Costa Rican seasonal moist forests

A mile-a-minute vine (Ipomoea cairica) was confirmed at research grade along the forest edge near Puntarenas on August 17. That single record turns out to be one thread in a larger picture: over the past 30 days, eight separate introduced ornamental species have been logged around this stretch of Costa Rican seasonal moist forest, among them thatch screwpine, golden pothos, crepe ginger, blue pea, lesser bougainvillea, red ginger, and sea almond. These are opportunistic community-science sightings over a single window, so they can't establish a trend on their own, but the number and variety of introduced ornamentals turning up together is worth noting. Mile-a-minute vine earns its common name honestly. It is a fast-growing perennial liana that climbs rather than roots deep, and that habit is exactly what makes a forest edge vulnerable: the edge is already sunlit and disturbed, thick with low shrubs and saplings for the vine to scramble up. It throws itself over that structure and shades out the leaves beneath before they can respond, and once it reaches the canopy gap light an edge provides, it holds that light for itself. Ornamental escapes do not need a storm or a flood to reach a forest edge, only a nearby garden and a bird or a drainage line to carry the seed the rest of the way. Puntarenas's settlement edges sit directly against this forest, and eight escaped ornamentals surfacing in a single month is worth watching as a possible sign of spillover from garden to forest edge, even if a single month's sightings can't confirm it.

The roads and trails around Sámara and along the Ruta del Sol have turned orange and black this week with an unusually large pulse of Halloween Crabs (Hartnollius quadratus), a native land crab of this stretch of the Nicoya coast. Community sightings jumped from a handful a month for most of the year to roughly eighty in the first five days of August alone. The same week last year produced a single record. The records themselves sketch the shape of it. Reports come both from the coast — Sámara, Playa Ostional, Puerto Carrillo — and from inland stretches of Ruta del Sol through Nicoya and Hojancha, and they pile up almost entirely within a few days at the start of the month, in the middle of the wet season. One observer note filed with these records describes the species as a burrower of tropical forest, mangrove and humid coastal ground, which fits a crab that spends most of its life out of sight and then, briefly, is impossible to miss. Why they all move at once is the obvious next question, and it is the part we can't answer from this data. Coastal land crabs of this kind are widely reported to make seasonal migrations to the sea to breed, and a tight, rain-season pulse spread between forest and beach is consistent with that — but nothing in the observation record confirms the mechanism, the cue, or which animals are on the move. Treat the migration story as the likely explanation rather than a documented one. The count comes from sightings logged by observers rather than a headcount of crabs on the ground, and most of the early-August records are still awaiting community confirmation of the identification, so this reads more accurately as a strong pulse than a precisely measured boom. Either way it is one of the more visible seasonal events in this corner of the Costa Rican seasonal moist forests, and it marks this as a good year to watch the roadside verges after dark.

The forest-interior lepidoptera community has shifted entirely with the rains. The sun-loving sulphurs, swallowtails, and queens that dominated the dry months have withdrawn, replaced now by owl-butterflies moving through the shaded understory since late June, daggerwings working the forest edges into early July, and — most tellingly — an Anchemola Sphinx (Eumorpha anchemolus) logged on July 15. These large hawk moths vanish during the dry season and return with the rains to work the night flowers. Their arrival marks one of the forest's clearest seasonal pulses. Sphinx moths carry an outsized ecological role here. With tongues longer than their bodies, they are the primary pollinators of deep-tubed flowers that no hummingbird or other insect can reach — making their return as essential to the forest's reproductive cycle as the rains themselves. Over six months of observation, four sphinx moth species appeared during the dry months, but only the Anchemola Sphinx during the wet season's peak. Their presence, alongside the shift to shade-dependent butterflies, is a quiet affirmation that the forest corridor remains connected enough to support the full community of specialists, not merely the generalists that persist in fragments.

American Crocodile (Crocodylus acutus) appeared in the estuary this week as tides ran 17 centimeters above prediction, pushing the brackish zone farther inland — the kind of tidal anomaly that pulls these reptiles from deeper channels into the wider, wetter margins they depend on. Hunted nearly to extinction in this region during the last century, they have rebuilt slowly across decades. Two research-grade sightings in the past six months suggest the population is still recovering, but each swollen July estuary offers temporary habitat that may allow them to venture upstream into areas that were empty for generations.

Yellow toads (Incilius luetkenii) are calling in chorus as the rains settle in — the most abundant amphibian sightings recorded here over the past three months. These small toads breed in synchronized pulses timed to the wet season's onset, their voices rising with the first consistent downpours. On the Nicoya Peninsula, farming families have long read these calls as a planting signal, timing their crops to the toad's rhythm. That folk knowledge rests on close observation of a real ecological connection: the toads' breeding chorus marks the point when soil moisture and insect abundance align for successful reproduction. The rains are holding, and so are the toads — both signals in sync, as they have been for generations.

The beach near Nandayure goes quiet as the light drops. The dry season birds have pulled back into the forest edge, and the surf takes over the soundscape. This is the hour the hawksbill turtles come ashore. Hawksbills are smaller than the leatherbacks or greens that share these Pacific waters. An adult female weighs around eighty kilograms, and her shell is narrow and tapered at the front, with overlapping scutes that give it a ridged, shingled look. Her beak is pointed and slightly hooked, shaped for pulling sponges off coral heads. She spends most of her life at sea, feeding in the reef systems offshore, but summer draws her back to this stretch of sand. She navigates by the earth's magnetic field, detecting both the intensity and inclination of the field lines, and she returns to the same beach where she hatched. Not the general region. This beach. Researchers have documented females nesting within meters of where they emerged decades earlier. She comes ashore after dark. She moves across the wet sand slowly, pulling herself with her front flippers, pausing to rest. Above the tide line she begins to dig. First a wide body pit, scooped out with all four flippers. Then, from the back of that pit, the egg chamber: a flask-shaped cavity about forty centimeters deep, excavated with her rear flippers working in alternating scoops, one at a time, each one curling and pressing the sand out to the side. The chamber takes twenty minutes to an hour to dig, depending on the sand. When it is finished she lays between one hundred and two hundred eggs, each one soft-shelled and slightly smaller than a golf ball. She covers the chamber, filling it and tamping the surface, then sweeps sand across a wider area to obscure the site. By the time she returns to the water the work is done. The eggs incubate in the sand for about sixty days. The temperature inside the chamber matters: cooler incubation produces more males, warmer produces more females. The nest is not tended. The female may return to this beach three or four more times this season, laying another clutch every two weeks or so, but she does not come back to the eggs she has already buried. When the hatchlings emerge they dig up through the sand together, usually at night, and orient toward the ocean by moving toward the brightest horizon. On a dark beach with no artificial light, that is the sea. Light from buildings or roads pulls them in the wrong direction, and many do not make it to the water. Hawksbills are critically endangered. Their populations have dropped sharply over the past century from hunting, egg collection, and the destruction of the coral reefs where they feed. The sea almond trees you may notice at the upper edge of the beach are an introduced species, non-native to this coast, and their spread can alter the slope and shade of the upper beach in ways that affect nest temperatures. The pressures on this animal are real and have accumulated over a long time. But the turtles are still here. On beaches like this one, nesting females still come ashore in summer, still dig their chambers by feel in the dark, still return to the same sand they came from. If you are near the water's edge as the last light fades, look at the wet sand above the wave line. A hawksbill track is distinctive: the front flippers leave marks on both sides simultaneously, like two hands pressing down together, with a tail drag down the center. The track goes up the beach and, if she has finished nesting, comes back down again. The sand where she turned around will be disturbed and smoothed, the surface worked over. Look for that, and then look at the water. Somewhere out there, beyond the surf, she is already gone.

Great Curassows are nesting in Guanacaste's dry forest now, seen daily through June 20. Hunted and forest-lost across Central America, this large ground bird holds on mainly in protected corridors like this one. Their presence into the wet season is a quiet sign the habitat is intact.