Saturday, October 25, 2014

Non-Seabird Species Observed From a Cruise Ship

Blackpoll Warbler image by R. Rodriquez Mojica

(All images were downladed from the CD that accompanies Mark Oberle's book "Puerto Rico's Birds in Photographs", Third Edition, 2010)

Considerable debate occurs among birders over whether or not a species occurrence in an area was human-assisted.  The most angst seems to revolve around whether the bird was released from a cage (welcome to Miami!) or if it arrived at its location because of being ship-assisted.  The theory behind the latter is - is it legitimate to count a speices as a "wild" bird after it traveled all or a portion of of their journey on a ship.  

The entire concept of human-assistance in a birds presence and your ability to observe it is actually a moot point. Viewed logically, the only bird whose observation wasn't human assisted in some way is the one you see in natural habitats of its range that are viewed with your bare eye.  A flock of Snow Geese foraging in a North Dakota wheat field are on that field because human’s plowed up the prairie and converted it to wheat that the Snow Goose eats.  Were it not for that human assistance the geese wouldn’t be where they are.  Seeing a Black-capped Chickadee in your backyard while it forages at a bird feeder is also a human-assisted bird.  It likely wouldn’t be in your backyard had it not been for the bird feeder.  Water birds in my development that forage on fishes and amphibians in the large wetland here are all human-assisted because the wetland wouldn’t be there unless human’s constructed the wetland.  Lastly, a migrating Hooded Warbler seen on Lido Key when it was fifty feet up in a tree and you observed it through binoculars is also human-assisted because humans built the binoculars through which you are viewing the bird.  

Were it not for the human-made binoculars through which you are looking (not to mention the human planted Australian pine that the bird was in) you’d likely never see the bird or be able to identify it.  In short, unless you see the bird hatch from its egg, and then track it for the remainder of its life, you really don’t know it its presence in front of you was human-assisted or not.

Finding non-seabirds on the ocean is logical given that so many species migrate over the open ocean to reach their winter habitats.  Fall migration of the Blackpoll Warbler is an interesting example.  This species nests in boreal forest across central and northern Canada and into Alaska as far as the Seward Peninsula north of Nome.  In fall the birds fly east and congregate on the coast of Atlantic Canada before pitching out over the ocean toward Venezuela.  It is estimated that most Blackpoll Warblers make a 4-5 day long non-stop flight after leaving solid ground.   Recently a group from the US Fish and Wildlife Service wildlife biologists affixed a satellite transmitter to the back of a Bar-tailed Godwit and tracked its south bound migration from Alaska to New Zealand.  To the amazement of everyone involved the Godwit made the 7,000 mile migration nonstop.

The first non-seabird I ever saw on the ocean was from a seabird watching trip from Cape Hatteras, North Carolina in September 1984.  We were aboard a boat called the Crystal Dawn on a trip organized by Bob Ake and Paul DuMont, when we found a Clapper Rail swimming around in the Gulf Stream current some 40 miles from land.  Since that time I’ve seen several flocks of Blue-winged Teal headed south over open ocean along with flocks of sandpipers (of various species).  In October 2013, on a cruise from Miami to Grand Turk Island in the Turks and Caicos Islands I observed an exhausted adult Peregrine Falcon come aboard the ship while we were 100 miles east of Eleuthera Island in the Bahamas.  Later a presumed juvenile Osprey was observed circling the ship and briefly came onboard on several occasions.  Both the Osprey and the Peregrine Falcon stayed briefly enough to catch their breath before continuing their journey south. 

Both of those birds were human-assisted or ship-assisted but had I not been onboard the ship, nobody would ever know if they were ship-assisted.  They were ship-assisted at one point in their migration but by the time they came ashore there would likely be no ship around so how can you tell the difference?

The American Birding Association held a forum in one of its journal issues where “experts” debated the validity of birds, the probability of them being human assisted, and the resultant countability of that bird for your various lists. Their findings and recommendations were very restrictive.  The British Ornithological Union takes a more liberal approach and almost without exception accepts a bird’s identification regardless if it’s ship-assisted or otherwise human-assisted when it was seen. 

On a recent transatlantic cruise I conducted up to 6 one-hour long transects each day of birds observed on the ocean as we crossed the Atlantic from Copenhagen, Denmark via Ponta Delgada, Azores and St. Thomas in the U.S. Virgin Islands to Miami. Between Copenhagen and St. Thomas I saw several interesting seabirds but no non-seabird species.  That changed as we steamed west and north along the coast of Hispaniola and Cuba on October 18 and October 19, as the ship approached south Florida and the harbor in Miami.

Over those two days at sea I observed 8 different non-seabird species while on the ocean.  Another person onboard saw an additional species (Great Egret) that I missed.  Our luck in finding non-seabirds was enhanced because mid-October is at or slightly past the peak of southbound migration for many bird species.  Below is an account of the eight non-seabird species I observed on that trip along with some commentary and speculation about each occurrence.

Great Blue Heron (Ardea herodias) – At about 8:00 a.m. local time on October 18, and at a point about 15 miles north of the Samana Peninsula of the Dominican Republic, I observed three Great Blue Herons briefly land on the helipad at the rear of the Norwegian Cruise Line’s “Norwegian Star.”  The birds remained standing on the pad until humans frightened them back into flight.

Digital Image by M. Morel

Snowy Egret (Egretta thula).  At about 9:20 a.m. local time on October 18 and at a point about 20 miles from the Samana Peninsula of the Dominican Republic a group of three obvious Snowy Egrets flew over the ship headed south.  They likely could see the coast of the Dominican Republic (I could so why couldn’t they?) and kept flying in its direction.

Digital Image by M. Morel

Zenaida Dove (Zenaida aurita) -  Shortly after sunrise on October 19 and at a point about 20 miles off the northeast coast of Cuba, a Zenaida Dove passed in front of me as I was attempting to count seabirds.  To my knowledge that bird did not land on the ship however I have no way of knowing if that is entirely true.  At the point where it was observed we were about equidistance between the Cuban coast and Great Inagua Island in the Bahamas.  The bird’s flight direction was northeastward so I assume it was headed toward Great Inagua or one of the other islands nearby.

Digital image by R. Rodriquez Mojica

Bicknell’s Thrush (Catharus bicknellii) – At about 4:00 p.m. local time on October 18, and at a point about 20 miles due north of Cap Haitien, Haiti, a Catharus thrush of some species flew along the side of our ship before eventually landing on the rail of the balcony of our stateroom. Whether it saw me or not is unknown but the bird remained on our balcony rail for 5 or 6 minutes before departing.  Later in the day toward sunset I found the bird roosting on a wire suspended from the top of Deck 14 of the ship that passed over the pool and hot tub area. I do not know if it remained on board overnight.  Bicknell’s Thrush has one of the most restricted breeding and wintering ranges of any North American songbird. Almost without exception they winter in the mountains of the Dominican Republic and Haiti.  A bird in the cloud forest of the Dominican Republic not far from the border with Haiti in March 1985 (before the species was split from Gray-cheeked Thrush) was the first one I ever saw.  Subsequent trips to that mountain range in winter have revealed more Bicknell’s Thrushes but never in large numbers. 

Gray Catbird (Dumetella carolinensis) – At about 2:15 p.m. local time on October 18, and at a location about 30 miles north of Monte Cristi, Dominican Republic, a Gray Catbird made a brief appearance as it flew alongside (toward the west) our ship.  It landed briefly on the balcony of a nearby stateroom but I do not know how long it remained or its final destiny.

Digital image by Giff Beaton

Magnolia Warbler (Dendroica magnolia) – On October 18 at about 10:15 a.m. and at a location about 14 miles northeast of Puerto Plata, Dominican Republic, an exhausted juvenile Magnolia Warbler came aboard the ship along the Promenade on Deck 7.  There it rested briefly and then took flight.  After it left the ship it continued to circle the vessel as we steamed north and west away from that point and farther from land.

Digital image by Giff Beaton

Blackpoll Warbler (Dendroica striata) -  On October 18 at about 10:30, just minutes after the Magnolia Warbler arrived, a juvenile Blackpoll Warbler came aboard the ship on Deck 7.  It stayed briefly, foraged on some insects that were buzzing around the ship, then took up a position on the gunwale on the port side of the ship where it remained until at least 12:00 noon. I’m assuming it departed the ship but just as easily it could have flown to another deck and remained there for some time.

Black-throated Blue Warbler (Dendroica caerulescens) – At about 8:15 a.m. on October 18, at a point about 16 miles north of the Samana Peninsula of the Dominican Republic (and well within sight range of the island) an adult (I think) female Black-throated Blue Warbler came aboard the ship and stayed briefly.  After its departure I continued to see and hear the bird as it circled the ship as the ship continued to move slowly northwest and away from the coast of the Dominican Republic.
Digital image by Giff Beaton 

Are You Ever Really Certain of a Species’ Origin?

Songbirds are very well known to be nocturnal migrants but while migrating over open oceans they don’t have the luxury or opportunity to stop and catch their breath.  I’ve often wondered when passing through large forests of Sargassum or past sticks and other flotsam floating around in the ocean, if songbirds don’t occasionally stop on them for a rest.  Tropical seabirds like Sooty Tern and Brown Noddy are well known for resting on whatever they can find in the middle of the ocean so why not songbirds also?  That topic would make an excellent research question for some enterprising Master’s or PhD candidate to study.

One of the most ironic aspects of these observations is that with the exception of the Zenaida Dove, the other passerines and the Great Blue Heron each was within sight of land.  If you assume a 30 mile per hour migration speed, those birds were less than 30 minutes from reaching dry land where they would likely be spending the winter.  Each of these species, with the exception of the Snowy Egret and Zenaida Dove that never came onboard (to my knowledge), was close to the island where they would likely spend the winter.  However because of the need to rest they were transported further from the island and unless they found food onboard like the Blackpoll Warbler did, they each had to expend additional fat reserves to fuel the remainder of their migration. 

Six of the eight species observed were, in the strictest interpretation of the discussion, ship-assisted. However how could any observer in Cuba, the Dominican Republic or Haiti actually know that unless they were on the ship observing the birds as they passed over the ocean?  I can understand the angst generated by birders if someone opened a cage and out flew a Scarlet Macaw in downtown New Orleans.  However what about a Purple Martin migrating over the Gulf of Mexico that stops off on an oil production platform to catch its breath.  Technically it was human-assisted just like the herons and songbirds I observed come aboard a ship.  In the long run nobody ever knows and also in the long run unless the bird can be shown to have been released from a cage does it really matter?