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The blue-sided treefrog, Agalychnis annae, is a leaf-green canopy frog named for the flash of violet-blue it shows along its flanks and inner legs whenever it shifts position. It is endemic to Costa Rica’s Central Valley region, found on the Cordillera de Talamanca, Cordillera de Tilarán and Cordillera Central, with a total estimated range of roughly 16,000 km2, and a possible further subpopulation in the Cerro Colorado range of western Panama.
Identification
The species is sexually dimorphic in size: adult males average about 63 mm in snout-vent length and adult females about 78 mm, while juveniles average 29 mm. Like its Agalychnis relatives, it has large golden eyes, smooth green skin on the back, and bars of blue along the sides and limbs that are hidden when the legs are folded and revealed in flight or on landing. The combination of golden eyes with blue (rather than red) eye colour and blue flank markings separates it from its red-eyed cousin A. callidryas.
Habitat and range
A. annae lives in tropical premontane and cloud forest at altitudes of about 600–1,650 m, staying close to the ponds it needs for breeding. Much of its original forest has been cleared, and the species now survives in subpopulations separated by coffee plantations, cultivated land and urban areas across the Central Valley, a fragmentation that leaves isolated groups of frogs more exposed to local habitat loss and disease.
Behaviour and breeding
As with other leaf frogs in its genus, A. annae is nocturnal and arboreal, spending the day resting on leaves in the forest canopy and becoming active after dark to feed and breed. Breeding is tied to still water: adults gather at forest ponds within their cloud-forest range to mate and lay eggs, the same elevational band — 600–1,650 m — where the species is found year-round.
Conservation
The facts box carries the species’ current IUCN Red List category, Vulnerable. The main pressure on A. annae is habitat loss: forest clearance for coffee plantations, agriculture and urban expansion has fragmented its already limited Central Valley range into separated subpopulations, a pattern that increases the risk to the species even where individual populations still appear stable.
Similar species
A. annae is most easily confused with A. callidryas, the red-eyed treefrog, which shares a green body and orange-tinted feet but has bright red eyes and yellow-and-blue (not plain blue) flank bars. The golden eyes and Costa Rican cloud-forest range of A. annae are the clearest field marks separating it from its lowland, red-eyed relative.