Thursday, October 24, 2019

October 18, 2019 - Diablotin - by Kate Sutherland

Our last offshore excursions were in late August, the September trips were cancelled due to Hurricane Dorian and uncertainty about when Hatteras village would be open to visitors.  So we were looking forward to getting offshore last week for our annual October outing! 
Winds were strong from the west for a day or two preceding our scheduled trip, but due to shift around more to the north west and fall out a little on Friday.  Satellite images showed a nice temperature break to the south of us, so that is what we set our sights on that morning!  On our way out to the shelf break we found a nice flock of Cory's Shearwaters, with at least one Scopoli's and one Great, feeding over a school of false albacore.

October is a nice month to get offshore here because you just never know what you might turn up in the blue water.  But one species we do know that we should find is Black-capped Petrel.  And in October they are fresh plumaged and striking, not to mention excellent for photographing (Kate Sutherland). 
Just over the shelf break the water started warming up, but it was not the clear, deep blue of the Gulf Stream quite yet.  Regardless, Black-capped Petrels caught the scent of our chum and came to us directly.  In less than thirty minutes we had nineteen around us, then twenty-five, our maximum count was twenty-eight!  Great Shearwaters also responded well to the chum and stayed with us for most of our time out in the deep (Kate Sutherland). 
Audubon's Shearwaters were out there, but difficult to see as they flew close to the water in fairly steep waves.  A couple came to feed in the slick, so at least everyone had a chance to see the species well!  Wilson's Storm-Petrels were out there too, but just a handful were seen over the course of the day.  Just before we began heading back toward the shelf break a Pomarine Jaeger came in to investigate our following flock, but it did not chase or harass our shearwaters as we sometimes see.  Instead, it was happy to settle in and feed alongside of them, an interesting combination! (Peter Flood)
The Black-capped Petrels were, however, unimpressed with the seemingly kind jaeger and dogged it a few times before sailing away.

As many of you know, there are two types of Black-capped Petrels that we encounter offshore here, white-faced and dark-faced birds.  There are also many that fall into an intermediate category.  Molt timing and genetic analysis in these two types of Black-cappeds indicates two different nesting populations.  Nesting birds on Hispanola that have been documented and/or tagged have all been dark-faced or intermediate birds.  This spring an ongoing project by ABC (American Bird Conservancy) to capture these petrels at sea came to Hatteras with a new method for capture and tags for up to ten birds.  Their focus was to capture and tag the white-faced birds so they would perhaps lead us to an unknown nesting location.  We were lucky enough to partner with ABC, South Carolina Cooperative Fish and Wildlife Research Unit, and Birds Caribbean - Black-capped Petrel Working Group for this expedition.  Chris Gaskin of the Northern New Zealand Seabird Trust brought his one of a kind net gun that was key to the success of this expedition!  The ABC press release is here: May 2019 marked the first time that Black-capped Petrels have ever been captured at sea!  A website tracked the individuals with GPS tags over the summer and now, two birds are still transmitting, one white-faced and the other dark-faced.  The white-faced bird headed to Hispanola at the end of September and has been there since over land and at sea, while the dark-faced bird was still at sea to the east of Cape Hatteras.  A link to the map is here:  It looks like the white-faced bird could possibly be on a pre-laying exodus to the north of Hispanola right now after spending some time near one of the known breeding locations.

White-faced Black-capped Petrels have never been documented nesting on Hispanola (until possibly now), but that doesn't mean they are not there.  So perhaps there are just two populations with staggered nesting times on Hispanola, perhaps both types of Black-cappeds nest in the same fashion elsewhere in the Caribbean.  Dominica has sufficient petrel activity for us to believe that they are nesting there, perhaps only white-faced birds are there, perhaps both - no one yet knows because a nest has not been found there to date.  So our observations on this past trip are interesting, especially when we can look at the types we found out there this month.  The majority of the birds seen and photographed were dark-faced (Peter Flood)
or intermediate types, though there were at least three white-faced birds photographed.  For what it's worth we see more white-faced birds in the spring here, this could be because by fall most have moved closer to the nesting grounds in the Caribbean.  There is still a lot to discover about our signature species, the Black-capped Petrel, locally known as Diablotin on Hispanola.  And while we are very lucky to see them on just about every trip offshore from Hatteras, their true population size is unknown, likely in the low thousands.  We also know little about threats they face at sea because their movements in the deep waters of the Atlantic are mostly unknown but for at sea observations, and a small number of GPS tracks.  Pulling all of this together, the luxury of spending a day in the company of fifty of these enigmatic gadflies becomes quite clear!

Thanks to everyone who joined us offshore for this October trip and to Kyle Kittelberger for helping us as a leader!  Thank you also to Peter Flood for contributing photos for this post.

Species List
Black-capped Petrel - 49 to 57
Cory's Shearwater - 52
Scopoli's Shearwater - 1
Cory's type - 20
Great Shearwater - 27
Audubon's Shearwater - 12
Wilson's Storm-Petrel - 4 to 5
Pomarine Jaeger - 1
Pom / Parasitic - 1

Common Loon - 1
Herring Gull - 6
Laughing Gull - 18
Sandwich Tern - 7 to 8
Dunlin - 1
sandpiper sp - 1
Mourning Dove - 1
Cedar Waxwing - 1
Common Grackle - 1
Brown-headed Cowbird - 1

Bottlenose Dolphin - 5
Ocean Sunfish (Mola mola) - 1
Portuguese Man of War - 4

A dark-faced bird (Kate Sutherland)
And one that is more intermediate (Peter Flood)
Great Shearwaters were with us all day in the slick giving some nice comparisons with Black-capped Petrel.  Superficially they seem to have similar markings, but when seen in life they look quite different from one another! (Kate Sutherland)
Our very cooperative Pomarine Jaeger in flight (Peter Flood)
flying with one of the Great Shearwaters (Peter Flood)
& on the water with a Great Shearwater (Kate Sutherland)
One of the offshore Bottlenose Dolphins (Kate Sutherland)
And finally, a chub mackerel that was on the surface near the boat! (Kate Sutherland)