Pelagic birding off southern Oaxaca and the Townsend’s Shearwater

20 September 2013

Nowhere else on the Pacific Coast of North America is the continental shelf as close to shore as it is off of southern Oaxaca. From Puerto Angel the shelf edge begins to fall off into the Middle American Trench as close as 3-4 miles from shore, and approximately 20 miles off shore you encounter over 12,000 feet of water. The sea is quite rich here and the list of birds possible here is tantalizing – along with birds common to Mexico’s West Coast it is a great spot for Galapagos Shearwater and probably the best place in the world to find the critically endangered Townsend’s Shearwater shy of the very difficult to access Revillagigedo Islands where they breed. Additionally there is a chance for Christmas Island Shearwater, and you only need to get out 15-30 miles offshore to have a chance (albeit slim) for a huge range of tropical petrels (Hawaiian, Tahiti, Parkinson’s, Kermadec, Juan Fernandez and probably others lurk out there) as well as Masked and Nazca Booby. With this in mind, we had been eagerly anticipating the possibility of a pelagic here for the entirety of our trip.

Black Storm-Petrels were one of the most common species we saw.

There are two distinct options for a pelagic here. The first is to stay in closer to shore (perhaps 2-8 miles offshore) to look for the Townsend’s Shearwater among the Galapagos, Black-vented, Wedge-tailed and Pink-footed Shearwaters, Black, Least and Chapman’s (Leach’s) Storm-Petrels, Brown and Blue-footed Booby, and various terns. Alternatively, you can head for deep water and look for petrels and other rarities.

This Black Tern was one of hundreds we saw, some resting on flotsam, some foraging in large flocks.

We arranged for a roughly five hour trip and headed out at 7:30 AM, in fairly smooth water with a moderate long period swell. We hurried out to about 5 km offshore where we found some Black-vented and Galapagos Shearwaters as well as Black, Least and Chapman’s (Leach’s) Storm-Petrels fairly quickly. We chummed a little which brought some Storm-Petrels in closer, but we didn’t encounter any big concentrations of birds so we kept heading out deeper. We continued straight out and made it out about 18 km offshore, at which point we hadn’t seen a Shearwater in a long while, and Storm-Petrels were thinning out quite a bit so we decided to move back in closer to shore to look for Townsend’s Shearwater rather than continue out, hoping for a Petrel or Nazca Booby. We turned north west, heading back towards shore on a diagonal, and when we were back about 8-10 km from shore started to see Black-vented and Galapagos Shearwaters again, along with larger numbers of Storm-Petrels. We got to about 5-6 km offshore when we made a turn to head back east, paralleling the coast. Shortly thereafter we came upon some activity so we killed the engine and chummed a bit, watching hundreds of migrant Black Terns foraging in tight groups around us with a good number of Storm-Petrels flitting about as well. A few Black-vented Shearwaters seemed undisturbed by the boat and sat on the water no more than 4 meters away. Soon another shearwater, roughly the size and coloration of a Black-vented, came speeding along the side of the boat about 60-80 meters out. I saw it and took a quick look. Initially as it was further away, it looked like a Black-vented, but as it got closer I picked up the camera to get some photos. As I was fighting to try to focus on the bird on a rocking boat, it looked increasingly interesting. About this time, Kathi shouted out that she saw the white saddle marks which are the best field mark for identifying the Townsend’s Shearwater. I saw this as well while getting some frustratingly blurry photos. The facial pattern and dark swath on the neck were also visible, but unfortunately the Townsend’s Shearwater kept moving in a straight line and was soon out of view. We both saw it very well but sadly my photos are all poorly focused.

The white saddle bag marks coming up onto the sides just behind the wings, along with the dark swath on the neck, are the two best field marks for a Townsend’s Shearwater in among Black-vented Shearwaters.

Shortly thereafter we also found a Brown Noddy feeding with the Black Terns, which was a nice surprise. A few Jaegers were about as well, and looked like they were probably Parasitic Jaegers, but were too far off to ID. A few Sabine’s Gulls were in the area, which is one of our favorite pelagic birds, they are very striking. One last treat was a Sabine’s Gull and a Jaeger sitting on the water together that allowed us to approach close enough to tell that the Jaeger was a Long-tailed Jaeger, definitely another good find and a great cap to our little pelagic trip!

This Long-tailed Jaeger let us approach quite close. Despite having molted it’s inner retrices, the cap and bill, and more importantly the two toned upper wing, and limited white flash in the wing, point to Long-tailed Jaeger over Parasitic.

We were pleasantly surprised to find this Brown Noddy foraging with one of the flocks of Black Terns.

Unfortunately, Townsend’s Shearwater is critically endangered and the tiny population (believed to be fewer than 1000 birds and fewer than 100 breeding pairs) is believed to be declining rapidly. It has been extirpated from two of its three breeding islands and is threatened by feral cats, overgrazing and trampling of burrows by sheep, and light pollution on Isla Socorro, its remaining breeding island. Most shearwaters, petrels and storm-petrels come to islands at night to nest in rocky crevices or underground burrows. All over the world, this leaves them very vulnerable to predation by introduced cats, rats and mice, as well as grazing animals that trample on top of their burrows causing them to collapse. Beyond the simple issues of habitat loss as humans populate islands and build roads and towns, the light pollution we cause disorients them in the night and they end up in towns, where buildings, cats, dogs and cars are a huge problem for them. While the Townsend’s Shearwater does face large problems on Isla Socorro, the fact that Socorro is not a highly populated island is one positive for a bird with an otherwise bleak future. With relatively modest resources introduced predators could be removed from Isla Socorro and Townsend’s Shearwater (along with several other troubled endemic species on the island) would have a much better outlook on life. This seems, to me, a very solvable issue and one that I would like to help with. We certainly felt tremendously lucky to have seen this rare bird.