Northwestern Yucatan Plain with Low Tropical Deciduous Forest

Something is walking across the roads and yards on the north side of Mérida this August, and it has eight legs, a dense coat of bristles, and a rust-colored patch on its abdomen that gives it its name. The Yucatán Rust-rump Tarantula (Tliltocatl epicureanus) appears to be turning up in greater numbers than usual, with 30 sightings logged on iNaturalist this May-through-August window compared to 10 over the same stretch in 2025. Eight of those records came in the last two weeks alone, clustered in a band running from the city's edge out toward the coast.This spider is a Yucatán Peninsula endemic, found nowhere else on Earth, which makes any shift in its visibility here worth paying attention to. Like other mygalomorph tarantulas, the males spend most of their lives in a single burrow, ambushing insects and the occasional small vertebrate that wanders too close to the entrance. They only leave that burrow behind once they mature, and when they do, it is for one purpose: to wander in search of a female's silk-lined tunnel during the rainy season. A male that has left home for good, with no burrow of his own left to retreat to, is a male with nothing to do but keep moving, which is exactly what puts him in a driveway or crossing a road in broad view of a person with a phone.That life-history detail makes mating dispersal a plausible explanation for this year's higher count, though a growing number of people logging sightings on the app over the same period could also be inflating the numbers, and the underlying counts are still small enough that some of the swing could be noise. The pattern to watch for is whether these sightings taper off as the rains ease later in the season; that decline would be consistent with the ordinary, if dramatic, business of a mature male tarantula looking for a mate, rather than anything unusual happening to the species itself.

A small wetland tucked into the San Antonio Kaua II neighborhood of Mérida, known locally as Acuaparque, has quietly become reliable habitat for Snail Kites. Over the past year, birders have logged the species there nearly every month, from August 2025 through a sighting just three days ago, and nearly all of those records cluster at this one constructed or semi-natural water feature rather than scattering across the wider region.The kite is a specialist in the truest sense of the word. Its bill is thin, sharply hooked, and curved almost like a can opener, and that shape exists for a single task: reaching into the shell of an apple snail and lifting the animal free without breaking it apart. Snail Kites eat almost nothing else, which makes an individual bird a living instrument for reading the marsh beneath it. A kite has no reason to linger anywhere the snails aren't, so repeated sightings at one small pond are really a report on that pond's water chemistry, its vegetation, and its snail population, month after month.Finding that signal at one modest urban water feature, surrounded by streets and rooftops rather than open wetland, says something about how much ecological value a small, well-maintained patch of marsh habitat can carry when the water level and prey base hold steady. It doesn't take a large wetland to matter; it takes the right shallow water with snails in it.The Snail Kite is flagged as threatened in this region, which raises the stakes on a site like this. Birds at this latitude are typically assigned to the local subspecies, Rostrhamus sociabilis major, though the threatened designation in the records comes at the species level rather than from a subspecies-specific assessment. The record here also comes from community birding sightings rather than a formal survey, so that kind of data can't confirm breeding or year-round residency. But a full year of recurring sightings at one named site, rather than a scattered handful of one-off records, is the kind of pattern that deserves continued watching rather than a shrug of coincidence.

Black Spiny-tailed Iguanas (Ctenosaura similis) are in full breeding season across Mérida's margins — six confirmed sightings in the past ten days, from a supermarket parking lot in Kanasín to a neighborhood park on the city's north side. July is when females excavate nesting burrows in loose soil and males claim stone-wall territories in what fragments remain of the tropical forest that once blanketed this plain. Now, their habitat is mostly old colonial stonework, rubble lots, and scattered large trees that have survived the city's expansion.Moving through the same walls and gardens alongside the iguanas are three invasive competitors: Brown Anoles from Cuba, Brahminy Blindsnakes from South Asia, and Asian House Geckos — all now colonizing the same margins where iguanas must breed. Known in Yucatec Maya as the tolok, this iguana has been eaten, traded, and tended in Maya communities for centuries. Whether it can nest successfully in a city expanding as fast as Mérida is — surrounded by a growing roster of introduced species — remains one of the quiet ecological questions of this wet season.

Water levels have run 30 centimeters above predicted tides for the past two weeks along this flat karst coast — a sustained surge that is now pushing well up into the nesting beaches at the height of the breeding season. Hawksbill and Green Sea Turtles both deposit eggs well above the normal wash line — an adaptation to protect clutches from regular tidal cycles. When water levels hold 30 centimeters above predicted heights for weeks at a time, those eggs are flooded, and sustained inundation starves them of the oxygen they need to develop.This coast lacks a ridge or other topographic buffer to shelter the upper beach. The eggs laid here over recent months are now directly exposed to conditions they evolved to avoid.

Tidal water stands 30 cm above predicted today on this flat karst coast — a surge that pushes saltwater well inland into freshwater wetland edges. On the Yucatán shelf, there is almost no topographic buffer: even small departures from normal tide become ecological boundary crossings. This matters acutely because Furrowed Wood Turtles (Rhinoclemmys areolata) nest along these same edges this season, and saltwater intrusion into their nesting habitat is a direct threat to eggs and hatchlings.As hurricane season opens, the water is already sending a signal. These pulses are becoming more frequent and more severe. For now, turtles nest where they have nested for generations — but the margin between freshwater wetland and salt is narrower than it once was.

Snail Kites have made over 40 visits to a single urban pond in Mérida during the first five months of this year, a striking testament to how raptors adapt when their natural habitat vanishes. This threatened species depends almost entirely on apple snails, and what was once dispersed across vast wetlands now concentrates on whatever shallow ponds persist in the city's margins.Common water hyacinth appeared at the site in late June—a sign of trouble. These floating plants mat over open water, eliminating the shallow habitat snails need to thrive. For a raptor species that has already lost most of its range to agricultural conversion and wetland drainage, the presence of invasive vegetation in one of its last urban refuges is a reminder that survival in fragmented landscapes is perpetually precarious.

After dark in Mérida, when the heat of the day finally softens and the air thickens with humidity, the city's trees become something else entirely. The rains have arrived. Standing water collects in tree hollows, in bromeliads, in the gaps between roots. This is what the milk frog has been waiting for.Milk frogs are large, pale, and built for the canopy. An adult is broad-headed and heavy-bodied, with adhesive toe pads that let it move across bark and leaf surfaces with ease. The skin is smooth and whitish, sometimes faintly mottled, and the eyes are large and gold-rimmed. During the dry months they are quiet and largely invisible, sheltering in tree cavities and waiting. But when the summer rains saturate the Yucatan Peninsula and water gathers in elevated pools, the frogs descend from their retreats and begin to call. The sound is loud and repetitive, a low resonant honk that carries well through dense vegetation. A calling male stations himself near a water-filled hollow and calls through the night, sometimes for hours. Other males respond. The result, on a good rainy night, is a layered chorus that bounces off walls and canopy alike.The vocalization does two things at once. It draws females, who select mates based on call quality and persistence, and it signals other males about occupied space. Males that approach too closely trigger escalating call exchanges, sometimes followed by physical contact. Females move through this acoustic field and eventually approach a male at the water source. Eggs are laid directly onto the surface of the water pooled in the hollow, and the male fertilizes them there. The hollow matters: it protects the eggs from the kind of predation that ground-level clutches face, and the enclosed space keeps humidity high around the developing embryos. Tadpoles hatch and develop in the same water column, feeding on algae and organic debris that accumulates in the hollow. In a tree cavity with enough volume and shade, a clutch can develop through to metamorphosis in a few weeks.The milk frog's reliance on arboreal water means it is sensitive to the availability of large, mature trees. Old-growth trees develop the deep cavities and structural irregularities that hold standing water; younger, smoother trees rarely do. In and around Mérida, that means the frog is concentrated in older parks, established neighborhoods with large shade trees, and patches of remnant forest. It shares some of this space with the invasive greenhouse frog, a small direct-developing species that needs no standing water at all and breeds in moist soil and leaf litter. The two frogs occupy different microhabitats and don't compete directly, but the greenhouse frog's presence is a measure of how modified the surrounding landscape is. Where greenhouse frogs are common, the original structure of the habitat has changed.The ferruginous pygmy-owl hunts at dusk and dawn in the same trees where milk frogs call at night, and a large frog on an exposed branch is within range of what that owl will take. The northern potoo, which roosts motionless against bark during the day, is active in the same hours as the frogs. Whether potoos take milk frogs directly isn't certain, but they occupy the same nocturnal canopy and hunt by sight in low light. The gray fox moves through the understory below and would take a frog that descended to the ground.The milk frog's skin produces a thick, whitish secretion when the animal is stressed, which is where the common name comes from. The secretion is irritating to mucous membranes and likely discourages some predators, though it doesn't deter all of them. It's not venom in the strict sense; it's more of a deterrent, something a predator learns to avoid after an unpleasant encounter.If you are outside tonight, or near an open window, listen past the ambient noise for something low and repetitive coming from the trees. Not an insect. Not a bird. A deliberate, carrying call from something sitting still in the dark. The rain will have brought them out. The sound, if it reaches you, is coming from a hollow somewhere above.

The wetlands around Mérida shimmer in the late morning heat, shallow pools scattered between stands of cattail and sedge. Water levels have risen with the summer rains, flooding the margins where apple snails cluster on submerged stems. If you are walking near water today, listen for the splash of a large bird dropping to the surface.A snail kite hangs motionless above the marsh, slate-gray wings spread wide against the white sky. This threatened raptor has shaped its entire existence around one prey: the apple snail. The kite's bill curves into a sharp hook, designed precisely to extract snails from their shells. Its talons grip differently than other raptors, holding the rounded shell steady while the specialized bill works. When the kite spots movement below, it drops with controlled precision, feet first into the water.Apple snails surface to breathe through a tube-like siphon, making them visible to hunting kites. During summer, these large freshwater snails reproduce rapidly in the warm, oxygen-rich shallows. The snails scrape algae from plant stems and filter particles from the water column, converting plant matter into protein that feeds not only snail kites but also limpkins, which probe the mud with their long bills for the same prey. The kites follow water levels closely. When summer rains flood new areas, snail populations expand, and the kites adjust their hunting territories accordingly. A single kite may cover several square kilometers, moving between productive pools as conditions change.The kite that just landed carries its catch to a nearby perch, often a dead snag or the top of a palm. Here it performs the delicate work of extraction, using its bill tip to sever the muscle that holds the snail in its shell. The empty shells accumulate below favored perches, white spirals scattered on the ground like discarded pottery. Young kites must learn this technique through practice. Parents bring whole snails to the nest, and juveniles spend weeks mastering the precise movements needed to access their only food source. This specialization makes snail kites vulnerable to habitat changes, but it also makes them supremely efficient hunters when conditions are right.The water stills after the kite's departure, rings spreading outward from where it touched down. Somewhere in the shallows, another snail extends its siphon toward the surface, and overhead, another kite begins its patient circle through the humid air.