Hi Everyone,

I have some thoughts that I wanted to share about the status of recent Brown Booby reports from Assateague Island. 

Ron Gutberlet and I reported an interesting sulid on 19 July, and Frode Jacobsen photographed an immature Brown Booby on 22 July. Frode's photos are likely to provide the basis for Maryland's first record of Brown Booby. This excellent find by Frode arrives, by the way, at the exact time and place predicted in "Maryland's Next 10 Bird Species." Since then, there have been many reports of Brown Booby from the ORV (=OSV) zone, one of which I shared with about ten other observers on Sunday, 26 July. 

We noted distinct differences in flight style from expected Northern Gannet flight. We felt that structural differences were pronounced, especially after seeing a confirmed Northern Gannet an hour later. Our candidate even dove more than once at a 45-degree angle. The plumage details we could discern all supported Brown Booby over Northern Gannet. What's the problem then? The problem is that morning viewing conditions looking east from Assateague are horrible, we're viewing very distant birds, and confirmation bias is powerful even when you are actively resisting it. I had my settings at maximum b.s. resistance, but I LIKED this bird. We all really liked it. 

The description, which I wrote with validity wording and an effort at objectivity, seemed convincing. My photos are very distant, but the ones I shared appear generally supportive of Brown Booby. I have a shot of it diving at a perfect 45-degree angle. 

HOWEVER...

Over the last couple days, I have spent hours reviewing just about every Northern Gannet and Brown Booby photo on the Internet. I just knew I'd find the evidence to lock down the ID. I found some additional support, and I also noted some differences that seem consistent in all photos of the two species. Last night, I decided to make my second pass through my nearly 800 photos of our candidate. I spent about 3 hours analyzing every single 12+ megabyte RAW file to look at structure and plumage. Unfortunately, instead of confirming the ID, I am confident that I proved the Sunday bird was a Northern Gannet. 

(* Since much of the ID discussion has taken place off-line, the Saturday photos have been considered strongly suggestive of Northern Gannet as well.)

THE DETAILS

Basically, we need to eliminate this guy, which I photographed on a Poor Man's Pelagic in Maryland at the end of May:

http://www.billhubick.com/images2/northern_gannet_end_of_first_cycle_20090530.jpg

This is a second-year (SY) gannet destined to spend a non-breeding summer on the Maryland coast. He's out there right now. This exact plumage, "Trashed Summer SY" we might call it, is not shown in most of the field guides. Note the superficial similarities to Brown Booby (think distant) and the heavy state of flight feather molt - you can see the replaced inner primaries. Nearly two months later now, I understand these uncommon but very regular summering birds generally look pretty beaten up. 

I downgrade "Sulid sp./Probable Brown Booby" to "Northern Gannet" based on the following:

** Extent of brown on the throat and breast: In reviewing hundreds of Brown Booby photos, I noted with interest how consistent in all ages was the extent of the distinct brown border at the lower breast. In every flight photo I can find, this border is nearly perfectly in line with the leading edge of the wing. Regardless of angle, it doesn't seem to ever start well ahead of the leading edge, or to taper forward toward the bill. In young gannets, the border starts further up on the neck and often angles forward (see linked SY gannet photo again). In several of my photos, it's there. It's blurry and its 'CSI Assateague,' but it's there. The border does not go to the lower breast. It's on the throat, and it's well forward of the leading edge of the wings.

Molt: Brown Booby molt is entirely different from that of Northern Gannets, and Brown Boobies are far less likely be in heavy molt right now. Frode's photos show that his bird was definitely not in significant molt. We didn't see molting feathers in the field, but reviewing hundreds of photos, it's there. Our bird seems like it was pretty trashed in its flight feathers when it caught a bit of human-friendly light. These birds are just really far and really backlit.

But what about...

ALL BROWN BACK / NO WHITE UPPERTAIL COVERTS / NO WHITE IN UPPERPARTS: As I feared, I am now convinced that the morning light looking east from Assateague does not allow reliable calls on these field marks. Our bird looked just fine, but the backlighting is awful. It wasn't until 11:00 a.m. on Sunday that we could confidently note plumage details on even many of the closest Sterna terns. John Hubbell has a good anecdote about returning to Assateague in the afternoon and being thrown off by how light the passing Whimbrels were - they were so much darker in the morning.

STRUCTURAL DIFFERENCES: I believe it's just too far to be confident, especially with an irresistible (however slight) confirmation bias. I've seen several references, including in Sibley, about how surprisingly difficult this can be to judge. Also, see the following.

FLIGHT STYLE: Flag this as speculation. Could it be that immatures such as SY birds need to flap more because of heavy wing molt and missing/incoming feathers? Could that even result in a subtle difference in overall impression? Most of us consider ourselves experts on gannets, but how many have we intensely studied in summer? For me, at least, it's quite few. I do not argue that our first sulid left a distinct impression from the later (and older) gannet... but both were gannets.

45 DEGREE ANGLE DIVE: I was REALLY excited about this. I knew for a while that low-angle dives were suggestive of boobies, but then I read some quotes that seemed to indicate that they were diagnostic. When I saw our Sunday bird dive this way, I practically jumped up and down. I was even more thrilled to see that I had a photo of it. Unfortunately, this dive is from approximately 50 feet above the water, which is weird. In checking with one expert, it was suggested that a truly diagnostic observation would be a low-angle dive from, say, 5 to 20 feet over the surface after shearwater-like flight. Although this observation is of interest, it is not enough. 

WHERE ARE THE PHOTOS?

I don't have any photos posted on my web site yet, and it will take me through the weekend to put up a series to make my case (on the wrong side that I wanted to be on). This was serious Photoshop forensics, so it will require a longer series of worse photos than I would ever normally post. I have visitors in town through Saturday, so Monday is about as early as I can send them out.

SO...

There has not been any conclusive evidence (i.e., unequivocal photo documentation) - that I know of - since Frode's flyby Brown Booby. I welcome discussion and PLEASE talk me back into our bird after I post the series of terrible photos. Please understand that I am not attacking specific reports, and that there very well may be a lingering Brown Booby. If not, another one could certainly show up tomorrow and sit on the Great Cormorant post beside the Atlantic Motel through the end of August. That said, I hope that everyone will read and consider all of this. With increasing rarity, there is a corresponding need for documentation. Hopefully we'll really lock down a Brown Booby - and a damn spoonbill - in the near future. Will I still be out there on the ORV zone as soon as possible? OF COURSE!

Thanks, and good birding!

Bill

Bill Hubick
Pasadena, Maryland

http://www.billhubick.com