Tuesday, 10 November 2020

A Big Day at La Selva Biological Station

I left the cabin in the pre-dawn gloom, eager to watch the sunrise from the swing bridge. This would be my best chance at Snowy Cotinga. And with an entire day free to explore La Selva, I was hoping to encounter over 100 species. 120 was a reasonable goal, I thought, as I wandered down to the bridge.

White-ringed Flycatcher - La Selva Biological Station, Heredia, Costa Rica

One of the first birds that I observed from the bridge was the above-pictured White-ringed Flycatcher. This species looks similar to Rusty-margined and Social Flycatchers, two common birds in much of the Neotropics. However, its closest relatives are three other species of Conopias from South America. The White-ringed has a limited global range. Like its congeners it is mostly a lowland species, but it only ranges from coastal Honduras south to the Chocó region of western Colombia and northwestern Ecuador. White-ringed Flycatchers have a tendency to be somewhat uncommon. They also prefer to perch high up in the canopy, making them more difficult to detect.  Luckily, the swing bridge enabled me to be positioned a little further off the ground, high enough to appreciate the White-ringed Flycatcher at the top of the dead snag.    

Río Puerto Viejo - La Selva Biological Station, Heredia, Costa Rica

A nice variety of parrots, oropendola/caciques, flycatchers and toucans passed by my location. Some, such as this Brown-hooded Parrot, paused for a few minutes to rest in a riverside tree. 

Brown-hooded Parrot - La Selva Biological Station, Heredia, Costa Rica

Luck was on my side this morning. I noticed an intriguing dusky bird perched near the top branches of a distant tree. It was quite far, but identifiable as a Snowy Cotinga! It was in this situation where I wish I had a scope with me to better appreciate the bird, but this was much better than nothing. Cotingas are a type of holy-grail bird for many birders. They are distinctive, usually uncommon or at least difficult to find, and often incredibly beautiful (though a female Snowy Cotinga is probably not the best example of this!). The Snowy Cotinga is a lowland species with a limited range in the Caribbean lowlands of Central America. 


Snowy Cotinga - La Selva Biological Station, Heredia, Costa Rica

My plan had been to bird around the river for an hour or so at sunrise, then meet up with Laura and my parents for breakfast. Following the meal, we would embark on a nice morning hike on some of the forest trails. 

I still had a few minutes to spare before breakfast and so I quickly investigated a portion of the trail that flanks the river. This proved to be a good decision as I immediately heard a Semiplumbeous Hawk calling from somewhere unseen! This was one of my main targets for La Selva, a species I had never bumped into before. Luckily, the hawk began to call again and I eventually spotted it through a gap in the forest. 

The Semiplumbeous Hawk is a scarce forest hawk which often perches quietly in the canopy or forest edge. This species is known to follow groups of capuchin monkeys through the forests, since these primates often scare up lizards or other small reptiles - a perfect meal for a Semiplumbeous Hawk. 

Semiplumbeous Hawk - La Selva Biological Station, Heredia, Costa Rica

On my way back to the research station I came across my mom. Together, we observed a pair of Pale-billed Woodpeckers, and we also retraced my steps to observe the Semiplumbeous Hawk which had remained in the same area. 

The fruiting trees, flowering shrubs and open areas around the main research station proved to be quite attractive with a variety of bird species. Taking half an hour to enjoy a hearty breakfast did not really detract from the day's birding. I think I added around fifteen species to my eBird checklist for the day while enjoying breakfast.

Band-backed Wren - La Selva Biological Station, Heredia, Costa Rica

These Band-backed Wrens were a familiar presence around the research station.  I have to say, the wrens of the Neotropics are around 10 times more interesting than "our" wrens in eastern North America. These huge, boldly patterned wrens are one of my favourites.

Band-backed Wren - La Selva Biological Station, Heredia, Costa Rica

We finished up our coffees and hit the trails, heading across the bridge to the primary forest beyond. We first explored some gardens around the buildings on the far side of the bridge, adding a few species of tanagers to our lists. I excitedly pointed out our first Black-cowled Oriole in a fruiting tree. We all savoured the excellent looks at this beauty!

Black-cowled Oriole - La Selva Biological Station, Heredia, Costa Rica

As I mentioned in a previous post, many kilometers of hiking trails criss-cross portions of the reserve and quite a few of the trails nearest the research station have been constructed with concrete. Covered with a thin layer of moss, this substrate mutes footsteps which makes it easier to sneak up to wildlife before they hear you. 

We came across a few different tinamous on our walk, our quiet footsteps enabling this. Or, perhaps the tinamous at La Selva are just tame! Each one appeared to be a Great Tinamou, not my hoped for Slaty-breasted Tinamou. 

Great Tinamou - La Selva Biological Station, Heredia, Costa Rica

Tinamous are ground-birds that are most closely related to the Australasian ratites (cassowaries, emus and kiwis). They appear superficially like quails or partridges, but this is due to convergent evolution (i.e. two unrelated groups evolving the same thing independently). 

Great Tinamou - La Selva Biological Station, Heredia, Costa Rica

Great Tinamou - La Selva Biological Station, Heredia, Costa Rica

An ant-swarm caused some excitement during our walk. We first noticed steady streams of army ants swarming across the path and soon the telltale chips of antbirds caught our ears. We were positioned at the very edge of the antswarm, but it was heading away from us deeper into the forest. We still enjoyed many excellent sightings including Bicolored and Ocellated Antbirds, Plain-brown Woodcreeper and Northern Barred-Antshrike. 

Black-crowned Antshrike - La Selva Biological Station, Heredia, Costa Rica

A pair of Black-crowned Antshrikes posed at eye-level right beside the trail. Check out that hooked beak - perfect for capturing and devouring large insects (and perhaps, small reptiles). 

Black-crowned Antshrike - La Selva Biological Station, Heredia, Costa Rica

It is impossible to go for a walk in the tropics with Laura without a few interesting herps showing up! Her keen eyes located several frogs such as this Strawberry Poison Dart Frog (Oophaga pumilio).

Strawberry Poison Dart Frog (Oophaga pumilio) - La Selva Biological Station, Heredia, Costa Rica

The temperatures increased as the morning wore on. At least the shade of the mature forest helped mitigate this somewhat, but we really felt the heat of the day advancing when we left the forest for a brief walk on a boardwalk through an open wetland. At this time of year the water table was quite low, meaning that standing water was not present. I was really hoping that this would not be the case since these wetlands can be very productive for herps at night when they have water. 

Several dragonflies were taking advantage of the warm day. 

Red-mantled Dragonlet (Erythrodiplax fervida) - La Selva Biological Station, Heredia, Costa Rica

This next species is called the Amazon Sapphirewing. It is widespread in the lowlands of Amazonia and Central America but is apparently very difficult to come across. These dragonflies spend most of their time in the canopy but they will rarely come down, usually for short breeding encounters during the mid-day. We were very fortunate to see this one!

Amazon Sapphirewing (Zenithoptera fasciata) - La Selva Biological Station, Heredia, Costa Rica

While we are on the theme of invertebrates, here is an attractive jumping spider (identification to be determined). 

Unidentified jumping spider (subfamily Salticinae) - La Selva Biological Station, Heredia, Costa Rica

We began heading back to the research station, happy with the results of our morning walk. My eBird checklist was ticking along nicely; I believe I was over 80 species already. 

Laura and I love exploring on our own when we are in Central or South America. We generally try to avoid hiring guides for both economic reasons and because it takes away some of the thrill of discovery. But we have also benefitted greatly by the many excellent guides that we have bumped into or hired on occasion. On our way back to the research station we passed a local guide with her clients and she waved us over. She had found a mother and baby Brown-throated Three-toed Sloth!

Brown-thr. Three-toed Sloth (Bradypus variegatus) - La Selva Biological Station, Heredia, Costa Rica

Young sloths will stay with their mother for up to five months after birth, though they are fully weaned after only four or five weeks. Presumably, this is so that the young has time to learn the ways of the forest - which leaves are the best to eat, for example. Sloths are generalists that feed on leaves from a variety of trees, though certain species are preferred. 
 
Brown-thr. Three-toed Sloth (Bradypus variegatus) - La Selva Biological Station, Heredia, Costa Rica

We thanked the guide for generously calling us over and went on our way. As we crossed the bridge I noticed that there was a hawk and vulture flight commencing.

Turkey Vultures - La Selva Biological Station, Heredia, Costa Rica

Central America acts as a natural chokepoint for hawks migrating between North and South America. The middle of March is peak raptor migration time in Costa Rica.  Turkey Vultures were the dominant species and I counted around 1100 in half an hour or so of watching before the flight line changed, no longer being overhead. In addition, some small flocks of Broad-winged and Swainson's Hawks went over. 

Swainson's Hawk - La Selva Biological Station, Heredia, Costa Rica

After lunch my parents and Laura decided to take it easy for a bit. I relaxed for an hour or so as well, but the call of the birds drew me back outside. 

Scarlet-rumped Cacique - La Selva Biological Station, Heredia, Costa Rica

I had found most of my target birds at La Selva but there were two somewhat regular species which I still "needed". These were the Canebrake Wren and Nicaraguan Seed-Finch, two birds that have limited ranges on the Caribbean slope of Central America. I walked back down the entrance road of the research station, my destination being some weedy fields where the Nicaraguan Seed-Finch had been noted in recent weeks.  The walk out was fairly quiet, this fantastic Scarlet-rumped Cacique being the only appreciable highlight. 

Scarlet-rumped Cacique - La Selva Biological Station, Heredia, Costa Rica

I found the gravel road and associated fields where the Nicaraguan Seed-Finches and Canebrake Wrens are sometimes found. Early afternoon, however, is a difficult time to find birds, and the winds had picked up slight as well which complicated matters. My main targets remained silent but I enjoyed picking through flocks of seedeaters while raptors and migrant swallows passed by overhead. Two Great Green Macaws also passed by. Like all macaws, they are usually heard long before they are seen.

Gray Hawk - La Selva Biological Station, Heredia, Costa Rica

Eventually, my ears picked up the distinctive vocalizations of the Nicaraguan Seed-Finch. Try as I might, it refused to come in any closer. I kept birding up and down the road to no avail and eventually had to concede defeat. The Canebrake Wrens remained unseen, and unheard as well. But it was a nice walk and I padded my day list which was fast approaching 120. 

Olive-throated Parakeet - La Selva Biological Station, Heredia, Costa Rica

With the sky beginning to sink in the sky I reconvened with Laura and my parents at the cabin. We used the last hour of light to walk a different trail (Sendero Zompopa) which flanks the east bank of the Río Puerto Viejo. Along here, Laura came through with a sleeping Hoffman's Two-toed Sloth far off the trail.

Hoffman's Two-toed Sloth (Choloepus hoffmanni) - La Selva Biological Station, Heredia, Costa Rica

Following another hearty dinner, the four of us set off down the entrance road for a night hike. I have heard in the past that this entrance road can be excellent for mammals, especially opossums on the hydro wires. Of course it just so happened that vehicles picking up workers drove past us every five minutes along this road, severely limiting our wildlife sightings. But we still saw a few things!

Common Pauraque nest - La Selva Biological Station, Heredia, Costa Rica

Orophus sp. - La Selva Biological Station, Heredia, Costa Rica

My dad spotted this opossum alongside the road - a Southern Opossum. This is a widespread species across much of Central and South America, but it was the first that I had seen. This species has a broad capability to adapt to environmental changes and as a result they are fairly widespread in secondary forest and inhabited areas.

Southern Opossum (Didelphis marsupialis) - La Selva Biological Station, Heredia, Costa Rica

I am a big fan of Leaf Katydids! This one is a member of the genus Mimetica.


Mimetica sp. - La Selva Biological Station, Heredia, Costa Rica

Leafhoppers, treehoppers, planthoppers and froghoppers are all favourite groups of mine. These unique hoppers have an incredible diversity of shapes, colours and patterns. This is a type of froghopper called Mahanarva costaricensis, a species with a limited range in Central America. 

Mahanarva costaricensis - La Selva Biological Station, Heredia, Costa Rica

Herps were difficult to come by during our walk, no doubt a reflection of the very dry conditions. All we could turn up were a few frogs. 

Masked Treefrog (Smilisca manisorum) - La Selva Biological Station, Heredia, Costa Rica

Leaf Litter Toad (Rhaebo haematiticus) - La Selva Biological Station, Heredia, Costa Rica

My parents turned around to call it a night but Laura and I pressed on, looping back along the Sendero Zompopa. This extra hike was well worth it since I discovered an adult Blunt-headed Treesnake. Despite being a common snake in secondary growth they are one that I never grow tired off. Their ridiculous proportions are almost unfathomable. For a snake whose circumference equals that of a slim pencil, it is a wonder how long they can grow.

Blunt-headed Treesnake (Imantodes cenchoa) - La Selva Biological Station, Heredia, Costa Rica

Blunt-headed Treesnakes feed on a variety of things, though anoles and other small lizards seem to be a favourite menu item. Cruising the understory of secondary growth is a great technique for this species, since many sleeping anoles can be found in these habitats. 

Blunt-headed Treesnake (Imantodes cenchoa) - La Selva Biological Station, Heredia, Costa Rica

Laura and I checked a few more areas before calling it a night. It had been a very productive day, with 123 bird species among all the other fun finds! The following morning would be our last at La Selva before would depart for the Pacific coast. 

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