Structure and diversity of cloud forest bird communities in Alta Verapaz, Guatemala, and implications for conservation.

Abstract

In a 102 ha study plot in the Sierra Yalijux, Alta Verapaz, Guatemala (90° 03 W, 15° 22 N, 1980 2550 m) the bird community was observed with standardized mark-recapture and transect census methods within natural and natural-like pine-oak cloud forest and secondary vegetation.The study plot consists of two compartments with equal areas of natural (near primary) vegetation and young secondary forest (approximately 5 years old). The latter is a result from slash-and-burn agriculture. Special emphasis was made to analyze whether secondary vegetation is suitable to preserve a comparable amount of diversity of natural forest. Different approaches were made to test the differences. Diversity, species richness, evenness, body mass distribution, recapture rates, territoriality, guild structure, abundance of specialists and endemics were used to compare both compartments. While diversity and species richness are lower in natural forest than in young secondary forest, evenness, body-mass distribution, recapture rates, territoriality, abundances of specialists and endemics are higher in natural forest. Guild composition was significantly different concerning both habitat types, i.e. insectivorous birds were more frequent in natural forest in both species and individual numbers compared to secondary vegetation. On the other hand in young secondary vegetation, granivorous birds were more frequent concerning the same parameters.While species richness (in total 99 observed species within the 102 ha plot) was higher in secondary vegetation (63 species) than in natural forest (56), this is not advantageous considering conservation regarding the further parameters evaluated (see above). The body mass of the birds is, both on species and individuals level, higher in natural forest than in young secondary forest because of the better nutrition resources in the first habitat type. Furthermore, recapture rates and abundances are comparable higher in natural forest than in young secondary forest (955 and 538 respectively, both in relation to each 51 ha of the total study site area). Consequently, there are more possible territories in natural forest.Because of the analyzed parameters mentioned above, it is visible that young secondary forest is not suitable to preserve natural like structures of forest bird communities.The situation of specialists and endemics was evaluated more precisely using the basic data mentioned before. Central American highland endemics are mainly present in natural forest and are reproducing mainly here. E.g., the Resplendent Quetzal (Pharomachrus mocinno) will disappear after a relaxation time of 50 years following the complete destruction of the natural forest at the study site. The population survival of this species on a long term is dependent on the characteristic rotten tree stumps, which emerge only in natural forest.Furthermore, the species-area-equilibrium for the Central American highland endemics (21 species in total from EBA # 018; Stattersfield et al. 1998) is not yet reached and ten out of the 13 observed endemics will vanish, even when destruction of the natural forest will stop immediately.Compared to different sites (to evaluate weather or not the study site has similar high species numbers like biodiversity hotspots in mountainously regions or lowland hotspots) in lowland Panamá (Robinson et al. 2000) and Amazonia in eastern Perú (Terborgh et al. 1990), the Chelemhá plot is in terms of diversity more similar to highland bird communities in Ecuador (e.g., Poulson & Krabbe 1997) or temperate sites in North America (e.g., Karr 1971). Nevertheless, evolutionary speaking, 13 out of the 28 families of the Chelemhá plot are Neotropical or South American elements, the remaining 15 are cosmopolitan or North American.Because natural forest is advantageous to secondary vegetation concerning abundances, body mass distribution, proportion of specialists and endemics, it is highly recommended to preserve the natural forest fragments in the Sierra Yalijux. In particular, for the two target species, Resplendent Quetzal Pharomachrus mocinno and Yucatán Black-Howler Monkey Alouatta pigra, the forest remnants are essential for long-term survival.Thus, the conservation of the natural forest remnants is necessary to preserve species like the Resplendent Quetzal from extinction.