yfhes

["Harvey Perkins" <>]

I agree wholeheartedly, Martin, discussion on this is good...

 

In my previous response I was referring to Chris's suggestion that the same birds return to the same areas each year - not any change in magnitude of the migration this year. The GBS data can certainly be analysed and used to compare this year to others in terms of magnitude, timing etc, but it provides absolutely nothing in terms of whether they are the same birds or not. Personally I'd love to think that that is the case but there is no evidence.

 

Surely the poor conditions in the ranges (if that is where we are talking about as the source for our autumn migration birds) as a rusult of 'recent' (note Philip's comments) bushfires would affect breeding success and migration numbers whether they were the same or different birds using the area. It is unfortunate that Steve Wilson's massive long-term banding effort with YFHEs returned essentially no information in terms of birds returning to the same areas.

 

Harvey

 

On 03/05/07, martin butterfield <> wrote:

The discussion raises an interesting point.  I agree that it is not possible, on the evidence presented, to make any rigorous judgements about the magnitude of the YFHE migration or the cause of any changes that might eventually be detected. 

 

However by flagging the possibility that there has been a change, the discussion should have started the analysts in the readership pondering how they could use the GBS data for this year (when it becomes available later in the year) to investigate whether there has been a change or not.  If no-one advances the possibility it is less likely that someone will do the necessary investigation.

 

Of course even when this year's data is available it can at best provide only partial data.  Another 2 or 3 years of information would be needed to confirm any hypotheses.

 

Martin

 

On 5/3/07, Harvey Perkins <m("gmail.com","hdpphd");" target="_blank">> wrote:

On 02/05/07, Philip Veerman <m("pcug.org.au","pveerman");" target="_blank"> > wrote:

Hi Chris & All,

You could very easily be right, however that is a big "if" in your last paragraph. We are a long way short of being able to say "This, ...is the first time that this has been shown."

 

 

I have to concur with Philip on this one. While the observations are interesting, the conclusion is based on very little hard evidence. Also, the migration this year seems to have been atypical in that there was a fair bit of movement in early and mid March I think it was, which might/would have impacted on the numbers moving in mid April...

 

Harvey