When frogs in a field croak in chorus, they are not answering one another. They are in competition. Generally, only male frogs use their vocal sacs, which puff up like large balloons from their throats, to project their identity - distinct for every species - into the night.
They are in hopes that some yonder female will be attracted to their coaxing noise and hop to their sound. The females listen for the deepest croaks, which signify a bigger, fitter mate.
'But sometimes frogs are tricky,' says Teresa Ma, an ecologist by training who is doing research for her masters degree on frog habitats in Hong Kong.
Scientists say smaller frogs will call from within drainage pipes so their voices will amplify; average-sized frogs perch next to their particularly large brothers in the hope that if a female comes for the larger frog's call, they can try to intercept her or, if multiple females come, well, take advantage of the extra resources.
Every week during the mating season, usually from late February to September, Ma listens to frog calls in Long Valley, a 25-hectare stretch of wetland in the New Territories and home to many of Hong Kong's competing frogs.
The frogs are lucky there: they call in the midst of 400 fields reserved for small-scale farmers in a unique collaboration between the farmers, the Conservancy Association and the Hong Kong Birdwatching Society. The farmers receive cash from the non-government organisations (NGOs) to compensate for money lost while growing diverse crops instead of traditional agricultural practices which usually focus on cash crops.