeding) and “Agitated Behaviour” (Probable breeding).  Of course, with this wide set it is possible to choose and I shall stick with the set of traditional codes used by COG for this project.  (As over 50% of COG General records are now sourced through eBird there must be some careful filtering done to map between the two systems.)

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 (covering all 11 years of the project - it is very similar in shape to earlier years.
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).  

Since this project commenced 1004 breeding records have been noted. (i think the 1000th record was a Laughing Kookaburra.)  The decision to use the COG Breeding codes was made in late 2009 and thus approximately 12% of the records are not coded to type of activity.  Such is life, and the uncoded records are excluded from the next chart!  

The percentage of records of each type is shown separately for the last complete 'season (2016-17) and the rest of the records in the chart below.

There is not a significantly different distribution of type of activity reported in 2015-16 and the rest of the series.  The preponderance of dependent young (code 'dy') records reflects both the relative ease of observing this and the duration of the phase - for some species this can go on for several months. It is recognised that the begging young could have been hatched out of the area.  (Of course finding a nest with young does not necessarily mean the young survive to maintain the species: we have plenty of Pied Currawongs in the area to predate nests and fledglings.)

It might be noted that 87.5% of the records after December which have been coded to type of activity are dependent young. There have been several records of active pardalote, honeyeater and finch nests in the New Year.  In most cases these are presumably second broods, although the Noisy Friarbirds which nest at our place are known to be late starters.
 The incidence of type of event x month is illustrated by this chart in which the redder fill indicates a greater number of records).  Some codes have been grouped to combine the less regularly reported ones.
Following from this, the next section mostly covers 7 breeding seasons ending on 30 June 2017. The 2016-17 season will, inshallah, be reported on next year, but at this stage appears similar to history.
Breeding season# breeding records
It is difficult to assign reasons for the differences shown in this table - I might try to do a separate post on this later, when feeling particularly masochistic.

Taking the number of species seen in each season the following result is obtained.  

Breeding season# breeding species
In past years my impression was that the number of breeding species is a little more stable that the number of breeding records.  However the very low number of breeding species in 2014-15 argues against that.  I can't at this stage offer an explanation for this, but will try to ponder the issue later.

The number of reports by species received over the 11 calendar years by species is summarised in the following table.
# reports
# species
As expected a large proportion of species have only been reported undertaking breeding activity a few times.  The 17 species with 20 or more breeding records are:
  • Australian Magpie (74 reports): the swooping of defending adults and the whingeing of the dependent young are hard to ignore, however much one tries.  That being said no-one reported breeding behaviour by  Magpie in 2013-14 - I didn't even get swooped riding my bike!  The situation has returned to normal since!
  • Tawny Frogmouth (47 reports): Reports from several observers this year.  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.  
  • Striated Pardalote (46 reports): a serial offender at building a nest in any apparent hole in a building or tree.  Reports from several observers this year. Also very vocal when doing so! 
  • Pied Currawong (42 reports): see Australian Magpie.  In past years there was no way I could miss the {expletives deleted, with regret} pair that nested above our lawn and swoop me every time I walk across it!  For calendar 2016 and 2017 they moved nest site by 30m and were much much more sociable.
  • Welcome Swallow (36 reports):  Nest building is very obvious as they prefer a site such as in the rafters of a shed.  
  • Willie Wagtail (33 reports): Only a single record for 2016-17.  in past years 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).  
  • Australian Wood Duck (32 reports)  A very common bird around farm dams and lawns, in Spring often leading a conga line of ducklings from the nest in tree hollows.
  • Australasian Grebe (30 reports)  They no longer nest on our top dam but  I have received a few more reports from other observers so they have made the big league.  The young birds are particularly interesting with striped heads.
  • White-browed Scrubwren (28 reports)  A very active bird and repeated zooming into a bush with a mouthful of grubs attracts attention.
  • Grey Shrike-thrush (27 reports): this species often nests in sheds or on verandahs, so is easy to spot.  Several observers reportedThey also fit in more than one brood so get several reports per site-year.
  • Yellow-rumped Thornbill (24 reports): Very common species and feeding young often happens out in the open.
  • Yellow-faced Honeyeater (23 reports): this species appears very relaxed about building close to dwellings - although in our case in our case the rose bush used in past years was burnt out.  So relatively easy to find and monitor the nest.
  • Common Starling (23 reports):  Frequently seen entering a hollow with a beak full of grubs!  Sometimes competes with parrots and cockatoos for use of hollows.
  • White-faced Heron (20 reports): A large and common bird which makes a large smelly nest, often quite a distance from water.
  • Superb Fairywren (20 reports): Very common bird often seen feeding young.
  • Red Wattlebird (20 reports): a large bird with very noisy fledglings.  No breeding records in 2016-17 although the species continues to be seen.

Links to other sections of this report

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