|
This is a very important conversation. The abundance of birds vs the abundance of observers is a very difficult piece of algebra for our hard-working COG statisticians to solve. I have unwittingly found myself involved in an aspect of this dilemma. In the
Blitz I reported observing both the Azure Kingfisher and the Hooded Robin. It was a bit scary to find that there is a prize for the most doubtful tick! I fear I am in the running for 1st, 2nd and possibly 3rd prize!
But there is an interesting issue here, not just whether a bird was wrongly or too hopefully IDed. The good COG folk have, quite rightly, been in contact with me to discuss these observations and I am grateful for their care and enthusiasm. Among the observations
made to me was that IF I was correct about the Hooded Robins, that would be exciting because they had not generally been reported from here before - presumably ‘here’ means Gungahlin. But I have seen them here before. I have already seen and reported them
this year prior to the Blitz but only in the GBS which COG won’t have yet. I have seen them in previous years. It’s just that I was not a member of COG until 2012. I live backing onto on Ginninderra Creek and Percival Hill and I have been actively making and
recording my own observations here for the past 13 years. I just never got around to joining COG (but I am glad I did.)
So I was interested in the recent reporting of a Black Honeyeater and the ensuing emails. I have seen those too, several times in the past 13 years, although not yet this year, not with certainty since several clear sightings in 2011, before I joined COG.
So I think the comments made about the frequency of wader species at Jerrabombera vs Lake Bathurst is cogent here. It has much to do with the frequency of observers. When I joined COG, it interested me greatly that in my grid cell, K11, only 8 record sheets
and been submitted in 2011-12, compared with well over 200 in some grid cells. It gave me a kind of motivation to change that statistic. But it does underline the truth that frequencies of the lesser-observed species are very sensitive to the number of observers
and observations in a given year. We must take care in implying that certain species are not found or not commonly found on, say, Percival Hill or even Gungahlin, if, like Lake Bathurst, the site is rarely reported on. There may be more Black Honeyeaters
than we think, given that the highest frequency of observers is in the generally older and more urban parts of the ACT which perhaps they avoid.
For what it’s worth, I have not seen the Azure Kingfisher nor the Blue-winged Parrot since the Blitz, but then I haven’t spent 3 hours on Percival Hill either, only about an hour. I continue to observe Hooded Robins.
Cheers
John
On 19 Nov 2013, at 10:14 pm, Philip Veerman <> wrote:
For what it is worth. I suspect Geoffrey's para 3 comment is spot on and Michael's is true too. In the ACT we don't get large numbers of the species that are normally common in
(coastal areas of) SE Australia. Probably because our few locations are isolated. We get small and not very different numbers of the somewhat rarer and the generally common ones.
Philip
Unfortunately I could not respond to this message from Geoffrey earlier.
In order to address the relative proportions of rarities against the 3 abundant species Geoffrey is referring to in our local fauna (Geoffrey's comment (3)), one has to keep in mind:
At Jerrabomberra wetlands any wader species (and the same applies to many other bird species) receives a lot of attention, is seen by many observers for whatever period it decides to stay, and is reported to the database multiple times over
that period. This contrasts with obs. from Lake Bathurst and Lake George during the waterbird surveys which are based as a rule on 1 visit/month.
Record summaries will have to take these different scenarios somehow into account, although I am not quite sure what the best way may be. Certainly "(No birds/visit/month (e.g. L Bathurst)" and "(average) no birds/visit/month (e.g. Jerrab.)"
may be one way of getting some idea of proportions??
Lake Bathurst was for many years after 2000 dry, hence the 8 nil years for the Curlew Sp (Geoffrey's comment (2)).
Michael Lenz
Sent: Tuesday, November 05, 2013 10:18 AM
Subject: FW: [canberrabirds] An unusual year for sandpipers
Thank you Steve. This calls for a few comments.
1) These
are records, not individual birds. (There certainly weren’t 25 Pec Sandpipers here in 2003, although there might have been 25 reports of a single bird. Similarly for the wood Sandpiper in 1994.)
2) The
NSW reports probably reflect reports by Michael Lenz from L Bathurst etc (Surprised they didn’t go back before 1981) These are remarkably consistent for the Curlew Sandpiper
up until 2000, after which there are 8 nil years. Those records appear to be cumulative (monthly) presence records, for example the ABN gives 102 Curlew Sandpipers at Lake Bathurst in October 1997.
3) I
am interested in the relative proportion of ‘rarities’ as against the 3 species that are abundant in coastal SE Australia (RN Stint, Sharp-tailed Sandpiper, Curlew Sandpiper). You can’t get this from the Michael Lenz numbers as presented here (eg 5 records
each of Sharpie and Pec Sand in 1989 gives no idea of relative numbers.) >From what we know of the ACT wetlands we seem to get a few sharpies (less than 10 at once) each year. However I think the records will show that the proportion of rarer waders here
(by number) is much higher than the proportion of rarer waders to the common 3 at somewhere like Werribee. Perhaps wader species migrating singly or in small numbers are more likely to turn up somewhere off the usual track than wader species migrating in
large numbers.
4) As
to this being an unusual year, well perhaps a combination of winds and the conditions being favourable at those local spots that get a predictably thorough scrutiny.
From: Wallaces
Sent: Monday, 4 November 2013 7:52 PM
To: Canberra birds
Subject: [canberrabirds] An unusual year for sandpipers
More reports of Pectoral and Curlew Sandpiper from Kellys Swamp today (see http://www.eremaea.com/BirdlineRecentSightings.aspx?Birdline=11)
prompted me to look at when these two species and the Wood Sandpiper have been recorded in the same year. Below is a summary of the records from the COG database. It shows that the three species have never been recorded in the same year in the ACT and only
in one year (1995) in the rest of the COG area of interest. The records for 2013 are incomplete.
Steve
|
Number of records
|
Species
|
|
|
|
State/Year ending 30 June
|
Curlew Sandpiper
|
Pectoral Sandpiper
|
Wood Sandpiper
|
|
ACT
|
6
|
25
|
11
|
|
1975
|
1
|
|
|
|
1993
|
|
|
1
|
|
1994
|
|
|
9
|
|
1995
|
|
|
1
|
|
2003
|
|
25
|
|
|
2005
|
3
|
|
|
|
2010
|
2
|
|
|
|
NSW
|
138
|
35
|
3
|
|
1981
|
1
|
|
|
|
1982
|
3
|
|
|
|
1983
|
13
|
|
|
|
1984
|
7
|
|
|
|
1985
|
8
|
|
|
|
1986
|
9
|
|
|
|
1987
|
4
|
|
|
|
1988
|
11
|
|
|
|
1989
|
5
|
5
|
|
|
1990
|
2
|
|
|
|
1991
|
7
|
|
1
|
|
1992
|
8
|
3
|
|
|
1993
|
6
|
3
|
|
|
1994
|
13
|
4
|
|
|
1995
|
13
|
3
|
1
|
|
1996
|
9
|
5
|
|
|
1997
|
2
|
2
|
|
|
1998
|
8
|
3
|
|
|
1999
|
2
|
|
|
|
2000
|
2
|
|
|
|
2006
|
3
|
2
|
|
|
2007
|
1
|
1
|
|
|
2009
|
1
|
|
|
|
2013
|
|
4
|
1
|
|
Grand Total
|
144
|
60
|
14
|
|
