Monday 8 August 2016

Cory's Shearwater invading Newfoundland Waters?

Last Saturday during a 2-hour seawatch at Long Point I watched as a large shearwater sailed South with a group of Great Shearwaters. It had all the markings of a Cory's Shearwater - no collar, dusky facial markings that extended down below the eye into the cheek, and lacked any sign of a white rump. But the range of Cory's Shearwater doesn't extend into the St. Lawrence and seeing them from a headland is extremely rare from the best of locations (in fact there's only 1 previous land based record for the island). So I dismissed that bird as a "shearwater sp." and vowed to study my Great Shearwaters more closely.

The next day while waiting for a ferry to cross the Cabot Strait to Nova Scotia I did a 1-hour seawatch from Cape Ray. Within the first 5 minutes I had another shearwater that looked perfect for Cory's. At this point I thought I was going crazy and clearly didn't know my local shearwaters (there's only 3 local species!) So I hit the books for 10 minutes and reviewed all the information available to me. Sure enough, 10 minutes back into the seawatch another perfect Cory's Shearwater sailed by with a Great Shearwater. It was close enough for me to feel confident in the ID but without a photo I felt a little hesitant because I knew the veterans would doubt the sighting.

Then the ferry crossing started. We left dock just before noon and arrived in Sydney just over 6 hours later. As soon as we got out of the harbour I was seeing small numbers of shearwaters - for the next 6 hours there was almost always a handful of shearwaters within view. Conditions were perfect with cloudy sky (= no sun glare), very little wind (= no white caps, and easy to stand outside on the side of the large ship).

About an hour into the seawatch I resorted to doing 10 minute counts of the seabirds. I tallied numbers for each species within the ten minute period and restarted the count again every 10 minutes. My final count for Cory's Shearwater was 41! This is an unprecedented number for Newfoundland waters. To add to this, Bruce Mactavish is currently 350km East of St. John's where he has seen 14+ Cory's in the last few days - an area he has visited for several years on job assignments and has never seen Cory's before.

For some context: most of the veteran Newfoundland birders have not seen Cory's Shearwater for their Newfoundland list!

Here are some photos of Cory's from the ferry crossing:

Any theories that might explain this unprecedented incursion of this species?

Obviously warming waters could be one explanation. But water temperatures on the Eastern Grand Banks are not above recent averages and I don't know what they are like off Nova Scotia.

Great Shearwaters from the ferry:

The three regular species of shearwater visible from Newfoundland headlands:

Sooty Shearwater - all dark bird, with long stiff wings:

Great Shearwater - the largest of the 3 regular species. Flight not nearly as "stiff". And white underside often visible from great distances.

Manx - the smallest of the three. Can be identified from great distances despite small size due to the very stiff flight pattern with short wings, white undersides, and the relatively small size.

Lots of things I want to write about but absolutely crushed for time right now.