Balearic Shearwaters through west Lyme Bay, 2017 a good year?

While seawatching at Berry Head recently I was asked what 2017 was looking like for Balearic Shearwaters off South Devon? I've been keeping a study going of numbers through west Lyme Bay while seawatching either Berry Head or Start Point for a few years now. So what's 2017 looking like?  So far June-September 2017 I've logged 1060 birds in 146 hours watching. So taking into account effort that's 7.3 birds/hour (the best measure for comparison). This is much better than last year's 2.7 birds/hour, but there has been better. As a comparison of years I take the period June–November, which captures the majority WLB Balearic passage (so there will be data to add to this year, which may push the rate higher or lower). See the graph below:

As you can see so far 2017 is looking above average (mean for all years based on data so far is 4.5 birds/hr), but not matching the years 2011, 2013 and 2015; unless we get a big late surge, which is possible. Also we might not get any more big numbers and the 2017 rate will come down. What 2017 has showed so far was a big peak in the period from late July to early August and had my best July passage day of 185 birds on 28th. The best day so far was  3rd August with 203.  So far there have been five three-figure counts and the general trend has been more birds moving through outer Lyme Bay - so bigger numbers at Start rather than Berry Head.

4 comments:

  1. Hi Mark, another fascinating blog post. I just wondered what your view is on counts during feeding circuits as apposed to proper movements of Balearics. Sites like Berry Head and Portland Bill can have large 'movements' of Balearics when other watch points don't, which for me indicates it isn't actually a movement but more a food thing. Could this mean true numbers are hard to asses on some occasions as they may well involve multiple sightings of the same individuals? Even during the same day, but surely without a doubt within consecutive days. Have you ever had proper evidence of this happening? Like a leucistic or strikingly plumaged bird which is identifiable as an individual.

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    1. Hi Steve, very good point. There is almost certainly going to be some circulation of birds, especially if a good food source and/or very windy. This was particularly evident in 2011 when many Balearics were feeding (circulating) in inner Lyme Bay (see DBR2011 p.50 as an attempt at an explanation). Circulation could be at local scale, e.g. within a few miles of BHd (and I'm sure this happens at Portland which is a very good feeding area from 'at sea' surveys),or over a larger area like outer Lyme Bay, or even within the E channel itself. But many birds are also moving through. Due to the position of the WLB sites, they are better placed to pick up passage which is generally W or SW and usually fits in when big numbers are off the French coast (I did a write-up on this in Brit Birds 109:350-352). But in answer to your question, no I've not seen a really distinctive Balearic off BHd or SPt to check this out, we really need one with GPS/logger to really see what's happening. Researchers have put loggers on breeding birds, but this has shown they are not coming this far up, therefore we are generally seeing the non-breeders! Males and females were also showing a preference for different areas!
      I do think SPt picks up the best shearwater passage as it sticks out further into the channel - usually getting more of all shearwater species compared to BHd or inner Lyme Bay sites, unless very windy (S-SSW)and birds have been driven up there (and are circulating due to the wind?!) and of course SPt becomes difficult to watch in such conditions.
      I do think the lingering / circulating effect is even more pronounced with skuas in Lyme Bay, and one year I did see one distinctive plumage Arctic on 3 different days from BHd! SPt never gets BHd's skua or tern numbers and then BHd never gets inner Lyme Bay's Sandwich terns! All this makes seawatching so fascinating.
      All we can do is keep recording in a systematic way (numbers, direction, watch period etc) and try and unravel some of these mysteries.

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    2. Fascinating reply thanks Mark - it is really such an unknown! Love the Skua tale, but I suppose Skuas are very likely to stick about if there's plenty of food. With Balearics reporting it as you have with birds/hour is a great idea as duplication irrelevant. With total numbers though I reckon it could really muddy the waters, a year with a couple of excellent Balearic passages but poor general feeding conditions could give a much lower total than the annual total of a year with excellent feeding conditions which actually involve far fewer birds.

      Sea watching of Seaton is an absolute nightmare in a straight southerly, as we are one a fairly east-west bit of coast birds don't know which way to go so duplication a real issue! At least if there's a bit of east they mostly fly east, and the opposite with a bit of west. SW our best wind direction by a mile.

      Keep up the great posts!

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    3. Hi Steve, it could. But its a good sample size. An average of 173hrs a year (so its not just a couple of days which could give an atypical result). I'd say this year is mostly passage (apart from yesterday 10/09/17). Just updated graph and figures. Off to Pendeen now again! Cheers

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