Rapid Assessment Survey of the Endangered Silver Bladder Reed Frog (Hyperolius Cystocandicans) in Southern Slopes of Mount Kenya Forest

Abstract

Reed frogs are a good case for investigating diversity of reproductive traits associated with co-occurrence, resource partitioning and habitat heterogeneity. Objectives of this study were to: (1) establish patterns of co-occurrence and spatial distribution among frogs in relation with characteristics of habitat patches; (2) identify the distance from water, spacing between conspecifics and perching height of silver bladder reed frog (Hyperolius cystocandicans) and other reed frogs, and; (3) estimate the population sizes and density of reed frogs in the forest on Southern Slopes of Mt. Kenya. Frogs were searched opportunistically through visual encounter surveys and acoustic encounter surveys, complemented by use of drift fences and pitfall traps with funnel traps. Capture mark recapture method was used to generate individual capture history file that was used to estimate population sizes, capture probability, probability of entry and probability of apparent survival using POPAN Jolly Seber model in MARK. Co-occurrence was estimated using pairwise probabilistic model of species cooccurrence using presence-absence data. The results of this survey showed that H. cystocandicans co-occurs positively with Amietia nutti, Hyperolius glandicolor, Hyperolius montanus and Phrynobatrachus kinangopensis and randomly with Ptychadena mahnerti, Kassina senegalensis, Sclerophrys kerinyagae and Xenopus borealis. There was interspecific variation in height and spacing of egg masses of H. cystocandicans and H. montanus but both species deposited their eggs away from water (terrestrial eggs). Interspecific variation was established in the height of perching adult reed frogs (H. glandicolor, H. cystocandicans and H. montanus) but not distance of perching site from water and spacing between conspecifics. The population sizes of reed frogs per site were: H. glandicolor (123±20.05, 154±99.86, 162±14.85), H. montanus (308±52.12, 50±23.30, 133±10.80; H. cystocandicans (194±18.24, 101±6.43, 298±38.07). Population estimates were skewed towards males in H. cystocandicans and H. montanus but not H. glandicolor. With the exception of H. montanus, the estimated population densities of H. cystocandicans and H. glandicolor did not vary across survey sites. Population densities did not vary significantly across species. All species have aquatic larvae but H. glandicolor has aquatic oviposition site which differs with terrestrial oviposition sites of H. montanus and H. cystocandicans. It was concluded that this variation drives spatial reproductive partitioning in distribution of reed frogs in breeding sites which was explained by interspecific difference in spacing between egg masses, distance of egg masses from water, height of perching adults and height of egg masses. This study provides baseline population data that will inform conservation of reed frogs. There is need for further estimates to determine whether the populations are declining. Future research should explore genetic diversity in order to estimate the effective population size and operational sex ratio in male-biased populations.