An assessment of the abundance and distribution of the Titicaca Flightle

Summay

Censuses were conducted from 15 June to 6 July and from 15 to 24 October 2003 throughout Lake Titicaca to determine the current distribution and abundance of the Titicaca Flightless Grebe Rollandia microptera. We surveyed 22 of an estimated 25 local population distribution ranges. We defined these as shallow offshore feeding areas in combination with coastal beds of tule-rushes (Schoenoplectus tatora). At this large spatial scale we found variously sized populations of grebes in all 22 of the areas surveyed and a negative correlation between the total area of tule-bed within each area and grebe density. Absolute counts of grebes pooled across all sites produced a total of 2,582 individuals on Lake Titicaca. Given that some sites were either partially surveyed or not surveyed at all we feel that this is an underestimate of the total lake population. Limitations in methodologies used precluded the classification to development stage of approximately 43% of the individuals counted. Among the remaining 57% of the individuals counted we identified 732 mature adults within the total population of Lake Titicaca. When combined with information from other sources and current knowledge of habitat fragmentation our results support the classification of the species in the IUCN Red List as Endangered under criterion C2a. Of 20 local fisherman interviewed on the Bolivian side of Lake Titicaca, 90% confirmed that individuals of Titicaca Flightless Grebe incidentally drown in their fishing nets although responses varied from weekly to monthly estimates of by-catch. Although this study provides the first estimate of the total population of Titicaca Flightless Grebes on Lake Titicaca, a standardized monitoring programme will be required in order (1) to provide a baseline for the interpretation of future population trends in the context of impacts generated by human activities and (2) to aid in future management decisions for the long-term conservation of the species.

Introduction

Grebes are among the groups of aquatic bird species most sensitive to environmental change (O"Donnel and Fjeldsa° 1997). Their relative inability to disperse among aquatic habitats makes them susceptible to human impacts (Fjeldsa° 1984). The evolution of flightlessness in certain grebes has given rise to five highly range-restricted species in different parts of the world (O"Donnel and Fjeldsa° 1997, Llimona and del Hoyo 1992). Predictably these species are especially vulnerable to human-induced changes, as exemplified by the Juni´n Flightless Grebe Podiceps tackzanowski, a species endemic to Lake Juni´n in Peru and currently listed as Critically Endangered. Within the last 30 years alone, two species, the Atitla´ n Grebe Podilymbus gigas and Colombian Grebe Podiceps andinus, and possibly a third, the Alaotra Grebe Tachybaptus rufolavatus, have become extinct (BirdLife International 2004, O"Donnel and Fjeldsa° 1997, Llimona and del Hoyo 1992, Collar and Andrew 1988). On account of these trends and alarming anecdotal evidence, attention has recently been drawn to the Titicaca Flightless Grebe Rollandia microptera, a species endemic to the watershed of Lake Titicaca in the altiplano region of northern Bolivia and southern Peru (Hennessey et al. 2003).

A recent unpublished report indicated dramatic declines in several areas where studies and sightings have traditionally reported large numbers of grebes (Engblom et al. 2001). This assessment concluded that the species might be at risk of extinction. It has been suggested that the widespread introduction of monofilament fishing nets has led to the widespread decline of the species (Engblom et al. 2001, E. R. G. and D. F. A. pers. obs.). Others authors have cited the harvesting of reeds and indirect effects of fishing activities as long-term threats faced by the species (O"Donnel and Fjeldsa° 1997). However, despite the level of concern, there have been no previous studies evaluating the species" formal conservation status. We conducted the first formal large-scale evaluation of the species and its conservation status on Lake Titicaca.

Study area

Lake Titicaca is a high-altitude (3,810 m) tropical lake located in the Andean altiplano of Peru and Bolivia. The lake area is approximately 8,100 km2 and has three distinct regions: Lago Grande, Bahi´a Puno and Lago Chico (Figure 1). Because of its geographical location and large size, the lake maintains a relatively stable year-round climate. The altiplano has a dry season from April to November and a rainy season from December to March.

The flora and fauna of the lake are in large part supported by huge wetlands found along shallow sections of the shoreline, primarily within natural bays. The Titicaca Flightless Grebe is strongly associated with marsh beds comprised primarily of tule- rushes Schoenoplectus tatora. This species grows in depths of 1–4 m of water and emerges up to 2 m above the waterline, providing valuable foraging and roosting habitat for a number of aquatic bird species, among them the Titicaca Flightless Grebe (Fjeldsa° 1981). The emergent vegetation is dominated by Schoenoplectus tatora with other plant species such as Miriophyllium elatinoides, Lemna spp., Elodea spp. and Azolla spp. These other macrophytes can typically be found inhabiting various depth-bands, with a complex of Potamogeton spp. occupying the deepest band up to 9 m depth in Lago Chico and up to 14 m depth in Lago Grande (Iltis and Mourgiart 1982).