Monday, January 4, 2016

Consortium of Color

Every bird has a consortium of proteins and pigments in their feathers that work together to produce a pattern of colors.  The birds that we catch during our studies on the Nicoya Peninsula demonstrate the astonishing variety of patterns and colors that makes tropical birds famous for their good looks.  This winter I have been taking macro photos of the plumages of some of the more ornate birds we encounter at our banding stations.  Without delving into the explanations behind the production of these patterns and colors - a topic for a different post - I take this opportunity to share some of the most stunning (at least by human standards) plumages we encounter.
Male Barred Antshrike
Turquoise-browed Motmot
Rump and central tail feathers of a male Black-headed Trogon
Crown feathers of a male Long-billed Starthroat
Gorget of a male Long-billed Starthroat
 Below are photos of each of the birds featured above, in order of appearance.  


Tuesday, December 22, 2015


Despite Costa Rica having a relatively well-studied bird fauna, our five years of field work on the eastern Nicoya Peninsula have yielded many surprising discoveries.  Among the most interesting are our encounters with bird species which, according to the literature, are not expected to occur on the Nicoya Peninsula at all, or at least during the period we visit each year.  Our most recent three-day banding session at the Reserva Natural Absoluta Cabo Blanco provided several examples of how even our basic knowledge of bird distributions needs quite a bit more work.

One species whose capture this morning represented our fourth encounter is the Ruddy Quail-Dove (Geotrygon montana).   The species' Costa Rica distribution as described by The Birds of Costa Rica (by Richard Garrigues and Robert Dean) and BirdLife International ( extends northward along the Pacific coast only to the Rio Tárcoles.  The Tárcoles lies directly east of the Nicoya Peninsula on the mainland.  A literal (albeit small) gulf separates our encounters of this species with its described distribution.
Female Ruddy Quail-Dove (Geotrygon montata) banded on December 22
Male Ruddy Quail-Dove spotted in January 13, 2014
Another bird encountered this morning that is much more familiar to us North American bird banders is the Wood Thrush (Hylocichla mustelina).  The literature describing the winter range of this species in Costa Rica is incongruous; the most recent edition of The Birds of Costa Rica, depicts the species as being absent from the Nicoya Peninsula, while several reputable sources have published that the species is absent from the Pacific Slope of Costa Rica altogether.  A few other sources (including BirdLife International) correctly include the Nicoya Peninsula in their maps of this species' distribution.  To date we had captured 18 Wood Thrushes at our three banding sites on the Nicoya Peninsula, and today Cabo Blanco produced an additional three. 
Two Wood Thrushes banded on December 22 at Cabo Blanco
Finally, instead of a spacial discrepancy, we have a temporal one; the Swainson's Thrush, according to the most recent edition of The Birds of Costa Rica (Garrigues and Dean, 2014) and the original A Guide to the Birds of Costa Rica (Styles and Skutch, 1989), does occur throughout most of Costa Rica, but only as a passage migrant.  They are said to pass through Costa Rica on their southbound migration in September-November and again on their northbound migration in March-May, but are supposedly absent in December, January, and February.  Apparently the Swainson's Thrush we captured this morning at Cabo Blanco had not read those books, nor had the 17 others we've captured since the project began in 2011.
NPARS's first Swainson's Thrush, banded in 2011
These three species captured this morning are on a list with several other out-of-range or otherwise unexpected bird species that we have encountered since the start of this project.  We find it amazing that even in a country so well-studied (speaking relatively and from a biological perspective), there is still so much to learn about the basic biology of its bird fauna.  We are truly privileged to work in a place with so much to discover.

Tuesday, December 15, 2015


After nearly a year away (and apart), the NPARS team is back together for another month-and-a-half of field work in the tropics.  This winter field season represents the fifth consecutive year of bird banding and research our first trip in 2011.  As we get settled in, we will periodically post updates of our field work, as well as anecdotes about living and working in the tropics.

This post is the first of several of the latter type.

Quite easily the best 'welcome back' we receive upon our return to the Nicoya Peninsula is the hummingbird spectacle at Finca Pura Vida.  The scene is chaotic and mesmerizing, involving hundreds of hummingbirds of nearly a dozen species buzzing around the feeders with dizzying speed.  I recorded the following video in 2014 of the feeding frenzy at Finca Pura Vida:

The main function of the feeders is to facilitate the capture of large numbers of hummingbirds for our research, since they provide us with sufficient sample sizes of these normally seldom-captured birds.  The hummingbird frenzy, however, has become as much a part of life here as the humidity.  Every day, from dawn to dusk, the frantic swarm drones away in the background.  We share a great sense of nostalgia for our hyperactive nectivorous friends, and it has become tradition for us to spend at least a few hours during our first morning back in Costa Rica enjoying and photographing them.

A tree full of Green-breasted Mango (Anthracothorax prevostii)

Male Green-breasted Mango (Anthracothorax prevostii)
It sure feels good to be back!

Tuesday, January 13, 2015

Nocturnal Creatures (Part II: Bats)

My home state of New Jersey (and its neighboring states) proudly boasts nine species of bats; six of these can be found within its borders year-round, while the other three are only with us during the warmer months of the year.

Costa Rica on the other hand has an astounding diversity of bats; to date, the list consists of 111 species!  This is more than all other Costa Rican mammal species combined, and is more than twice the number of bat species found in all of North America -- not bad for a country with less area than Lake Michigan!

Lesser Sac-winged Bats (Saccopteryx leptura) in a tree cavity
Our efforts to study neotropical owls (see Nocturnal Creatures Part I) have provided us with the exciting opportunity to get to know some of the many bat species on the eastern Nicoya Peninsula.  Whether we like it or not, setting up nets at night in the tropics inevitably results in encounters with bats.  Luckily, we like that just fine.  Some of the bat species we have captured alongside the owls we are studying have been truly spectacular; indeed, some of them are nearly as large as the owls themselves!

The Greater Spear-nosed Bat (Phyllostomus hastatus),
 the second-largest bat in Costa Rica
When we were on the first net check of our very first night of owl-netting, we approached a net containing one owl and two Greater Spear-nosed Bats (Phyllostomus hastatus, pictured above and below).  These bats are so large that, in the dim light cast by our headlamps on our approach, we thought they were owls!  The two bats had wingspans of sixteen and seventeen inches, just a few inches shy of the wingspan of the Pacific Screech-Owl that had been captured alongside them.

Greater Spear-nosed Bat (Phyllostomus hastatus)
On the opposite end of the size spectrum we have the Black Myotis (Myotis nigricans), which is one of several equally tiny Costa Rican bats in the genera Myotis and Rhogeesa.  The M. nigricans we encountered just a few days before Christmas weighed just 3.5 grams, about the same weight as a Ruby-throated Hummingbird!

The tiny Black Myotis (Myotis nigricans)
With many outwardly similar-looking genera and species, identification of tropical bats can be a meticulous process.  Distinctions between species are often as subtle as differences in the basal coloration of individual hairs or in the arrangement of teeth.  Since this is the first year we have set up nets after dark, it has been a fun challenge to keep up with the sudden influx of unfamiliar bats that need identifying.
The characteristic "gap" (actually filled by two tiny premolars)
between the molars and canines of species in the genus Myotis
Other notable mentions include the Jamaican Fruit Bat (Artibeus jameicensis), the most commonly encountered bat at Finca Pura Vida; the Common Long-tongued Bat (Glossophaga soricina), which we believe to be at least one of the species that visits the hummingbird feeders at night to sip nectar; and the Pale Spear-nosed Bat (Phyllostomus discolor), the second-largest bat we've captured at the Finca.
The Jamaican Fruit Bat (Artibeus jameicensis)
The handsome (?) face of a Pale Spear-nosed Bat (Phyllostomus discolor)
The nine bat species we have netted so far at Finca Pura Vida are only a fraction of those that occur in the area: the nearby Reserva Natural Absoluta Cabo Blanco -- where one of our bird banding stations is located -- has a list of 41 bat species that have been observed there, and that list continues to grow.  Affiliates of the Cabo Blanco Reserve recently conducted a bat survey, identifying bats both in-hand (using mist nets to capture them) and by recordings of their sonar (which, not unlike bird songs, can be diagnostic of particular species).  During this survey they captured a Silver-tipped Myotis (Myotis albescens) -- a species never before recorded in the reserve -- in addition to twenty other species which were already on the Reserve's official mammal list.

We are thrilled to have the opportunity to become more familiar with the nocturnal fauna of the neotropics, most of which are seldom seen by diurnal animals like Homo sapiens.  The demands placed upon these flying nocturnal creatures have driven the evolution of adaptations that render them utterly bizarre and endlessly fascinating, and the chance to see them up-close is just plain cool.

Saturday, January 3, 2015

Following Birds that Follow Ants

Army ants (Eciton burchellii and related species) mean serious business in tropical forests: each day the members of a colony form a large swarm that raids the surrounding forest, stinging to death and dismembering anything small or slow enough to fail to escape.  A passing swarm (which can easily be thirty feet wide and consist of several hundred thousand individuals) creates a panic among the invertebrates of the forest floor, forcing them to come out of hiding and flee.

A swarm is an event of such magnitude that it is clearly audible to human ears.  It consists of the clicks and taps of grasshoppers and crickets attempting to stay ahead of the front, and the ominous hissing of millions of ant legs passing over the leaves of the forest floor.  It is rare that ant-scale events draw the attention of human-sized observers, but when they do, they fascinate us; the mass emergence of periodical (17-year) cicadas and the migrations of monarchs and dragonflies are two prominent examples that regularly make headlines.

As the swarms move through the forest, they remain connected to their stationary above-ground colony by a single column.  The column consists of ants traveling in both directions: those returning from the front of the swarm carrying captured food items, and those leaving the colony having dropped off their booty to return to the swarm.  The video below shows ants traveling along their column.  Ants traveling toward the camera are returning to their colony with food; those traveling away are leaving to rejoin the swarm.

These events attract the attention of certain bird species, which join the front of the swarm to opportunistically capture the invertebrates and other small animals that the ants flush out of hiding. Ant-following birds from the surrounding forest temporarily ignore territorial boundaries and congregate in large numbers to take advantage of the sudden availability of prey.

Northern Barred-Woodcreeper following a trail army ants up a tree trunk
These raids provide unique opportunities to see many birds concentrated at ground-level.  One particularly large army ant swarm occurred nearby the bird banding station at Cabo Blanco late last month, attracting large numbers of Ruddy Woodcreepers, Gray-headed Tanagers, Red-crowned Ant-Tanagers, and Northern Barred-Woodcreepers.  In addition to being an enjoyable spectacle on its own, it was doubly exciting to see that most of the birds present were sporting our aluminum leg bands:

Ruddy Woodcreeper

Gray-headed Tanager
I watched this group of birds for quite a while as the ant swarm moved through the forest.  I decided to fall back when the swarm started down the slope of a steep ravine, and when my tolerance for army ant stings reached its critical threshold.

Thursday, December 25, 2014

Are there Fer-de-Lance on the Nicoya Peninsula ?

 Arguably Central America’s most deadly and widespread venomous snake is the Fer-de-Lance or Terciopelo. It can be found in a wide variety of habitats throughout Costa Rica.  Studies have even shown that it can survive -- and indeed thrive -- in disturbed habitats in close proximity to humans.

Fer-de-Lance (Bothrops apser)
The big "question mark" remains on the Nicoya Peninsula.  Although no confirmed records exist for the region, the thing I've learned over the years is that doesn't stop most people from believing they are here.

I actually still hold out hope that they do occur here; there is certainly suitable habitat at the southernmost tip in Cabo Blanco national park, but so far I have never seen one. I do however have an alternate theory of what people are seeing.  

Lyre Snake (Trimorphodon biscutatus)
 Fer-de-Lance (Bothrops apser)
The Lyre Snake (Trimorphodon biscutatus) is a common enough snake throughout the Peninsula in multiple habitats, and could very well be the infamous Nicoya Fer-de-Lances people are seeing. Here are a few reasons why: they have a very similar pattern - it’s not a distinct "X" pattern like the Bothrops, but it does overall have very similar coloration. Their behavior when first encountered is strikingly similar: in Panama I came upon a Fer-de-Lance moving along a bank side.  When it spotted me it quickly coiled up start rattling its tail on the leaf litter and brought its head up. I have witnessed the Lyre Snake do the exact same thing.  Now unlike the Fer-de-Lance it won’t make as tight of a coil or stay like that for long: they usually try the threatening position then scatter. The tail rattling though is the exact same in both, and for me it’s one of the more compelling similarities. If you only get a quick look the lyre snake will also flatten its head in a similar fashion to a pit viper. Their eyes can also fool you at first glance they can create a very narrow slitted iris similar to a pit viper.

The flat triangle shaped head distinct in Pit vippers.
If you were to take a close enough look though you would notice the lack of sensory pit glands that all pit vipers posses.

Sensory pit glands on the front of a Fer-de-Lance
So for now I’m still very skeptical that Fer-de-Lance occur widespread throughout the Peninsula, but I still very much hold out hope they are here and that I can finally confirm their occurrence here.

Wednesday, December 24, 2014

Big Trees, Kentucky Warblers, and Site Fidelity

La Reserva Natural Absoluta Cabo Blanco -- the Cabo Blanco Absolute Nature Reserve -- was Costa Rica's first national park.  The Reserve celebrated its 50th anniversary last year.  Before the land was preserved, the area was a hodgepodge of private farms and cattle ranches.  Now the 3,000 acres of forest protected at Cabo Blanco are a testament to the impressive speed at which tropical habitats can regenerate: its youth is masked by the presence of gloriously massive trees, including fast-growing giants such as Guanacaste (Enterolobium cyclocarpum) and Ceiba (the genus to which the mighty Kapok belongs).

This forest is the winter home of a number of neotropical migratory songbird species, which is the reason we find ourselves in this wonderful place.  Among them are several species whose numbers are apparently in acutely rapid decline, such as Kentucky Warbler, Worm-eating Warbler, Ovenbird, Wood Thrush, and Swainson's Thrush.  This week we captured all of these species except Ovenbird (although we did manage to capture one at Finca Pura Vida last week).  We also captured and banded two other neotropical migrant warblers: Chestnut-sided and Tennessee.

The most exciting capture of the week was a Kentucky Warbler, not only because of my personal annual sagas trying to spot them in New Jersey, or because they are threatened in the state, but because one of the Kentuckys banded late last year by my team at Cabo Blanco was just recaptured again on Monday, one year and eight days (and about two thousand miles) later.  It was an immature bird at the time of capture, meaning it celebrated its first birthday this past summer, after its first (hopefully successful) breeding season in North America.

Fortunately I keep my photos organized well enough to have located a photo I took of this very bird during last year's research expedition:

Kentucky Warbler when it was originally banded on
December 14, 2013 (© Tyler Christensen)
Same individual as pictured above when it was recaptured
on December 22, 2014 (© Tyler Christensen)
Birds banded in a previous season and re-encountered in a later one are called between-season recaptures, and are not rare occurrences here (at this point about one in ten birds we capture was banded by the team in previous seasons), but we capture Kentuckeys infrequently enough that this was our first between-season recapture of this species.

Recaptures such as this demonstrate winter site fidelity, or the tendency of a bird to return to the same winter territory year after year.  Many of the migrants we capture are site faithful, and recapture rates among our most common migratory species from one year to the next are roughly 18% for Tennessee Warblers, 20% for Prothonotary Warblers, and a whopping 26% for our Northern Waterthrushes!

As several recent studies have shown, winter site fidelity and winter territoriality (which are related) are, in at least certain species, linked to habitat quality - higher-quality habitats often have repeat customers who stake territorial claims within them.

Evidently the forests of the Cabo Blanco nature reserve are agreeable to at least one Kentucky Warbler, who elected to return to spend another winter.  This group of bird banders happens to have made a similar assessment.