Coquí

The common coquí is native only to Puerto Rico, where it is the most widespread of about 17 native frogs of the same genus, many of them also called coquís. It lives in an impressive range of places, from the canopy of El Yunque rainforest to coastal scrub, mountain slopes, backyard gardens and city parks, and from sea level up to the high forests of the Cordillera Central. By day it hides in bromeliads, leaf litter, tree bark and under broad leaves, and it comes out after sunset. Bromeliads are especially important, because the water and damp debris they hold give the frog a cool place to wait out the day. Outside Puerto Rico, the coquí has been carried to other places in shipments of plants. It is established in Hawaii and the US Virgin Islands, it has been reported in the Dominican Republic, a small population has lived in Turrialba, Costa Rica, since about 1998, and it has turned up in a few plant nurseries in Southern California.

The coquí is small enough to sit on a person's thumb. Adult males usually measure 3 to 3.7 centimeters from snout to vent and females 3.6 to 5.2, so females are clearly larger, and an adult weighs only a few grams. The skin color varies a lot among individuals, from pale tan and warm brown to olive and soft green, often with darker streaks or spots along the back that help the frog blend into leaves and bark. Many carry a pale stripe or a pair of light marks between the eyes, and some have a pale band across the back or a light stripe down each side. The belly is paler. For a frog that spends its life climbing plants, the most useful features are the enlarged toe pads, which grip smooth or wet surfaces. Unlike most tree frogs, it has no webbing between its toes. The eyes are large for the size of the head and give the coquí good vision in dim light as it hunts through the night.

Few sounds are as tied to a place as the call of the coquí is to Puerto Rico. Only the males sing, and they do so almost every night of the year, starting shortly after dark and often continuing until dawn. The call has two distinct notes. The first, a low "co", is a territorial warning to other males. The second, a bright, rising "kee", attracts females. Females hear the two notes differently from males, so each part of the call reaches the right listener. Researchers have also found that the pitch changes with elevation: frogs in the mountains are larger and call lower than those near the coast. When many males call together, the chorus can pass 90 decibels close to the frogs, about the level of heavy traffic. Puerto Ricans living abroad often say they miss this sound, and recordings of the coquí are used to evoke the island in music and film.

Most frogs lay their eggs in water and go through a tadpole stage, but the coquí does neither. After a male attracts a female with his call, she lays a clutch of about 16 to 41 eggs, usually close to 30, in a sheltered spot on land, such as a curled leaf, a bromeliad or a palm frond. The male then takes over. He sits on the eggs to keep them moist and protects them from predators, including other coquís that would eat them, and he stays with the clutch day and night. Inside each egg the embryo develops straight into a tiny frog, with a tail that is used for breathing and then absorbed before hatching. After about 17 to 26 days, froglets only a few millimeters long break out of the eggs, and the male may stay with them for several more days. A female can lay several clutches a year, about eight weeks apart. Because it needs no ponds, the coquí can breed far from water, which helps explain how it spread so easily in Hawaii.

The coquí is a predator and a prey at the same time. At night it hunts a wide range of small invertebrates, including ants, beetles, moths, flies, crickets and spiders, sitting still on a leaf and snapping up whatever passes within reach. Young frogs take tiny prey such as mites and springtails, and larger adults can eat bigger insects and even small snails. Because coquís live packed so closely together, studies in the forests of eastern Puerto Rico estimated that they eat more than a hundred thousand invertebrates per hectare every night. That makes them an important control on insect numbers, and their droppings return nutrients to the forest floor. As prey, coquís feed snakes, lizards, birds, tarantulas and larger frogs. Because they are so abundant and widespread, they move a large amount of energy through the food web, and after hurricanes damage the forest, the number of coquís rises and falls with the amount of shelter left on the ground.

The coquí reached Hawaii in the late 1980s, hidden in potted plants, and it landed on islands with no native frogs and few animals that hunt them. Densities there have been measured at up to about 91,000 frogs per hectare, far beyond what the species reaches at home. The chorus that Puerto Ricans remember with affection is treated in Hawaii as noise pollution, and in some neighborhoods it has been linked to lower property values. State agencies spray a citric acid solution on infested vegetation, nurseries are inspected before plants move between islands and residents are asked to report new calls. On the Big Island the frog is now too widespread to remove, while smaller populations on Oahu and Kauai have been largely controlled. The frogs also change the forest, eating huge numbers of leaf litter invertebrates and altering how nutrients cycle. It is the same animal singing the same song, valued at home and fought against far from it.

For generations, the coquí has meant far more to Puerto Ricans than a frog that sings at night. It is one of the best known symbols of Puerto Rican identity, appearing on handicrafts, murals, jewelry, clothing and public art across the island and in Puerto Rican communities in the United States. The saying "de aquí como el coquí", from here like the coquí, is used to claim the island as home. Children grow up with songs and stories about the frog, and its image is used in schools to teach pride in local nature. A widely shared belief says that coquís taken off the island stop singing, a story about the bond between the frog and its homeland. The frogs of Hawaii, which sing loudly every night, show that it is not literally true, but the saying still captures how closely the coquí is tied to Puerto Rico. Not all coquís are doing as well as the common one, and several of its relatives on the island are now threatened.