Saturday, October 30, 2010

Ageing hummingbirds



















Most field guides mention rufous feather edging on the head and upperparts as a way to tell hatch year hummingbirds from older individuals in many species. Bird banders look for that, but they also look for something not visible in the field: bill striations. The bills of young hummingbirds are soft and often a little shorter (because still growing) than those of older birds. They also show little corrugations or striations - growth marks - along the edge of the upper mandible. Over time, as the hummingbird gets older, the bill gets harder and smoother, and these bill striations disappear.

Thus, the percentage of bill striations can be used to age the hummingbird in the hand. A sufficient amount of such data collected on a resident population of hummingbirds can give us clues about the timing of the breeding season, which in many hummingbird species is timed with the flowering of the species' favorite shrub or tree, and does not necessarily follow the breeding cycle of the majority of birds, which is usually timed around the rainy season in the tropics. Molt data provide additional clues, as most hummingbirds suspend their molt during the breeding season.

The bird at the top is an immature Rufous-tailed Hummingbird, the most common species in lowland areas in Costa Rica, and found from Mexico to western Venezuela. Clicking on the photo will open that photo in your browser window; clicking on it again will blow it up to fantastic detail. I suggest you do this to view the 80% bill striations score that this particular individual shows. A fine line of diagonal marks runs across the edge of the upper mandible. This individual probably hatched less than two months ago.



















Here is another Rufous-tailed Hummingbird, caught at the same location (Tortuguero, Costa Rica) on the same day (October 28th, 2010). This bird shows only 40% of bill striations. From the base of the bill, until almost half of the bill, remaining striations or corrugations can be seen, but this bill is certainly more advanced in the process of smoothing and hardening than that of the previous individual. This bird is probably a hatch year bird also, but likely a few months older than the other bird.



















Here's another species, a Bronzy Hermit. This is also a common species here in Tortuguero, one that I catch almost daily. Click on the photo, then click again, and determine for yourself what the bill striations score in this particular individual would be. I'll tell you what I think it is a little further below. If you accurately scored % bill striations, you're one little step advanced in Hummingbird Banding 101. (And if you're concerned that the bird looks a little stressed, with the tongue hanging out like that, I can tell you that it took off full throttle immediately after this photo was taken. I do have a bottle of sugar water ready to feed a tired hummingbird, but in this case it was not necessary to use it.)



















This is a Long-billed Hermit. The rufous edging of the head feathers (and the rufous in the facial stripes) tells us this is another hatch year bird. About 60% of the bill shows striations.



















OK, so what does an adult bill then look like? Here's an adult male Green-throated Mountain-gem, a highland species from Honduras, photographed September 2010. As you can see, his bill is smooth.



















And finally an adult female of the same species, photographed during the same banding pulse, with less than 10% bill striations at the base of the bill. Some adults will retain up to 10% of bill striations.

The Bronzy Hermit (third photo from the top) shows about 40% bill striations, although the quality of the photo makes it hard to assess.


Postscript (nicely tying this and the previous post together):
The cadaver of the young hummingbird that the snake tried to eat a couple of days ago, shows something you'll never see on a hatch year temperate zone breeder: symmetrical wing molt. The bird was molting P9 in both wings. Symmetrical wing molt is a feature usually taken as indicative of an AHY (after hatch year, i.e. adult) bird. This hummingbird, however, also shows 50% bill striations, and therefore must be a HY bird. This is just one example of many where tropical birds defy our general notions of birds, largely based on temperate zone breeders. There still remains a lot to discover!

Friday, October 29, 2010

Green Vine Snake



















Parental Advisory: the following blog entry contains graphic images of animal violence!

This beautiful snake is a Green Vine Snake (Oxybelis fulgidus), and is common in Tortuguero, Costa Rica.

I found it today in one of the nets as it was trying to eat a hummingbird!



















When I found it, the hummingbird was already dead. I do net runs every half hour, but I was too late for the juvenile Rufous-tailed Hummingbird that the snake is trying to eat here.



















Hummingbirds are often less entangled in the nets than other birds, and the snake certainly had a chance of picking it out of the net, just as the hummingbird had a chance of flying out.




















But the poor little hummingbird was stuck in the net and couldn't get out; for the same reason, the snake couldn't eat it.



















These snakes can get over 2 m long. This individual was about a meter and a half.

Man of the hour Walt Sakai got the snake out of the net. I had no idea if this thing was going to be poisonous, so I exercised the necessary caution. Next time I find one in the nets, I'll remove it myself.

I do net runs every half hour here, which is more frequent than at many other banding stations, mainly to prevent birds from overheating should they get caught in a sunny spot. Apparently, other dangers are lurking too. This is the first bird that died during my time here. I hope it will be the last also.

Wednesday, October 27, 2010

Green Turtle hatchling



















Eco-tourism is big business here in Tortuguero, Costa Rica. Massive numbers of eco-tourists roam the T-shirt shops by day, and come out on the beach around sunset. Most people who come here, do so to see this: a baby Green Turtle, Chelonia mydas. Tortuguero is one of the most important breeding areas for this species of sea turtle, and most of the Caribbean population hails from only a few beaches in Tortuguero.



















At night, female turtles emerge from the sea to lay their eggs in holes they dig on the beach. They carefully cover up their brood, and return to the sea. The eggs will hatch after about 60 days or so, and the hatchlings then dig themselves out and head to the water. This usually also happens at night, to avoid predators, as well as hot sand, as much as possible.



















When I found the hatchling late yesterday afternoon, it was half hid in a small pit of sand. Three Common Black Hawks, including this juvenile, were eyeing it. Hatchlings have to make the 15 - 20 m journey to sea trying not to get eaten by tiger herons, black vultures, crabs, and apparently also black hawks. I decided to escort it a little.



















Made it!

Once they reach the sea, however, they are still not safe and I'm sure a fair number gets picked off by Magnificent Frigatebirds. The Green Turtles themselves, unlike most sea turtles but probably like many eco-tourists, are vegetarians.

Postscript 19 November 2010
I was not previously aware of this, but Green Turtle hatchlings need to be left alone and should not be picked up. Even though the journey across the beach to the ocean is only 25 m, they need to make that journey on their own, as imprinting of the beach's tactile qualities may help them remember it as adults later on. Had I known this, I would not have picked up the hatchling.

Tuesday, October 26, 2010

Bats



















This little leaf-nosed bat with a stripey face is a Common Tent-making Bat, Uroderma bilobatum. It is common in Costa Rica at low and middle elevations, and roosts in "tents" constructed out of palms and other plants. Very likely I have a roost of them near to where I'm mistnetting for birds, for several mornings in a row now I've had these guys in the nets.



















In the nets they squeak loudly and can quickly get themselves in a real tangle. The thing is to check right away and get them out before they've had a chance to get real tangled up.They have sharp teeth and will bite readily; I try to get them to bite the bird bag so they won't bite me.



















Today I opened at sunrise; evidently I need to wait a little until after sunrise, for I still caught three individuals.



















A few days ago I photographed these Proboscis Bats, Rhynchonycteris naso. They are small and usually found near water.



















A single male will usually have a harem of females around him. This group had ten individuals.

Monday, October 25, 2010

Mini-wave of Gray-cheeked Thrushes



















As my regular blog readers know, I've just started bird banding in Tortuguero, right on the Caribbean coast of Costa Rica last week. Today we had an early-morning mini-wave of Gray-cheeked Thrushes. We had five graycheeks in the first two net runs, then two more plus a recapture later in the morning.



















According to Stiles & Skutch (1989), Gray-cheeked Thrush is a "very uncommon fall migrant (early October - mid-November), mainly on Caribbean slope and to ca. 5000ft (1500m) in central highlands". I suspect that the species' secretive habits obscure its actual presence, although they are certainly less common than Swainson's Thrush, which even today eventually outnumbered it.



















The bird shown here was caught a few days ago.

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

Sunday, October 24, 2010

Bare-throated Tiger-heron

Today a picture of a juvenile Bare-throated Tiger-heron on the beach. It's a common bird here in Tortuguero, Costa Rica. Adults have blueish gray heads and upperparts, with finer barring, while juveniles are brown all over and more coarsely barred.

This morning, over breakfast, one of the sea turtle interns asked me about a bird that she saw eating turtle hatchlings on the beach. From her description, it sounded like the suspect was a tiger-heron.

After breakfast, I walked a bit on the beach and saw turtle hatchling tracks and what could be tiger-heron tracks in the sand...

Thursday, October 21, 2010

Arrived in Tortuguero

Yesterday I arrived in Tortuguero, Costa Rica, to band birds at the longest running bird banding station in Latin America. Tortuguero is world famous as a breeding site for marine turtles, but turtles are not the only creatures living there. In fact, the place is teeming with wildlife of all sorts - including snakes!

A very common, no - abundant - snake here is the Eyelash Pitviper. Highly poisonous, and responsible for many fatalities each year in Costa Rica. This, of course, is not it. What I'm holding here is just a cute little baby Boa Constrictor, completely harmless. Well, maybe not completely. I was advised not to harass it in any way, or it might just start constricting my arm. So I didn't, and it didn't.

The gardener of the CCC (Caribbean Conservation Corporation), which is where I'm staying in Tortuguero, found this individual. Isn't it just beautiful?

Birds this first day were mostly Swainson's Thrushes, Empidonax flycatchers, wood-pewees, and Great Crested Flycatchers. Those guys are here in pretty good numbers. Some of the resident species we caught today include Northern Barred Woodcreeper and a female White-collared Manakin.

The manakin had a bill deformity. Poor thing.

Postscript 7 December 2010:
The circle comes round in this last week for me in Tortuguero, as I caught again one of the first birds I banded here: that White-collared Manakin with the bill deformity. It is well-known from the literature that birds with bill deformities can often be infested with quantities of ectoparasites. Grooming one's plumage, after all, is harder with misshapen equipment. So is feeding, and thus the bird is often at a significant disadvantage. This particular individual, however, seems to be coping just fine. On 21 October, she weighed 16.7 g and had a 0 fat score. Now, 47 days later, I measured 17.5 g for body mass and 2 for fat score!

Monday, October 18, 2010

The Birdathon

It's over, and what a birdathon it was! Oliver's team, of which I was part this year, put in its best performance ever, ending with 208 species! Undoubtedly favorable weather was a factor in this success. Even though we missed several common species, we also found many birds that are harder to get, including even a new species for the country! Our team, which consisted of Oliver Komar, Benjamin Rivera, Roselvy Juárez and myself, birded western El Salvador for 48 hours. Exhausting as it was, it was also great fun and 100% worth the effort.

The bird at the top of this post is a female Great Curassow, one of four endangered bird species found in El Salvador. We got this bird Sunday morning in National Park El Imposible, the only place in El Salvador where this species is found.

La Hachadura
We started Saturday morning at daybreak in the fields near La Hachadura, a village on the border with Guatemala. Off to a good start, we got many target species here, as well as a few unexpected ones. Before breakfast, we got Double-striped Thick-knee (17 individuals, one pictured above), Solitary Sandpiper (4), Wilson's Snipe (4), and that 'new' species for the country: Purple Martin. Actually, I thought I saw and photographed a Purple Martin a few weeks ago in National Park Walter Deininger, which I wrote about here. At the time, I didn't think too much of that sighting, until Oliver alerted me to the fact that this species has not yet been documented to occur in El Salvador. Saturday morning, in much better light, we saw an adult male followed by a male and female fly over. I got a photo of that male, but the photo came out as a blur and identification is not possible from that photo... This time, however, the observers made the identification in the field and were in complete agreement that it was this species, and not the slightly smaller, differently-plumaged resident species Grey-breasted Martin (which we also saw).

Barra de Santiago
We had breakfast in Barra de Santiago and then were off searching for birds in the mangroves there. We encountered many mangrove specialties such as Rufous-necked Wood-Rail, Boat-billed Heron, Mangrove Vireo, Mangrove Swallow, and mangrove subspecies of Common Black Hawk and Yellow Warbler. Other notable observations in the mangroves include Grey-necked Wood-Rail, and a cluster of three singing (!) Black-and-white Warblers.

The mudflats at Barra de Santiago had Snowy Plover, Wilson's Plover, Collared Plover (the bird in the standard blog header, at the top right), Semipalmated Plover, Black-bellied Plover, American Oystercatcher, Marbled Godwit, Short-billed Dowitcher, Greater Yellowlegs, Black-necked Stilt, Least Sandpiper, Sanderling, as well as Sandwich, Royal and Elegant Terns, Laughing and Franklin's Gulls, and various other species. Part of the heroics of a birdathon is unexpected adversity, which we encountered in the form of a flat tire we had to replace. That done, we debated whether we should drive over to Los Cóbanos and rent a boat to go out on the ocean there, or try to arrange something from Barra de Santiago. Pressed for time, we chose the latter option.

We went out on the ocean in a small wooden fishing boat, which had some trouble breaking through the considerable surf. Once that was accomplished, however, we went out on a calm Pacific Ocean, in search of pelagics. About a kilometer out, we visited some fishing boats but they only had species that we had already seen from land, like Magnificent Frigatebird and Brown Pelican. We knew we had to go out further to encounter the truly pelagic stuff, but also knew that this was virtually impossible with only a few hours in a wooden fishing boat. However, as we got a little further offshore, we began to encounter specialties like Brown Noddy, Pomarine Jaeger, Black Storm-Petrel, and groups of Red-necked Phalaropes.

We also saw a couple of sea turtles. Intriguing was a sighting of a group of about 20 smallish birds that took off and flew rapidly away from us. We tried to follow but lost them almost immediately and never relocated this group. I was at the bow of the boat and turned around to say "Wow, what were they? They looked like alcids to me." To which Oliver replied that he too had been reminded of alcids! The boatsman merely said they were different from the omnipresent Red-necked Phalaropes, and that he had seen this particular species before. And that too, of course, is a classic part of birdathon lore: 'the ones that got away...'

Around nightfall, we picked up nightjars like Common Pauraque and Chuck-Will's-Widow, before heading back to our lodging in El Imposible.

El Imposible
All Sunday morning and a good deal of Sunday afternoon we spent in National Park El Imposible, where again we found many great birds, like Crested Guan, Great Currasow, King Vulture, Black Hawk-Eagle, Blue Seedeater, Blue Bunting, Paltry Tyrannulet, Eye-ringed Flatbill, Bright-rumped Attila, Long-tailed Manakin, Long-billed Gnatwren, and many, many others.

This Pale-billed Woodpecker belongs to the same genus as the now extinct Ivory-billed Woodpecker, and also produces a 'double rap', like the ivorybill once did.

One of the highlights for me personally was the bird pictured above. A few weeks ago, I was interviewed by Charlie Moores for his birding and conservation podcast called Talking Naturally about the birdathon and the bird monitoring program it sponsors, and one of the things he asked me was "which bird would you like to see more than anything else in the birdathon?" My answer was White Hawk, a spectacular raptor that is found in El Imposible but had thus far eluded me through several visits. As we reached the lookout of Cerro Leon to pick up raptors, Benjamin spotted a white speck sitting in a tree on the opposite mountain slope. The bird sat there for a few minutes while I tried taking photos of it, then took of, circled a bit and left. Had we reached the lookout ten minutes later, we never would have gotten this fantastic bird.

Santa Rita
We got to Santa Rita later than we had hoped, and found fewer species than expected, although a late Sulphur-bellied Flycatcher, one of the few species that breed here and migrate to South America, was a great find. Also there was this Boat-billed Heron, a species we had already found the day before in Barra de Santiago. In Barra, I couldn't get any decent photos. In the fading light at Santa Rita, this individual was more cooperative.

If you've enjoyed reading all of this, and you think bird conservation in Central America is a worthy cause, then please consider sponsoring the birdathon with a donation! All funds raised are used for bird monitoring at various banding stations in El Salvador and Honduras. Instructions on how to donate, and more information about the event and the program it sponsors, can be found here. Your support is greatly appreciated!

Friday, October 15, 2010

Birdathon weekend!

We're only hours away from the event that I have the honor of organizing this year, SalvaNATURA's 8th Annual Birdathon! This weekend, five teams will visit a number of sites all over El Salvador, trying to find as many bird species as we can. The event is a fundraiser for bird conservation in El Salvador and Honduras.

My team, which includes Roselvy and Oliver, will visit Barra de Santiago, Parque Nacional El Imposible, Santa Rita, and, if we have time, Los Cóbanos. All these sites are in western El Salvador.

We hope to find around 200 bird species, including the Common Tody-Flycatcher, pictured above.

If you haven't already been over there, please visit the birdathon blog for more information about the event, including instructions on how to sponsor it.

Common Tody-Flycatcher is a tiny bird that's found in edge habitats like garden, plantations, second growth and forest edges. This individual was at the edge of the mangrove forest at the Bocana Rio Jiboa, El Salvador, last week.

Monday I will report which birds we saw this weekend. Then Monday night, I will travel to Costa Rica, where I will be banding birds for a couple of months. Stay tuned...

Monday, October 11, 2010

Dots

A couple of posts ago, I grumbled about having seen so little hawk migration thus far in El Salvador.

Last Saturday, Roselvy and I went to a Maya archaeological site called San Andrés, in the Valley of Zapotitán, more or less halfway between San Salvador and Santa Ana. Here, we found beauty, tranquility and, atop "Estructura 4", a 360° view of the sky.

Structure 4 is the hill on the far right in this picture, behind the little tree. The other three hills are Structures 1, 2 and 3, which are off limits. Although not as impressive as Tikal in Guatemala or Copán in Honduras, San Andrés is an interesting place to visit, with remains of human habitation dating back 3000 years. Situated in the Central American Volcanic Belt, its history is one of settlements establishing themselves, growing, flourishing, and then being wiped out by a volcanic eruption, before the whole process starts again.

Between 10 AM and 4 PM, we watched thousands of raptors, mostly hawks and vultures, stream high overhead. In the morning, the flight was dominated by Swainson's Hawks, which can be seen in the picture at the very top. A few broadwings are also visible in that photo.

Turkey Vulture and Broad-winged Hawk were the other two abundant species, both of which can be seen in this picture if you click on it. The hawk on the left is something else, and if you want to try and identify it for yourself, go right ahead. I'll tell you what it is a little further down in this post.

In the afternoon, the flight was dominated by Turkey Vultures, with thousands streaming over. Scattered among them were Broad-winged Hawks, eight of which can be seen in this picture.

Other migrant hawks we noted were Zone-tailed Hawk (2), Mississippi Kite (12), American Kestrel (1) and Sharp-shinned Hawk (1). With non-migratory, resident raptor species Northern Caracara, Short-tailed Hawk and Roadside Hawk, we got to 11 diurnal raptors, two vulture species included. The 'mystery hawk' in the third photo of course is a Zone-tailed Hawk. Only superficially similar to Turkey Vulture, the bird stands out as different from TV's in a number of ways: wingtips pointier and swept back, tail longer and thinner, head bigger. In this photo, the zone-tail looks a lot smaller than the Turkey Vultures, but that's partly because it is flying higher.

To get a sense of where we were seeing all these birds, here is a relief map of western El Salvador. Right in the middle, below a small crater, is San Salvador. The crater belongs to Volcán de San Salvador. The two yellow cards halfway between that crater and a crater lake, called Lago Coatepeque, identify two archaeological sites, one of which is San Andrés.

We saw birds flying mostly due east, which would bring them a little north of Volcán de San Salvador. I posted our sightings to the national birding listserv here in El Salvador, and this yielded a couple more descriptions from people who had seen the same thing.

Sunday, October 10, 2010

Agonistic behavior in Semipalmated Plover

Late Friday afternoon, I shot a video of a Semipalmated Plover behaving agonistically toward a conspecific on the beach at the mouth of the river Jiboa, on the Pacific coast of El Salvador. Although originally nearly two minutes in length, I edited the video for 'postability' on line.

video
In itself, aggression between Semipalmated Plovers is not that unusual. However, according to the literature, conspecific agonistic behavior is rare in Semipalmated Plover on the wintering grounds. Adam Smith and Erica Nol studied winter foraging behavior and prey selection of the Semipalmated Plover in coastal Venezuela and found that "neither sex exhibited territorial behavior" (Smith & Nol, 2000). Two other researchers also studied the Semipalmated Plover on the wintering grounds in Venezuela, and found that "time devoted to aggression was very low" (Morrier & McNeil, 1991). They did find a significantly higher 'time-aggression index' in October, as compared to the rest of the winter season, and cite other sources that mention agonistic behavior at migration stop-over sites.

If true, why would Semipalmated Plover exhibit such behavior more in migration, and less on the wintering grounds?

Well, assuming that perceived food scarcity drives agonistic behavior, perhaps a wintering plover, having had more time to familiarize itself with local food resources, might be less territorial than a less well-informed migrant passing through, or a recent arrival?

Cited literature:
Morrier, A. & McNeil, R. (1991) "Time activity budget of Wilson's and Semipalmated Plovers in a tropical environment", Wilson Bulletin 103 (4): pp. 598 - 620.
Smith, A.C. & Nol, E. (2000) "Winter foraging behavior and prey selection of the Semipalmated Plover in coastal Venezuela", Wilson Bulletin 112 (4): pp. 467 - 472.

Monday, October 4, 2010

Orange-chinned Parakeets

Today a closer look at a small tropical psittacid, the personable, cheerful, yes downright boisterous Orange-chinned Parakeet. This bird is common in tropical dry forest and heavily degraded habitats - towns, cities - from western Mexico all the way through Pacific Slope Central America to Colombia and Venezuela. It's certainly common throughout the city of San Salvador, and I often see them in the yard outside my building.

And that's where these photos were taken today.

Like many other species in the genus Brotogeris, Orange-chinned Parakeets (Brotogeris jugularis) are popular in the pet trade. Researching them a little, I came across an internet site on which captive-bred individuals of this species were offered for $350 a piece, and were recommended for making excellent companion birds.

Sadly, down here in El Salvador, where most people see wild parrots fly around every day, the general public also think of them primarily as cage birds. Two species are very common and easily seen, at least in San Salvador: this one, and the Pacific (or Green) Parakeet, which is considerably larger. I wrote about a Pacific Parakeet roost in Antiguo Cuscatlán, one of the larger neighborhoods here in San Salvador, back in June. I've been thinking to revisit that roost, because lately I've noticed much higher numbers of Pacific Parakeets flying toward it at dusk than in June. Sometimes one can find a few similar-sized Red-throated Parakeets among the thousands of Pacific Parakeets visiting that roost. These small Orange-chinned Parakeets do not sleep there; they have smaller roosts all over town.

All ages and sexes look similar, so there's no way of knowing if this particular bird is a male or female, young bird or adult.

Only from certain angles is the orange chin visible.

Since they have been popular as pets for such a long time, their behavior has been relatively well studied. For example, an utterly charming science paper from 1938 describes "left-handedness in parrots" (Friedmann & Davis 1938). Yes, parrots apparently are - like me - for the most part 'left-handed'; that is, they tend to pick up food items with their left foot. The two authors tested twenty individuals representing fifteen different species, and studied how these twenty birds grabbed food items presented to them in a zoo - for each individual twenty times! For the group as a whole, they found a 72.2% score of 'left-handedness'. However, all three participant Orange-chinned Parakeets had a score of 100% - that is, twenty out of twenty times that each of them picked up a food item, they used their left foot!

The two birds in the photos here did not need to pick up anything with their feet. They fed by just bending over and cracking seed after seed with their powerful bills. However, knowing about this 'left-handedness' thing now, I'll definitely look at psittacids differently from now on.

Cited literature:
Friedmann, H. and Davis, M. 1938 "Left-handedness" in Parrots. The Auk, Vol 55: 478-480.