About Hyalinobatrachium fleischmanni (Boettger, 1893)
Hyalinobatrachium fleischmanni, commonly known as Fleischmann's glass frog or the Northern Glass Frog, is a small arboreal glass frog species that lives in lowland and mid-elevation forests of Central and South America. Males measure 19–28 mm in length, while females are slightly larger, ranging from 23–32 mm. They have a primarily green semi-translucent body with pale yellowish spots, yellow fingertips, and translucent skin covering the stomach. A guanine sheet covers half of the frog's underbelly, stretching over several internal organs but leaving parts like the liver visible. Their hands are yellow and translucent, and skin spots match the color of local leaves. Unlike tree frogs, which they closely resemble to the naked eye, H. fleischmanni have forward-pointing golden eyes. Their green skin reflects visible light between 400 nm and 700 nm. Males have a visible white vocal sac used for mating calls, and a noticeable hook protruding from their spine, which is thought to be used for fighting other frogs or defending territory or eggs; females are larger and do not have this spine hook. When approached or threatened, these frogs freeze and do not move. They are nocturnal carnivores, active on rainy nights to keep their skin moist, and feed on small insects including crickets, moths, and flies, as well as spiders and even other smaller frogs. During the day, they camouflage themselves under leaves above water. Strong rainstorms can kill these frogs, as a direct impact from a single raindrop has been observed to be fatal. Fleischmann's glass frogs inhabit areas near fast-moving streams, in forests up to 2,000 meters above sea level, with a broad geographic range extending from Mexico to Ecuador and Suriname. It is one of the most altitudinally diverse species in its genus, found from approximately sea level to above 1,600 m. In Costa Rica, it occurs in lowland wet forests, rainforests, and higher elevations; it avoids dry areas such as the northwestern lowlands, high mountains, and coasts, and is the most abundant glass frog species in the country. Over 100 glass frog species have been recorded across Central and South America, with 13 of these found in Costa Rica. As arboreal frogs, they live in trees. Males typically do not hold the same territory for long. Most males remain in a single territory for around ten days, with an overall range of 1 to 18 days; some stay for 15 to 20 days or longer. New territories are usually within two meters of the original territory, though they can occasionally be as far as five meters away. A single territory can hold up to five egg clusters. Males occupying large leaves usually stay on the same leaf after laying eggs to attract additional females, while males on small leaves typically move to another leaf on the same plant. Male calling sites are most often found on the undersides of leaves of broad-leaved plants such as Dieffenbachia, as well as on shrubs, ground bromeliads, and epiphytes on tree trunks, 0.5 to 10 meters above ground. Males prefer calling sites positioned over the main stream channel, so calling sites are typically 0 to 6 meters from the water. Calling activity occurs during the rainy season. Males begin calling at dusk, and calling often continues until dawn, decreasing in frequency as the night progresses. Males do not call when they are engaging in amplexus or guarding eggs. While conspicuous calling helps males attract females, it also increases their risk of being detected by predators. The breeding season for H. fleischmanni runs from May to September, when females regularly seek out mates. When a female approaches a calling male in vegetation, she stops moving near him, pushes him gently from the side, crawls under him, and the male clasps the female in amplexus. Females prefer to lay eggs on overhanging leaves above rivers, laying clutches of 18 to 30 eggs on the undersides of leaves or lower branches near flowing water. Clutch size varies depending on the time of year. Around 80% of all clutches are eaten or destroyed by threats including fungal infections and predators such as crickets and possums. After laying, the male stands guard over the clutch to protect eggs from predators until hatching. Male guarding behaviors include staying with the clutch and urinating on eggs to prevent them from drying out. Eggs hatch between 8 to 21 days after laying, most often after 10–15 days. All tadpoles in a single clutch hatch within one day, and leave the clutch within 2–3 days. When they hatch, tadpoles drop into the stream below, where they hide in silt and debris at the river bottom. Tadpoles go through a series of color changes as they develop: they start yellow, turn orange, then turn red. Hatching almost only happens when tadpoles reach the orange or red stage; yellow tadpoles generally cannot survive on their own, so their early disappearance is most often due to predation. Tadpoles are able to survive independently once they reach the orange stage by the eighth or ninth day of development. Tadpole maturation is slow, taking between 1–2 years to complete.
