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.

Friday, December 19, 2014

Nocturnal Creatures (Part I: Pacific Screech-Owls)

Dusk falls quickly in the tropics, and with it comes a rapid transition between the activities of the diurnal and nocturnal fauna.  As darkness falls, the daytime animals take advantage of the last few minutes of fading light.  The last of the day's hummingbirds fill their stomachs with nectar before calling it a night; the howler monkeys bellow one last claim on their territories; and flocks of Tennessee Warbler settle in to roost, nudging and shouldering each other to vie for the best spot on the branch.  Around this time there is a small window, just before the real darkness sets in, in which the bats and owls leave their daytime roosts and begin their nightly routines.  These are the creatures to whom the night belongs.

© Tyler Christensen
Pacific Screech-Owls (Megascops cooperi, above) are perhaps the most common owls in Costa Rica, much like our Eastern Screech-Owls (Megascops asio) at home in New Jersey.  Both species are flexible in their habitats and diets, making them well-suited to thriving in areas with human habitation.  I photographed the owl pictured above on the grounds here at Finca Pura Vida just a few evenings ago.

For the past few nights we have been capturing owls for our research, applying the same method I used during Washington Crossing Audubon Society's Saw-whet Owl Migration Survey.  This method involves the use of several mist nets and an electronic audiolure that plays the male vocalizations of the owl species being targeted.  Ever curious, owls often come in to investigate and wind up in the nets.

© Tyler Christensen
Various research projects require the capture of owls for study.  Ours involves deciphering patterns by which these birds replace their feathers, and whether these patterns can be used to discern the age of a bird in question.  While this research may not be universally interesting (I can think of several people off the bat who were visibly regretful after asking for more detail), I do think we can all appreciate the spectacular encounters that happen to go along with it.

You cannot catch owls here without also catching bats, and catch them we did -- indeed, some were as large as the owls themselves.  Our encounters with these bats will be the topic of Part II of this post.

Monday, December 15, 2014

Herpetofauna of the Nicoya Peninsula

Our primary objective while were here in Costa Rica is focused on ornithology research, but that doesn't mean we don’t delve into other subjects.  Much is still unknown about the distribution and abundance of reptiles and amphibians here on the Nicoya Peninsula .  Over the past few years we have taken a lot of notes and data points on where we have found various species of snakes, lizards, frogs, and turtles across the Peninsula.   
As we've been going along, I've been using the Meet Your Neighbors photo studio technique to isolate subjects on completely neutral backgrounds. It serves a dual purpose of having very clear record shots, and also will hopefully go into a guide of sorts for the herpetofauna for the Peninsula at some point. 
Our first day came with an interesting discovery -- On our way from the ferry to the Finca, Tyler spotted something sliding back and forth across the road: a Green Ratsnake  (Senticolis triaspis). This Colubrid is in the same family as our Black Ratsnake at home, and they share very similar behavior and diet. 

Green Ratsnake  (Senticolis triaspis)  

Later on in the first night as we were walking around the Finca, Tyler spotted something on the side of one of the buildings. It was a large frog, apparently scanning the property from a high perch. We quickly grabbed a butterfly net and lowered him down for identification.  It turned out to be the ever-interesting Common Milk Frog (Trachycephalus venulosus). These frogs can secrete a noxious mucus-like chemical from their skin when disturbed.   

Common Milk Frog (Trachycephalus venulosus) 

The latest species we encountered was Costa Rica's poster-child of fauna, the Red-eyed Tree Frog (Agalychnis callidryas).  We had heard them in the past at the Finca, but could never locate them. The other night, we set out on a mission to finally locate them and get photographic documentation. After what some might call an intrepid adventure, we located between 6-7 individuals.  As you can see, it was well worth it -- "charismatic" doesn't even begin to describe these frogs. Interestingly enough, they are very variable in coloration, depending on if you’re on the Pacific or Caribbean side of Costa Rica.  The frogs from the Caribbean side are more colorful, but the Pacific variant has their own unique charm. 

Red-eyed Tree Frog (Agalychnis callidryas)

Thursday, December 11, 2014

Warm Greetings

A trio of Mangrove Swallows (tropical relatives of our Tree Swallow) was swirling behind the ferry that crosses the Gulf of Nicoya, showing off the impressive aerobatic skills shared by all members of the swallow family.  Brown Pelicans travelled low in formation over the water.  Magnificent Frigatebirds, fork-tailed and long-winged wanderers of the open ocean, circled higher, watching and waiting to steal the hard-fought-for meal of a Laughing Gull or Royal Tern.  The occasional Brown Booby would cross in front of the ship.

Brown Pelicans aboard a small fishing boat in the Gulf of Nicoya

Our arrival in Costa Rica yesterday marks the beginning of the fourth annual research expedition of the Nicoya Peninsula Avian Research Station.  In each of these four years my research partner Sean Graesser and I have traveled to the Nicoya Peninsula of the northwestern portion of the country to collect important data on some of the more vulnerable species of neotropical migratory songbirds, which spend their winters here.  Over the next seven weeks we will run several bird banding stations to capture, mark, and study these long-distance migrants, and to collect data from individuals that we banded in the past that have returned.

The sun was going down as we turned down the dirt road that leads to Finca Pura Vida, the farm on which we will live for the next two months.  As we tried (in vain) to dodge the myriad potholes, two bird calls familiar to us northerners came through the open windows: the "stchip" of a Yellow Warbler and the “kinkachurr” of a Summer Tanager.  I welcomed these as warm greetings to our return to Costa Rica.  It’s good to be back!