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Fea's Petrel - Cape Verde (off Sao Nicolau) - April 2013 (1 Viewer)

Paul Chapman

Well-known member

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A couple of articles to read to answer the question - what taxon(s) do we get?

All the best

Paul
 

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A couple of articles to read to answer the question - what taxon(s) do we get?

All the best

Paul

Ok Paul, I'm going to play the game. Having seen Desertas off Desertas in July I am fairly sure I have seen Desertas.

The whole rest of the information seems to be based upon conjecture. I am not doubting anything that has been written but logically the arguments are hypothesis that remain to be proven.

You say that you know that your photos from Cape Verde are Fea's. Yet the text says that Desertas in non-breeding range to Cape Verde. Did you identify on range, and if so how can anyone separate non-breeding wandering Desertas from 'resident' Fea's?

If for breeding, as suggested, Desertas is closely placed to Desertas/Madeira, why do we get a peak of records from sea watching in August/September. They shouldn't be there - unless these are non-breeding birds perhaps? (is this just a reflection of observer activity rather than number of birds?)

What do we know of the development of plumage and size. We know they are sexually dimorphic and there is overlap in size and bulk between species but can anyone sex birds in the field (or should I say rocking boat?). What about ageing birds?

It feels to me that this is one of the great ID challenges at the moment (up there with Band-rumped/Madeiran Storm Petrel - I gave up off Hatteras with Patteson crew - there were definitely differences but no idea what they meant).

The text suggests we should get Zino's - has anyone claimed one yet? All photos I have seen have the thick bill and heavy appearance of the Desertas/Fea's pair.
 
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Thank you very much for coming to play. I hoped someone would! :t:

Just to say, I'll look tonight as I am at work currently.

(I've changed my mind on these several times as to what I think is most likely....)

All the best
 
In answer quickly to your points:-

1. The Fea’s Petrels were solely identified on range so probability. As you indicate, the last week of April is within the breeding period of Fea’s Petrel (population 500 pairs) and right at the end of the non-breeding period for Desertas Petrel (160-180 pairs). So whilst Desertas Petrel does occur in the Cape Verdes outside the breeding season, surely the combination of timing and population size makes it a very strong probability that they are Fea’s Petrels. Indeed, that would be the case even if the entire Desertas Petrel population was in the Cape Verdes at the time.

2. I think to speculate on what is the most likely taxon in British & Irish waters, you need to combine the following:-
(i) Population size – with populations of Fea’s (500 pairs), Desertas (160-180 pairs) & Zino’s (65-80 pairs), this would indicate Fea’s Petrel on size of population.
(ii) Distributions – however, Fea’s Petrel (4,000km) would need to travel twice as far as Desertas or Zino’s Petrels (2,000km) so that would suggest Desertas or Zino’s Petrel on distance travelled.
(iii) Known movements – this is where the data logger information which suggests that Fea’s do no travel much but Desertas & Zino’s do is interesting. However, as only one Fea’s Petrel chick was recaptured as an adult and the proportion of the population sampled was the smallest, surely that is of limited use? The fact that Desertas & Zino’s travel to the south Atlantic, eastern seaboard, etc with such small populations, makes them thin spread doesn’t it? So I do not really buy the theory that this study suggests Desertas & Zino’s Petrel are more likely vagrants for us than Fea’s Petrel.
(iv) Plumage/morphology – as you point out, the size of the birds, their structure and the bill means almost all are Fea’s or Desertas Petrels. The fact that there few if any birds with massive bills suggests to me that they are not adult males certainly. I chatted to the late Jimmy Steele (whilst seawatching at Newbiggin) about the two I have seen well from boats in British & Irish waters. Both conformed totally to his British Birds article.
(v) Time of year – for me the August/September peak suggests that the majority of our birds are young Fea’s Petrels. As you say, non-breeding Desertas could be the source (or even extreme foraging trips), but I favour Fea's. I doubt that observer bias is that important. Sea temperature could also play a part in the August/September peak. Wouldn’t that mean birds wandering at that time of year may wander further into our waters?

3. Struggling to find my references this evening, but surely the significant differences in size and bill make sexing in the field possible (from boats) and surely as well bill sizes increase with age (whereas overall size of the bird is pretty much fixed on fledging). I was interested by the size variation of the bills of the Bulwer’s Petrels, I saw on Madeira and assumed that this was age-related if not also related to sex.

4. I don’t know If moult or plumage could ever be useful?

5. I know of one claim of Zino’s.

On balance, I think all three taxa could occur but personally, I think that we most likely get Fea’s Petrels……….

All the best
 
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It was largely thought that the recent Irish bird was probably Desertas

Sam

Sam

I remember seeing some tweets referring to Desertas (or Fea's) - so shorthand for either/or. I don't recall it being 'uniquely brutish' as the Bob Flood article refers to some Desertas.

Any links?

All the best

Paul
 

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I am not getting 'uniquely brutish'. From memory, the closest to 'uniquely brutish' that I have seen is Scilly on 19 August 2014:-

I am getting the same 'feel' but this is meaningless as it is not a clear differentiator except for the largest of male desertas.

Not to quibble with your photographic skills but the photos of the birds Paul has posted cannot really show what is necessary. Looking at the underwing patterns there is a paper from Shirahai that shows wider variability than suggested and I read somewhere an article about the search for birds with all white underwings that have been seen - can't recall the reference at the moment. It is worth looking at the Madeiran Windbirds website for photos as the trip report pictures have improved massively over recent years. I dont know where to look for similar quality photos from Cape Verde.

It is also worth looking at Patteson's blog pages. They see "feas" off NC and their trip to Madeira made interesting reading - even if most of it was about their view of Band-rumped storm petrels. They spend so much time with the birds that their view point is most relevant.

The numbers game is also not necessarily relevant - it is arguable that if Fea's were present then 50 times as many Cape Verde Shearwaters should be seen in British waters.

The prevalence of suitable wind & currents could give a clue. Most of the birds are feeding either in the North Atlantic Conveyor (Gulf stream) or on the break between this and other ocean waters. Once on a favourable wind, 1000 km could represent less than a days travel and with minimal energy expenditure. It is known (believed) that there is interchange of feas/desertas between CV and Madeira so a skip into the stronger SW-NE system means the UK is not far for either species.

I believe to answer the questions - we need to understand more about the species habits and also try and understand if they are separable at sea. At the moment we dont appear to know enough to say if they are one species or another.
 
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