Monday, 18 March 2013

From my Archive - New Zealand Storm Petrel

I was intrigued to read a report on the Birdguides Webzine about the recent discovery of the breeding ground of the critically endangered, and previously thought to be extinct, New Zealand Storm Petrel. This news took me back to January 2005, when I spent an exhausting but spectacular day out in the Hauraki Gulf in search of this species, so I thought I would share some of my photos. 

New Zealand Storm Petrel - Hauraki Gulf 

The species was re-discovered by two British birdwatchers, Bob Flood and Bryan Thomas, in 2003. As I was already planning a trip to New Zealand at that time, I jumped at the opportunity to try for it. I spent 16 hours out in the Hauraki Gulf, and was able to enjoy some fantastic views of this species, and loads of others.

New Zealand Storm Petrel - Hauraki Gulf

The list included fluttering, Buller's and flesh-footed sherwaters, fairy prion, Cook's, black, and grey faced petrels. However I think the most memorable images from the trip are the views of New Zealand and white faced storm petrels. 

New Zealand Storm Petrel - Hauraki Gulf 

The most surprising thing to me about reading this article, was the length of time it has taken to find the nesting site. Here we are 10 years after the species' rediscovery and it has only just been found. I think this really demonstrates the time and dedication researchers have to put in to tracking down some of these extremely rare species.

New Zealand Storm Petrel - Hauraki Gulf

Now that the breeding grounds have been discovered I hope that the New Zealand Government makes a better job of protecting it than it is currently doing protecting Maui's dolphin.

Saturday, 16 March 2013

Ageing Siskins

Back on January 29th I reported that during a garden ringing session I had captured a male Eurasian siskin. Not a particularly notable event for some ringers, but for me this was the first siskin I had ringed in my garden since 2006. In fact, when I looked back over time I had only previously ringed 23 in my garden, two in 1998, 12 in 2003, seven in 2004 and two in 2006. 

Since ringing that first siskin of the year, I have now ringed 32 new birds which has given me the ideal opportunity to brush up on siskin ageing and here goes.

Male Siskin
Sexing siskins is really not that challenging, the male (above) has a black cap and bib, yellowish throat, upper breast and rump and heavily streaked lower flanks. The female (below) is much duller and greyer, lacking the black crown and bib and a white breast and belly which is heavily streaked. The mantle is lightly streaked and the rump whitish with light streaking in the plumage. There is very little size difference between males and females and in juvenile plumage birds cannot be sexed.

Female Siskin

Like many other passerine species adult and juvenile siskins have different moult strategies, with adults under going a complete moult post breeding, whereas juvenile birds undergo a partial post juvenile moult. However, there are always exception and Svensson states that young also occasionally undergo a complete post juvenile moult, and in Continental populations, occasionally a few primaries and all tail feathers and tertials are replaced by juveniles during their post juvenile moult.

Greater coverts of Adult male Siskin, note the colouration
and thickness of the yellow fringe of the greater coverts

Adult birds can be aged by way of the colouration and broadness of the of the outer edge of the greater coverts, and the lack of an obvious step (and contrast) between moulted and unmoulted feathers (above).

Greater coverts of First Winter male: Note the different colouration of the two
outermost greater coverts

First year birds usually show an obvious break in the greater coverts, which is evident by a difference in the length of the covert and the colouration and broadness of the fringe. The images above and below illustrate this perfectly, with the old greater coverts (OGCs) clearly visible.

Another Juvenile wing, again the three OGCs are very obvious due to different colouration and broadness of the fringe
The number of retained OGCs varied with each individual I ringed with one bird having just one and another bird having 7. Out of the 13 juvenile birds I have captured to date the average was 3.

Adult tail: Note the broad, dark and rounded tail feathers and lack of wear on the tips

Ageing birds using the tails feathers can be a useful feature, although a cautious approach should be adopted in spring when feathers can be worn. Typically and adult bird will have broad, dark and rounded tail feathers, as illustrated above.

First year tail feathers; note the pointed and worn tips

The tail feathers of first year birds are more pointed, thinner and generally not as robust and therefore they wear more quickly. The image above illustrates the shape and condition of the tail feathers of one first year bird, whereas the image below illustrates another. Note the difference in the colouration and the extent of wear on the tail tips on the image above but not the one below.

First year tail: Note the feathers are still pointed but are not heavily abraded as with the bird above

It does pay to be cautious with tail feathers in isolation though, for example the image below illustrates what looks like an adult type tail. The tips of the feathers are generally rounded, the feathers are broad and dark in colouration. But this bird had three retained greater coverts in the wing and therefore, given the species' moult strategy, must be a first year bird. The presumption with this bird is that it has either lost its tail and replaced it, or it has simply moulted its tail, as has been shown to occur in some Continental populations. In fact maybe it was a Continental bird!

Tail of first year bird: This bird had three OGCs in the wing
and therefore must be a first year, yet the tail looks distinctly  adult like.

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