Birdsong, Logged: The BirdWeather Station at Mar-a-Selva

At three in the morning the hillside above Playa Ocotal is not quiet. It is only unlistened to.

There is a small weatherproof box in the trees at Mar-a-Selva that does the listening on our behalf. It has been running since 17 June 2025. In that time it has heard 158 species and written down 91,623 individual calls, and it has not slept once.

Birdwatching in Costa Rica usually means a guide, a five a.m. alarm and a long drive. Here it also means this: you can see what the hillside is saying right now, from wherever you are reading this, before you have booked a single night.

What the box is

A BirdWeather PUC — two microphones, a GPS and a stack of environmental sensors, running a neural network that recognises more than 6,400 species by sound in real time. The model is BirdNET, a research collaboration between the Cornell Lab of Ornithology and Chemnitz University of Technology. There are over two thousand of these stations worldwide. Ours is number 15022, and every detection it makes is public. No account, no subscription.

The day is split between two voices

The most striking thing in fifteen months of data is how evenly the twenty-four hours are divided, and by whom.

The Great Kiskadee owns the daylight: 28,538 detections. It says its own name, repeatedly, from an exposed branch, at volume, and it starts before you would like it to.

The Pacific Screech-Owl owns the dark: 28,181. Within a rounding error of the kiskadee. Most guests never see one. Everybody hears them.

Two birds, almost exactly half the record each, handing the hillside back and forth at dawn and dusk. That is the soundtrack of the house, quantified.

Third place, and the bird you will actually meet, is the White-throated Magpie-Jay — big, blue and white, absurdly crested, and loud. They travel in gangs and scold whatever they dislike. They are omnivores with poor manners: insects, nectar, fruit, and the nestlings of other birds. They will raid a papaya the day before you meant to pick it. After that the dry-forest cast fills in: Common Pauraque calling from the road at dusk, Rufous-naped and Banded Wrens, Tropical Kingbird, Boat-billed Flycatcher, White-fronted Parrots going over in pairs, Squirrel Cuckoo, Lesser Ground-Cuckoo, Collared Forest-Falcon.

Right now, the list is changing

Autumn does something to the register. A Belted Kingfisher has been working the shoreline this week — the station has logged that species 56 times in its whole history, and 21 of those were in the last seven days. Ospreys are back over the water. A Broad-winged Hawk came through at midday. Somewhere out there is a Ruby-throated Hummingbird that weighs as much as a penny and has just arrived from a feeder in North America.

We wrote about that separately: which northern birds are arriving at Mar-a-Selva right now.

The one everyone wants to see

The Turquoise-browed Motmot, and the station picks it up regularly.

Green and blue and black with an orange breast, and two long central tail feathers stripped bare except for racquet-shaped tips. Both sexes swing that tail slowly side to side — in males during breeding it is courtship; otherwise it appears to be a signal to a predator that it has been seen. They nest in burrows they dig into ravine banks, tunnels a few inches wide and up to eight feet deep. They are mostly a Guanacaste bird, they perch conspicuously on wires and fence posts, and they are famously unbothered by people. The local name is pájaro bobo — roughly, the foolish bird — for exactly that reason.

One correction worth making, because it is repeated constantly: the motmot is not Costa Rica’s national bird. It is the national bird of El Salvador and Nicaragua. Costa Rica’s is the Clay-colored Thrush — the yigüirro — a plain brown bird whose song is said to call in the rains.

Also on the list and worth watching for: Black-headed Trogon, Elegant Trogon, Orange-fronted Parakeet, Hoffmann’s Woodpecker, and, occasionally, a Streak-backed Oriole.

What the machine gets wrong

We are going to be straight about this, because it is more interesting than pretending otherwise.

The species list is not a clean checklist. Sitting on it are a handful of birds with no business on a Guanacaste hillside — a House Sparrow, an Acorn Woodpecker, a Montezuma Oropendola. Those are almost certainly misfires: a sound that resembled something else, a confident model making a call it should not have. Every detection carries a confidence score, and reading them critically is half the fun.

Meanwhile some real birds of this forest have never turned up at all. The Long-tailed Manakin — saltarín toledo, named for its to-lay-do call, where two or three males perform a cooperative dance for a single female — lives in Guanacaste forest, and our box has not caught one. Nor has it logged a Ferruginous Pygmy-Owl, which is a shame, because it is the bird every songbird in the neighbourhood hates: one study recorded up to forty birds of eleven species mobbing a single owl.

Absence in the data is not absence from the hill. It only means nothing called within range of two microphones.

The thing that isn’t a bird

You will hear mantled howler monkeys before you are properly awake, and you will think something large is coming for the house. It is a leaf-eating monkey the size of a raccoon whose call carries more than a kilometre.

There is a reason for the volume. Howlers live on leaves, which is a poor diet to fund a fight — so they settle territorial disputes by shouting across the valley rather than crossing it. The noise is the entire strategy.

Why the hillside and not the beach

Mar-a-Selva sits up in the trees above Playa Ocotal, and that elevation is the whole reason the station has anything to report. The beachfront is open and built on. Up here it is dry forest — thick in green season, bare and bright in March, and full of things that call.

Bring binoculars. The best hours are the first two after dawn and the last one before sunset, which falls somewhere around 5:20 to 5:45 depending on the month.

And before you come, go and look at what the box is hearing today. It is the most honest preview of a place we know how to give you.

Open the Mar-a-Selva station · Check available dates

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