Sunday, December 26, 2010

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

Friday, December 24, 2010

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

Sunday, December 19, 2010

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

Friday, December 10, 2010

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...

Wednesday, December 8, 2010

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.

Migration route scarlet tanager

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:

Photobucket

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

Monday, December 6, 2010

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

Saturday, December 4, 2010

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.

Wednesday, December 1, 2010

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.

Sunday, November 28, 2010

Laughing Falcon

Laughing Falcon
The Laughing Falcon is a fairly common raptor of lowlands and foothills found in Mexico, Central America, and most of South America. As the name suggests, it is a highly vocal species, and I hear its song, a characteristic sound of the Neotropics, almost every morning here in Tortuguero, on the Caribbean coast of Costa Rica.

Here it is, looking down for its favorite food, snakes.

The buffy tips of the back feathers indicate that this is an immature bird.

I think I also see a molt limit in the greater coverts, with two lighter and longer inner feathers contrasting with fresher outer greater coverts.

Saturday, November 27, 2010

Sooty Tern

Today, one the gardeners here at the Tortuguero Sea Turtle Conservancy handed me this bird, an adult Sooty Tern. He had found it in the water, unable to fly and just barely able to float, in the Tortuguero River near the river mouth.

I took the bird under my care and first made sure to dry it, as it was completely soaked. I checked for injuries but couldn't find any. The bird just seemed really exhausted, so I put it on a long-sleeve shirt in a carton box, and let it rest for a while. Three hours later, however, it was dead.

As I weighed it, and found that it only weighed 127 g, nearly half the weight of a healthy adult, I realized that it probably never had much of chance to begin with, poor thing.

Although globally one of the most abundant seabirds, in Costa Rica Sooty Tern is "a very rare visitor to Pacific coastal waters; no record yet for Caribbean coast" (Stiles & Skutch 1989). This is now outdated information (for example, there was a Tortuguero record last year, Pablo Elizondo pers. comm.) but the species certainly remains rare on the Caribbean coast. Heavy rains started last night and lasted until mid-morning; possibly this individual got disoriented in a nasty weather system.

Cited literature:
Stiles, F. G. and A. F. Skutch. 1989. A guide to the birds of Costa Rica. Cornell Univ. Press, Ithaca, NY.

Wednesday, November 24, 2010

Northern Barred Woodcreeper

Northern Barred Woodcreeper
With migration practically over, even down here in Tortuguero, Costa Rica, I want to take a look at another resident species, the Northern Barred Woodcreeper. Woodcreepers are a neotropical subfamily (Dendrocolaptinae) within the family of the ovenbirds (Furnariidae).

Their distinctively shaped tails provide strong support as they forage for small invertebrate prey on tree trunks. Note the width of the feather shafts on that tail!

Northern Barred Woodcreeper
This particular individual undoubtedly has a territory right where the 'CCC station' net lanes are, for I've caught it (#1245) and its mate (#1250) several times now. They have a distinctive, somewhat squeaky upslurred call that I hear frequently.

Northern Barred Woodcreeper
Most woodcreepers have brownish plumage, often with streaks. Within its range, on the Atlantic slope from southern Mexico through Central America to Colombia, Venezuela and Ecuador, it is the only completely barred woodcreeper, and thus readily identified.

Saturday, November 20, 2010

Green Turtle hatchlings


A few more shots and a little video of Tortuguero's most famous residents, the Green Turtles, Chelonia mydas. The breeding season is largely over for them, although I still find tracks of females on the beach every now and then. The female emerges from the sea and climbs on to the beach at night, shuffles for 25 m to a place beyond the high tide line, digs a hole and deposits her eggs in it. She then covers up the hole with sand, and returns to the sea.


Sixty days or so later, these guys emerge.


They are usually full of energy and go straight for the sea.


As small as they are, they are vulnerable to predators while making the 25 m journey to sea.


Almost there!

I've seen Green Turtle hatchlings on the beach a number of times now, but, as one of the turtle researchers here said the other day, it never gets old.

Here's a short video of a Green Turtle hatchling making the trek across the beach to the sea:


video

Thursday, November 18, 2010

Caño Palma

White-whiskered Puffbird
I returned yesterday to the "CCC" Biological Station in Tortuguero from a few days bird banding at another Biological Station, only a 20 minute boat ride from here, called Caño Palma.

Here are some fairly gratuitous photos of birds encountered there. I loved the banding at this site, where the emphasis is more on resident birds, less on migrants. That said, the most exciting capture probably was of a migrant: a recaptured Northern Waterthrush. This bird was first captured in Tortuguero in March of 2006, when its fat score was 'zero', and then again a month later, when it had fattened up for migration to a 'six'. And now we caught it again. Assistant bander Eveling Tavera caught and processed it, I actually never saw the bird. Thus, I have no photos of it.

But I've got shots of some pretty neat residents. The bird at the top is a male White-whiskered Puffbird, a bird found from southeastern Mexico to Ecuador.

Red-capped Manakin
This strikingly handsome bird is a male Red-capped Manakin, rarely seen at the CCC site but fairly easily observed at the Caño Palma site.

White-collared Manakin

The  male White-collared Manakin is also good-looking. The green females are common around the CCC site, in fact it's one of the most commonly caught species. But I have yet to catch an adult male. The adult males tend to hang out near their leks, where they perform a dance that involves a wing snapping movement, which produces a sound not unlike that of popping popcorn. These males also are easily seen and heard at the Caño Palma site.

Golden-hooded Tanager

Golden-hooded Tanager. This species is common in the station's yard at Caño Palma.


Collared Aracari


Collared Aracari.

With the banding site well-prepared now, I think I will be back there once or twice before I go. It's a hundred times buggier (mosquitos) than the CCC site, and a bit more rustic, but it also has lots of interesting birds.

Monday, November 15, 2010

Strawberry Poison-dart Frog

Today a few photos of the Strawberry Poison-dart Frog (Dendrobates pumilio), an amazingly beautiful and really quite common little frog from the Caño Palma site in Tortuguero, where I am banding for a few days. This site is a only 20-minute boat ride from the "CCC" site where I had been banding since October 21, but it's very different habitat, with different critters.


Like most poison-dart frogs, its toxicity is derived from its diet (mostly formicine ants). Kept in captivity and fed on arthropods, these frogs lose their toxicity.


They are small and beautiful.


There's also a fascinatingly different bird community here, on which I will report a next time.

Sunday, November 14, 2010

Wasp-mimicking Tiger Moth

Today a photo of a Wasp-mimicking Tiger Moth, Isanthrene crabroniformis, from Tortuguero, Costa Rica. Except for the antennae, it doesn't really look like a moth.


Neither does this one. But this is also a moth, Urania Swallowtail Moth (Urania fulgens) playing hide and seek with another one on the other side of the leaf. These diurnal moths are very common in Tortuguero.

Thursday, November 11, 2010

A very late Sulphur-bellied Flycatcher



















Today the banding session here in Tortuguero, Costa Rica began with rain, which was light when I opened the nets but quickly turned to a downpour that lasted for a couple of hours, which had me close them. For a while, it didn't look like I was going to be able to reopen, but around 10 AM, the rain had stopped, so I opened again.

I did not catch very much, but there was a surprise in the form of this very late Sulphur-bellied Flycatcher. Late because this bird, which breeds from southeast Arizona and Mexico down to Costa Rica but winters in South America, is a common passage migrant in Costa Rica from early August to mid-October (Garrigues & Dean 2007, Stiles & Skutch 1989).



















Precisely because it is so late, it occurred to me that other Myiodynastes flycatchers, perhaps even South American species, had to be carefully ruled out. Streaked Flycatcher is of course very similar to Sulphur-bellied, and does occur in Costa Rica, even winters here (mostly on the Pacific slope, rare on the Caribbean slope). Obviously we need to start with that bird.




















The BNA account for Sulphur-bellied is not very encouraging in this respect, for it claims that Streaked Flycatcher is "often not readily distinguishable in the field". It goes on, however, to list distinguishing field marks: "Streaked is larger with a more robust bill [...], that has extensive pale area at base of lower mandible (dark only on distal half), a narrower dusky malar streak that rarely meets across the chin, which typically is whitish on Streaked and blackish on Sulphur-bellied. [Streaked also with] yellowish-tinged supercilium and mustachial stripes (unlike Sulphur-bellied). [...] Sulphur-bellied also has coarser streaking on underparts; (often) brighter yellow on belly; grayer, less tawny crown; and more whitish edgings on wing coverts (lacks rufous or buff edgings)" (Lowther & Stotz 1999).

With the very notable exception of the coloration of the lower mandible, everything here fits our bird.  While holding the bird in the hand, I noticed the light but extensive yellow on the belly, the dark malar stripe, and the whitish (not creamy) supercilium. For me, it was a Sulphur-bellied Flycatcher. At this point, I was still unaware of a reputed difference in the lower mandible.

But practically every field guide mentions it!

Howell & Webb (1995): "Sulphur-bellied Flycatcher has smaller bill [than Streaked Flycatcher] with little or no flesh below at base."

Stiles & Skutch (1989): "Sulphur-bellied Flycatcher has darker bill, chin and malar area than Streaked Flycatcher, with belly at least as yellow as breast."

Garrigues & Dean (2007): "Streaked Flycatcher very similar in appearance to Sulphur-bellied Flycatcher, but differs in having pink basal half of lower mandible, cream-colored superciliary, thin malar stripe, and whitish belly." (their emphasis)



















Pyle (1997) mentions a measurable difference in bill size, which, had I known about it, I would have checked for on this bird. But I only found out after I let it go. He also mentions differences in the width of the streaks in the outer tail feathers, which are <3 mm wide in Sulphur-bellied and >3 mm wide in Streaked Flycatcher. He concludes with differences in malar stripe and chin color, and again with a color difference on the lower mandible: "lower mandible [of Sulphur-bellied Flycatcher] with an indistinct or no pale base (vs base of lower mandible extensively pale pinkish in Streaked Flycatcher)."

There are three more Myiodynastes flycatchers found in South America, but none of them look like this bird. Only Variegated Flycatcher shares some plumage characters, but that bird has a smaller head and a much smaller bill.

Sticking with Sulphur-bellied Flycatcher vs. Streaked Flycatcher, I believe this to be a Sulphur-bellied Flycatcher. All field marks are good for that species, except the coloration of the lower mandible.

As I was preparing this post, I consulted via Skype with Oliver Komar and Carlos Funes of SalvaNATURA. They looked at my photos and compared them with eight photos of Sulphur-bellied Flycatcher in the SalvaNATURA visual database. Six birds showed some pink at the base of the lower mandible, and two almost none. Clearly, this is a variable character, with my bird today likely at the other end of the spectrum.


12 November 2010 postscript:
Here are some photos from Arizona of Sulphur-bellied Flycatchers, including one photo of an individual with about as much light color on the lower mandible as my bird. 
Two photos of Streaked Flycatcher from Peru with a darker lower mandible can be seen here.

Clearly, this character is variable and should not be used to separate the two species.


Acknowledgments:
Thanks to Oliver Komar and Carlos Funes for commenting on this bird, and for comparing photos of other Sulphur-bellied Flycatcher individuals.

Cited literature:
Garrigues, R. and R. Dean. 2007. The Birds of Costa Rica: a Field Guide. Cornell Univ. Press, Ithaca, NY.
Howell, Steve N.G. and Sophie Webb. 1995. A Guide to the Birds of Mexico and Northern Central America, Oxford University Press, Oxford, England. 
Lowther, Peter E. and Douglas F. Stotz. 1999. Sulphur-bellied Flycatcher (Myiodynastes luteiventris), 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/475
Pyle, Peter. 1997. Identification Guide to North American Birds, Part 1 Columbidae to Ploceidae. Slate Creek Press, Bolinas, California.
Stiles, F. G. and A. F. Skutch. 1989. A guide to the birds of Costa Rica. Cornell Univ. Press, Ithaca, NY.

Tuesday, November 9, 2010

Chestnut-sided Warbler



















Today, I had two Chestnut-sided Warblers side by side in the net. That in itself is not so remarkable, given how common they are here in Tortuguero, Costa Rica, as migrants and winter visitors. I see these birds practically every day, usually a little higher in the canopy. I don't catch them very often.

In fact, since I've been here, I've only caught two individuals before these two. One was on the 21st of October, my first day of banding here. The other was on the 29th of October. That second bird got out of the net on its own, before I could extract it.

What is remarkable about today's capture, however, is that one of the birds was already banded - and it wasn't the October 21 bird! Unfortunately, I don't have access to the banding database of this site, so I cannot yet be 100% sure of this, but I think this may be a recapture from somewhere else!

As you can see when you click on the photo, the band ends in a 6. The full band code was 211094346. I looked at the (paper) banding records going back to 16 October 2010, when Evan Adams started banding here, and I do not find any record of this band. In fact - and here's the kicker - I do not find any 0 or similar sized band records that start with 211!

This last bit of evidence tells me that the series from which this band came is not from here. I aged the bird as a HY (hatch year) bird, based on a molt limit visible in the primary coverts. So, unless I am very much mistaken, this bird was very likely banded somewhere else earlier this year!

If so, it would be a great capture, for this is really why we band birds in the first place. But again, just like the recent putative Bicknell's Thrush captures, we won't know for sure until later. I'll have to check with the site coordinator whether this is really a recapture from someplace else. If so, it will likely take a bit more time before we know where it was banded.

Postscript 24 November 2010:
This bird was banded right here in Tortuguero in October 2008! Not a hatch year bird then; I still need a lot more experience ageing warblers, which is more difficult than, say, thrushes. But the recapture, two years later, seems to imply either winter site fidelity or, at the very least, a preference for using the same migration route among years. A third capture outside migration season would clinch it. But what are the odds of that?

Monday, November 8, 2010

Oops!... I did it again



















I think I caught another Bicknell's Thrush today!

This morning it was obvious that migration was good overnight, for I caught many birds with only a few nets open. The vast majority were Catharus thrushes, with 23 Swainson's Thrushes, 2 Gray-cheeked Thrushes, 1 Veery, and the above individual. For me, this is another candidate for Bicknell's Thrush.



















This bird has no obvious eye ring or supraloral mark, so we can quickly rule out Swainson's Thrush. It's not a Veery either, for it lacks the reddish tone on the upperparts, and has more spotting on the breast than Veery does. It could be a Gray-cheeked, except the colors are a little warmer than on the average Gray-cheeked. Also, it has a buffy wash on the throat, unlike Gray-cheeked. And the wing formula seems better for Bicknell's than for Gray-cheeked. (See also previous post for a discussion of this and other characters.)



















Then if I tell you that the wing cord was 93 mm (almost too short for Gray-cheeked, about average for Bicknell's) and that the tail measured 61 mm (definitely too short for Gray-cheeked but about average for Bicknell's Thrush), I think you see where I'm going with this!

Another thing I noticed on this bird, having read up on Catharus thrushes since last week's intriguing capture, was the color of the legs. Pyle mentions for Bicknell's Thrush "legs flesh with a purplish tinge or a brownish-dusky wash, darker than toes" while his description of the Gray-cheeked Thrush's legs is "pale flesh with a dusky wash, paler than the toes" (Pyle 1997). In the hand, I did see a purplish tinge, and while I didn't take any photos of the legs specifically, I think we can appreciate in the third photo that the toes of this bird are lighter than the legs.

Obviously, this time I did collect a tail feather, and you can see quite well which one it is, from the third photo.

It will very likely be months at the very least before the feather has been analyzed, and we have a bit more certainty which species this is.

Assuming for a minute that both birds really were Bicknell's Thrushes, could it be that this species has been under-reported in Central America? Another, perhaps more likely possibility is that a small percentage of Catharus thrushes cannot safely be identified to species, even in the hand.



















Another surprise find today was this bird, White-throated Thrush. Normally a middle elevations species (like the White-crowned Manakin of last week), not a bird expected at sea level. Like the manakin, this bird is not listed on the checklist included in the banding protocol for the site (Ralph et al. 2008), although both Stiles & Skutch (1989) and Garrigues & Dean (2007) mention post-breeding altitudinal migration in this species.

Cited literature:
Garrigues, R. and R. Dean. 2007. The Birds of Costa Rica: a Field Guide. Cornell Univ. Press, Ithaca, NY.
Pyle, Peter 1997. Identification Guide to North American Birds, Part 1 Columbidae to Ploceidae. Slate Creek Press, Bolinas, California.
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.