canberrabirds

Common Myna Breeding, and recording breeding of any species.

To: "martin butterfield" <>, "Esme Barker & Bruce Ramsay" <>
Subject: Common Myna Breeding, and recording breeding of any species.
From: "Philip Veerman" <>
Date: Sun, 24 Jun 2007 16:51:21 +1000
Hi All,
 
The GBS is an important data source and it matters that interpretation is properly understood. The graph that Martin provided presumably shows the number of breeding observations combined, of all types, by week. That has peripheral usefulness. However the benefit of the GBS Report graph is that it shows (in a separate graph for 18 species) the total, divided into the three main phases of breeding, being: 1) pre-laying, 2) incubation and nestling periods and 3) fledgling and dependent young periods. This is shown by month and number of breeding observations, importantly divided by the number of observer weeks in the month, this gives a true ratio, rather than just presenting raw counts. Raw counts are very skewed by variations in the number of observer weeks over the year. This is proved by the dip in the middle of Martin's graph, which is totally due to the fact that many observers are away in the last week of December (as shown in Figure 6 of the GBS Report), and nothing whatever to do with the birds' behaviour.
 
As for the comment: "there is not a single CO record in the database for this species.  Clearly they appreciate their privacy!" The conclusion, whilst presumably offered in humour, does not demonstrate an understanding of the real reason. The GBS Report gives the history. Which is: after my review of the GBS in 1988-90, I and the records group of COG instituted the instruction to include the new set of breeding codes, with Version 3 of the chart in 1993. This was to match the new codes that the COG records system had developed and bring both into line. Before 1993 there is not likely to be any co obs for any species (because the code was not listed as an option). More importantly, the instructions say: "Record any breeding with the first applicable of any of the following codes: ny; nest with young, ne; nest with eggs, fs; faecal sac, on; bird on or seen leaving nest, nb; nest building, cf; carrying food, dy; dependent young, ih; inspecting hollow, di; display, co; copulation, or keep a separate list."  Note that "the first applicable" is instructed and that co is the last given option. This sequence is not random, it was carefully thought through, to give strongest weight to evidence that indicates that breeding is actually occurring (preferably locally). Seeing birds copulate, is not of itself, terribly strong evidence of local breeding, in contrast say, to nest with young, that is definite evidence both of time and location. Nest with young is listed before nest with eggs because it is evidence and that it has moved one step closer to success than nest with eggs. Likewise the reason dy is not listed first (indicating success) is that it does not, of itself, show that the nest was within the GBS area. That is why there is not a lot of co observations for any species (being listed last). The space available in the little boxes on the chart is limited. Observers should record the most definitive evidence of local breeding that is available. It has more to do with intelligent design of the instructions on the chart than that the birds mynas or anyone else appreciate their privacy!  
 
As a last comment, Martin also wrote: "I have trawled the breeding records in the GBS database". I mention, that because of the way I designed the GBS database, it should take about 1 minute for someone to output that information.
 
Philip
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