Los Cóbanos revisited

Wandering Tattler

Roselvy and I went birding today in Los Cóbanos, a coastal spot in southwestern El Salvador. By bus it's quite a trek from San Salvador, and we didn't get there until lunch time. Sundays this place is packed with daytrippers enjoying fried fish, cold beer and loud music. Not caring too much for the loud music, we walked a couple of hundred meters to another, quieter beach, where we sat down at a more modestly priced eatery.

Scanning the ocean while munching on some fried fish, I found a bird that I don't think I have ever seen in El Salvador before: Least Tern. It was maybe 250 m away, i.e. not close, but definitely within the realm of confident identification for me. Too far for a photo, though.

This could be a noteworthy sighting. Howell (1995) shows the bird wintering in southern (Pacific) Mexico, but places question marks on the Guatemalan coast and in the Salvadoran-Honduran-Nicaraguan Gulf of Fonseca. The BNA account (Thompson et al. 1997) merely copies these question marks. It also states that the species was "not found during focused search of Pacific coast of Costa Rica during Jan" (Thompson et al. 1997) - but eBird has a few January records for Pacific Costa Rica, and a few more for December. Yay for eBird!

But of course it has no December or January records yet for El Salvador, because who after all birds El Salvador…? (And yes, I did enter today's sightings into eBird. Soon there will be a green dot in El Salvador for this species…) 

Semipalmated Plover and Least Sandpiper

Other birds we saw were more expected, and included Wandering Tattler, Least Sandpiper, Semipalmated Plover, Spotted Sandpiper, Tricolored Heron, Snowy Egret, Green Heron, Brown Pelican, White-collared Swift, Cave Swallow, and Barn Swallow.

Tricolored Heron

References:
Howell, S. N. G. and S. Webb. 1995. A guide to the birds of Mexico and northern Central America. Oxford Univ. Press, Oxford, UK.
Thompson, Bruce C., Jerome A. Jackson, Joannna Burger, Laura A. Hill, Eileen M. Kirsch and Jonathan L. Atwood. 1997. Least Tern (Sterna antillarum), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/290

An influx of Chuck-will's-widows?

Chuck-will's-widow, female in pine-oak, Montecristo, El Salvador

Several recent posts have been about unusually late migration of various bird species. For example, I had a late Sulphur-bellied Flycatcher in November in Tortuguero, Costa Rica. I wrote about an early December wave of Scarlet Tanagers also in Costa Rica, and the previous post was about a late push of juvenile Broad-winged Hawks into El Salvador last weekend.

My friend Oliver Komar pointed out in a comment on that last post another exceptional sighting last weekend, i.e. that of a Chuck-will's-widow, a bird noted in small numbers in fall migration in El Salvador, but rarely encountered there after the second half of November. He speculated that the juvenile broadwings we saw migrating had been knocked down by a couple of severe cold fronts that passed through the southeastern US recently, bringing frosts to areas all along the northern Gulf Coast, and that perhaps the same thing was going on with Chuck-will's-widow.

Chuck-will's-widow, male in tropical dry forest, Deininger, El Salvador

Monday December 13, Roselvy, Carlos and I saw a Chuck-will's-widow on the road to the cloud forest in national park Montecristo, El Salvador. On Saturday December 18, the Partners in Flight - El Salvador field excursion participants found one roosting in national park Walter Deininger, El Salvador. And then yesterday, we stumbled upon another one, again in Montecristo, but at a lower elevation, in the pine-oak forest. According to Oliver Komar, Chuck-will's-widow is rarely recorded in El Salvador in December, and three sightings within a couple of weeks could be indicative of an influx of this species into the area.

Caprimulgids are usually more readily identified by call, and visual identification of the members of this family is not easy. It may be worth briefly considering the field identification of our birds.

The first clue should be its apparent size: Chuck-will's-widow is larger than any other nightjar, resident or winter visitor, in the region. The BNA account states rather confidently that "size, tail pattern, lack of white (or buff) in wings, and overall rich brown coloration serve to eliminate nearly all other Caprimulgidae" (Straight & Cooper, 2000), with the exception of Rufous Nightjar, a species found in Costa Rica and further south.

Given its highly cryptic plumage, its retiring daytime habits, and its similarity to other nightjars, this species can easily go undetected when present. In fact, the extent of its winter range is still rather poorly understood, and largely based on specimens in collections rather than reports of birds in the wild, of what is after all not a rare species. eBird, for example, still has precious few wintering grounds records. According to BNA, chucks winter from east-central Mexico south throughout Central America and into northern South America. It is also found as a winter visitor in the West Indies (Straight & Cooper, 2000).

So... did we accidentally stumble upon three individuals of a species that regularly winters in El Salvador but often goes undetected? Or is this a normally rare winter bird in El Salvador that somehow this early winter is much more common here than usual?

References:
eBird. 2010. eBird: An online database of bird distribution and abundance [web application]. Version 2. eBird, Ithaca, New York. Available: http://www.ebird.org. (Accessed: December 24, 2010).
Straight, Carrie A. and Robert J. Cooper. 2000. Chuck-will's-widow (Caprimulgus carolinensis), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/499

Exceptionally late Broad-winged Hawk migration

juvenile Broad-winged Hawk

I'm back in El Salvador. Yesterday, I went on a field excursion organized by the Salvadoran branch of Partners in Flight (PIF), the principal club of bird observers in El Salvador. We went to Walter Thilo Deininger National Park near the coastal town of La Libertad, where we saw a fair number of interesting birds - really more than any of us had expected.

By far the most noteworthy sighting, however, was of a group of 17 Broad-winged Hawks - later followed by smaller groups for a total of at least 40 individuals - apparently migrating over the site!

All birds were juveniles.

juvenile Broad-winged Hawks kettling over the park

As far as I'm aware, this late migration of juvenile Broad-winged Hawks has not been previously described - for Central America, or indeed any other site. The species winters in northern South America and throughout Central America; a small number winters in southern Florida and the lower Mississippi Delta and coastal Texas. The majority of birds that winter in the US are juveniles (Goodrich et al. 1996).

juvenile Broad-winged Hawks in a glide over the park

Highly gregarious in migration, the species can be seen in large congregations in the northeastern US during the second half of September, Texas late September, Mexico early October. Fall migrants are noted in Costa Rica and Panama from late September to mid-November, but most pass through in October (Goodrich et al. 1996). 

juvenile Broad-winged Hawk

Separate migration of age classes is well-known during spring migration, when the majority of adult Broad-winged Hawks precede the majority of juveniles by about two to three weeks. In fall, all ages usually migrate together (pers obs).

Flying with the broadwings were single individuals or small groups of two or three Turkey Vultures. This surprised me less, as a small percentage of Turkey Vultures is known to linger and migrate opportunistically. Mexican hawk counters in Veracruz told me it is often possible to see Turkey Vulture movement well into December.

References:
Goodrich, L. J., S. C. Crocoll and S. E. Senner. 1996. Broad-winged Hawk (Buteo platypterus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/218

Last day in Tortuguero

Well, the monkeys were right and I was wrong, of course.

Mantled Howler Monkeys are excellent short-term weather forecasters, no doubt because their place high up in the canopy provides them with fabulous views of the sky. So when I opened the nets today around noon, when the rain seemed to let up a little bit, it was accompanied by hoots of derision from across the river.

Indeed an hour or so later it was raining again, and it never stopped. Bird banding can take place in light rain, so I ran the nets for two hours, in hopes of a surprise maybe on my last day of banding in Tortuguero, Costa Rica. But all I caught was a Gray Catbird, a female White-collared Manakin (recapture), and one of the pair of Northern Barred Woodcreepers that have a territory around the net lanes. The poor woodcreeper I released without processing this time, for it has already participated generously in this study.

The above photo is from a few days ago, and shows a wing of a first-year female Scarlet Tanager. I'm afraid this is the kind of bird photo only hardcore banding nerds will appreciate, for it shows a molt limit in the greater coverts, by which we can age this bird as a HY (hatch year) individual. Yeah, I know...

Late Scarlet Tanager migration?

Scarlet Tanager

It's December, and as expected, bird migration is pretty much over. This is my last week of bird banding in Tortuguero, and I'm catching mostly residents now, plus the occasional winter visitor.

And... one other species that's neither a year-round resident nor a winter visitor here: Scarlet Tanager.

Apparently, this species is still migrating!

In fact, four out of five of my Scarlet Tanager captures here - and I've been banding from October 21 until today - have been in December. All five individuals were hatch year birds. There was a bird (male or female) on 12 November, followed by a male on December 3, then a female on December 6, and both a male and a female on December 7.

The BNA account for this species says that "most birds do not depart breeding grounds until mid- to late Sep; at Cape May, NJ, peak fall migration 10-20 Sep; Georgia late Sep - early Oct. Departure from Gulf coastal states by mid-Oct. Arrival dates at wintering grounds poorly documented, but the few available records suggest birds reach Colombia by mid-Oct, Ecuador by 1 Nov, and Bolivia by mid-Oct to mid-Nov" (Mowbray 1999).

Scarlet Tanager is a trans-Gulf migrant, and part of the route in fall is through Central America (including Costa Rica). See Fig 1 below.



Figure 1: Scarlet Tanager breeding range, migration routes and winter range.  
By Lincoln, Frederick C., Steven R. Peterson, and John L. Zimmerman. [Public domain], via Wikimedia Commons. Image courtesy of the U.S. Geological Survey.

Wondering if this little early December wave, apparently consisting entirely of first-year individuals, is something unusual or in fact annual, I consulted eBird. Here's an animated gif of all Scarlet Tanager 'fall' records in their database, ordered by month, starting with July, and running until December. See Fig 2 below:



Figure 2: Scarlet Tanager records in eBird by month, from July until December.  
Image provided by eBird (www.ebird.org) and created 8 December 2010.

Observer effort of course varies widely along the Scarlet Tanager's range, which explains why the wintering grounds don't all light up green as the breeding grounds are vacated. Still, we can see Costa Rican records light up in October and November, and then none for December!

How curious then that I caught zero Scarlet Tanagers during the second half of October, only one in November, and then four in the first week of December!

References:
eBird. 2010. eBird: An online database of bird distribution and abundance [web application]. Version 2. eBird, Ithaca, New York. Available: http://www.ebird.org. (Accessed: December 8, 2010).
Mowbray, Thomas B. 1999. Scarlet Tanager (Piranga olivacea), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/479

A family affair?

Sandwich Tern with Royal Terns

Here in Tortuguero, on the Caribbean coast of Costa Rica, Laughing Gulls have only been around in numbers since a week or two, but Royal Terns have been common at least since I got here, mid-October.

Yesterday afternoon, I walked out to the mouth of the Tortuguero River, where a number of them can usually be found.

About a third of the individuals in this group were banded. A little bit of online research showed me there's a considerable banding effort on the United States Eastern Seaboard each year, involving thousands of Royal Terns being banded in Maryland, Virginia and North Carolina. Go here for an account of a Honduran intern's experience banding Royal Terns with the Maryland Coastal Bays Program.

Four of the five banded individuals I saw can be seen in this photo. Even within the group, they seemed to associate more closely with each other, something I'd noticed with banded individuals in New Jersey and El Salvador also. According to the BNA account, Royal Terns are "highly social and gregarious throughout the year, assembling into compact flocks up to several thousand, often in family groups, but occasionally solitary outside the breeding season (Buckley & Buckley 2002, emphasis added).


References:
Buckley, P. A. and Francine G. Buckley. 2002. Royal Tern (Sterna maxima), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/700

Mangrove Cuckoo

Mangrove Cuckoo

According to one Costa Rican field guide, Mangrove Cuckoo is an "uncommon to locally fairly common nonbreeding visitor (December—June) in lowlands and foothills of northern Pacific slope, becoming rare south along coast and in Golfo Dulce district; locally to 3600 ft (1100 m) as in western Valle Central; on Caribbean slope regular only in extreme northwest, rarely east to Río Frío region; may breed in very small numbers in lowland Guanacaste" (Stiles & Skutch 1989).

The more recent Garrigues & Dean (2007) summarizes this information, noting the bird is a "fairly uncommon Central American migrant from December to June in northwestern Pacific lowlands; uncommon to rare in southern Pacific lowlands and in western Central Valley."

Not a bird then one would expect on the Caribbean coast.

However, the checklist for Tortuguero, found in Ralph et al. (2008), does list Mangrove Cuckoo as a rare resident.

Mangrove Cuckoo

Here it is, poking its head out of the vegetation. I found this bird on an afternoon walk today near the Mawamba Lodge, a couple of hundred meters from where I'm staying here in Tortuguero (CCC).

Note the all dark upper mandible, the absence of rufous in the wing, the more pronounced dark mask, and the buffy wash on the underparts - all features that distinguish this species from Yellow-billed Cuckoo. There's a difference in the tail pattern also, but these photos don't capture that aspect very well.

Cited literature:
Garrigues, R. and R. Dean. 2007. The Birds of Costa Rica: a Field Guide. Cornell Univ. Press, Ithaca, NY.
Ralph, C.J., M. Widdowson, B. Widdowson, B. O'Donnell & R.I. Frey. 2008. Tortuguero Bird Monitoring Station Protocol, unpublished draft version January 2008.
Stiles, F. G. and A. F. Skutch. 1989. A guide to the birds of Costa Rica. Cornell Univ. Press, Ithaca, NY.

Stormy weather

A couple of days ago, it started raining here in Tortuguero, on the Caribbean coast of Costa Rica, and it hasn't stopped since. The rain has been heavy at times, which even caused a power outage for most of the morning today.

As the rain was letting up a bit towards midday, I thought I'd venture out on the beach to see what's doing.

Immediately I realized that the birding there was as fabulous as it was difficult. Strong winds, darkness from heavy overcast skies combined with the rain made for very poor visibility. But there was a good number of birds out there, especially Laughing Gull was abundant. There was a constant stream of laughers heading southeast parallel to the beach, and I think I saw nearly a thousand individuals in about an hour's time.

Black Noddy

Other birds seen were two jaeger spp., a Common Tern, a couple of sulids, and this bird, a Black Noddy. Unlike the others, this is a true pelagic and not normally seen from the beach here.

The sulids were likely Brown Boobies, a species that I see regularly off the beach here, even in calm weather. Although I wouldn't rule out Red-footed Booby. Last Sunday, someone brought in a sickly booby, which died later that day. Despite its yellow legs and feet, certain measurements (specifically tarsus and tail) and plumage characters (uniform dark plumage, light tip to dark tail) pointed in the direction of the locally much rarer, because much more pelagic, Red-footed Booby.

Brown Booby

This bird, however, I believe is a juvenile Brown Booby.