Nest-site selection in a terrestrially breeding frog with protracted development

Abstract

Metamorphosis of larvae of the Australian moss frog (Bryobatrachus nimbus) occurs in a terrestrial nest approximately one year after oviposition. Neither parent attends the eggs, thus selection of an appropriate nest site is critical to egg viability. This study examined the dynamics of nest-site utilisation over six years and the characteristics of nests chosen as oviposition sites. Nest cavities were located at ground level amongst heath within one of 10 species of bryophyte, lichen and lycopod. On average, 2.6% of nests contained a male B. nimbus during daytime monitoring during the breeding season, and 7.3% of nests contained an egg mass. Despite an abundance of potentially suitable nests from previous years, males constructed a small proportion (<10%) of new nests each year and new nests were more likely to be used as oviposition sites than older nests. Discriminant function analysis showed that moss nests used as oviposition sites were distinguishable from empty nests by their greater horizontal dimensions. Eggs deposited in wider nests are restricted to fewer layers, and a preference for wider nests may be adaptive because embryonic oxygenation is enhanced under such conditions. However, rather than demonstrating nest-site selection, the use of relatively large nests as oviposition sites may be an artifact of their occupancy by a breeding pair.