Poison Frogs: Dendrobatidae
Behavior And Reproduction
Almost all of the poison frogs are active during the daytime, usually at dawn and late in the afternoon, and especially when it rains. The most toxic species hop about in plain view of potential predators, but the predators normally leave them alone to avoid a dangerous mouthful of poison. The frogs that do not have dangerous toxins in their skin are typically dull-colored and blend in with their surroundings. This camouflage usually keeps them out of their predators' sights. If a predator does spot a frog, the poison frogs have strong legs to help them leap away. Some of the frogs also are very good climbers and can avoid ground-living predators by scrambling up bushes and trees. The family name, Dendrobatidae, actually comes from two words that mean tree and walker in Greek. The Brazilian poison frogs and the polka dot poison frogs are two species that spend their lives in the trees.
The Venezuelan skunk frog is unusual, in part, because it is active at night. This species has an odd but effective defense against predators. As its common name suggests, it has a very strong, skunklike odor that wards off attackers. Scientists are interested in this species, which was discovered in the 1980s, because it may help them figure out which other families of frogs are most closely related to the poison frogs. Although scientists are not sure, they think the poison frogs' nearest relatives may be the true toads in the family Bufonidae, or the leptodactylid frogs.
The males of many species set up and defend territories against other males. These territories can be important during the mating season. Studies of strawberry poison frogs, for example, have shown that the males with the best territories are the best at attracting females. In this case, the best territories are those that are larger and have more tall places where the males can call to females. Often, male poison frogs defend their territories with a certain type of call, called an encounter call, that tells other males to stay away. In some species, like Stephen's rocket frog, the encounter call is different from the call that they use to attract females. In other poison frogs, the two calls sound much alike and may even be the same. The Trinidad poison frog is different because the females instead of the males are the ones who set up and defend territories. The females cannot call, so they defend their territories by rippling their bright yellow throats while sitting up tall in a high spot of the territory. In the green poison frog, the female does not set up territories, but she will fight with other females that approach her mate.
The breeding time for poison frogs is commonly during the rainy season, which runs from about November to April, although it may be a bit longer or shorter in some areas. Males call the most early in the day; then they quiet down. If the day is rainy, however, they may start calling again later in the afternoon. Some species, like Stephen's rocket frog, may call any time of day if it is raining. The males call from land. Some call from the leaf-covered ground, others from a hole in a tree trunk, and some species from plants that grow on the sides of trees.
For many species, scientists have never seen the males and females mate. In others, like the harlequin poison frogs, they have a good deal of detail. In this species, the male calls to attract a female. When she comes toward him, he continues calling while hopping away and leading her to the mating site, which is under leaves on the forest floor. This species is one of many, including the green poison frog, the blue-bellied poison frog, and the strawberry poison frog, that lay their eggs in leaves lying on the ground. The female blue-toed rocket frog places her eggs inside rolled or folded leaves. Other species of poison frogs lay their eggs in the trees. The female Brazilian poison frog, for instance, lays her eggs in small, wet tree holes just above a water puddle inside the hole. All of the poison frogs lay their eggs out of the water, except possibly the Venezuelan skunk frog. No one has seen where this water-loving frog lays its eggs. The female may lay them in the water, or she may come out to lay the eggs on land.
Some of the poison frogs have only a few eggs at a time. The female blue-bellied poison frog usually lays just two eggs, the female Brazilian poison frog lays two or three, and the strawberry poison frog lays two to six in a clutch. Many additional species also have small clutches. Other frogs in this family, including the blue-toed rocket and phantasmal poison frog, have larger clutches. The female blue-toed rocket usually lays about nineteen eggs, while the female phantasmal poison frog lays between fifteen and forty eggs in a single clutch.
In most other types of frogs, both adults leave after the eggs are laid. In poison frogs, however, either the male or the female stays behind with the young until they hatch into tadpoles. Occasionally, both adults stay with the eggs. In the green poison frog, for example, the male continues to check on the eggs during the two weeks it takes them to hatch. During this time, he turns the eggs, adds water to them to keep them moist, and removes any fungus that may have started to grow on them. The male is also the caregiver in the blue-bellied poison frogs, the Amazonian poison frogs, the phantasmal poison frogs, the Trinidad poison frogs, and others. The harlequin poison frog is one of several species in which the female stays with the eggs. In a few species, including the strawberry poison frog and the Brazilian poison frog, the adults share the job.
Part of the care includes carrying the tadpoles to water where they will continue to grow and develop into froglets. In most cases, the adult sits in the middle of the hatching eggs, and the tadpoles squirm onto the adult's back. The adult then moves over to water, sometimes spending quite some time searching for the perfect spot, and drops off the tadpoles. In some species, the adult carries only one tadpole at a time and has to make a few trips from the nest to the water before he or she has moved the entire family. Once the adult has delivered all of the tadpoles to the water, the tadpoles are on their own. Among green poison frogs, one male may mate with and have young by more than one female during one breeding season. Since he is the caregiver for the eggs, he has to watch over several nests at once. Sometimes, he is not successful, and some of the tadpoles die before he can get all of the young to water.
In the strawberry poison frog, the male cares for the eggs by keeping them moist and clean, but the female takes over when the eggs are ready to hatch. She carries one tadpole at a time to plants that have puddles of water laying at the base of their leaves or filling a cup that forms from their overlapping leaves. These small puddles do not contain much, if anything, for the tadpoles to eat, so the female comes back to her growing young every five days or so to feed them. The food she leaves is additional eggs that she lays. The eggs are infertile (in-FER-tul), which means that they will never develop into young. The tadpoles eat the infertile eggs until they grow and mature into froglets.
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