Wednesday, 29 April 2015

Jaegers: Hunting For Answers

With so many jaegers up close and personal we have had a better opportunity to study them than unusual. All of the Pomarine Jaegers (25-27 in total) have been light morph adults, and all but one have been in breeding plumage (one appears to be hanging onto it's winter plumage). And there have been 4 Parasitic Jaegers. Plus 3 jaegers seen in St. Pierre!

Lots of wondering as to why this event has occurred. Nothing like this has happened before in Newfoundland. The wind wasn't exceptionally strong, and fog certainly isn't unusual so it makes sense that a lack of food became the prime suspect to explain the event.

A message from Yann Kolbeinsson (birder in Iceland) to Jared Clarke gives more perspective on the event. He suggested that events like this are more regular/expected in Iceland. They occur with moderate onshore winds with humid foggy air, and rain. This type of event has previously occurred in Iceland in the first to second week of May.


But, that kind of weather is more or less the norm here! Perhaps the difference this year was the far-reaching Easterly winds, at the right time of year (bringing migrating jaegers from the open ocean closer to our waters)? Maybe a poor food supply exasperated the meagre weather, causing them to be stranded on our shores? All questions that we simply don't have concrete answers to. If it happens again another year, maybe then we can connect the dots.

Which is a great segway into eBird! eBird is the perfect medium to document an event like this - it gives a temporal and spatial perspective on the event, and the data is saved for future generations!

Here's a quick map of all the Pomarine Jaeger sightings in the last couple weeks:

See the link here for the up to date map





Despite all the Pomarine Jaegers being light morphs, there has been a bit of variation of their plumage. Mostly in the breast band.

Some have a complete breast band:



Others have close to none:



Others have a more diffuse breast band:

On the Pomarine Jaeger above, note that the black cap extends all the way down to below the gape of the bill. Compare that with this Parasitic Jaeger:

Note that the black cap clearly ends at the gape of the bill - the area below the gape is slightly darker than the neck, but is noticeably lighter than the cap.


One Pomarine Jaeger stood out from the rest due to the extensive dark markings on the chest:



My thought was that this was because it was still partly in non-breeding plumage rather than being a sub-adult. Something to look up when I have more time another day!


This photo was taken by Ken Knowles (same bird showing the extensive chest markings).




Two Parasitic Jaegers showed up at the St. John's harbour.

I am calling this Parasitic Jaeger an "intermediate morph" because it doesn't seem as light as the Pomarine Jaegers that we've seen this week.


Also because I have seen a lighter adult Parasitic Jaeger in the Northwest Territories - as seen here with its mate, a dark-morph Parasitic Jaeger!
Perhaps their offspring would have looked similar to our intermediate morph in St. John's?



Jaeger sightings are always exciting, but are often frustrating because they're difficult to identify when seen out over the open ocean. It's been no problem identifying them this week while they're stranded on our shores - but they still bring a lot of questions and confusion with them.



POJA:

PAJA:



This female Northern Pintail was acting "nesty" in St. John's earlier this week:

3 comments:

  1. Hi Alvan:

    based on the underside being white rather than the having the dark markings cover the underside of the Pom in question I agree with you that this bird from Witless bay was in non-breeding plumage. I had originally thought this bird was a juvenile but now believe that is incorrect. None of your photos shows the underside of the bird which is necessary. Here is a link to a photo I took that shows that the dark markings are only on the upper chest, the rest of the chest and underside are white.
    https://www.flickr.com/photos/geneherz/17301956462/

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  2. This comment has been removed by the author.

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  3. Sorry, I don't know how to make the link in my message above active so you will have to copy and paste the link into your browser. Feel free to use the image if it is helpful to the discussion

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