Factors affecting foraging and reproductive success of Kittlitz’s Plover (Charadrius pecuarius TEMMINCK) at two soda lakes in eastern Rift Valley, Kenya

Abstract

Ground nesting shorebirds are perennially at risk from an array of threats arising from activities of humans, other animals and climate induced factors. People and wild animals can destroy nests and kill young birds as well as cause direct and indirect disturbance on shorebirds. Climate variability influences the hydrological cycle thereby causing changes in lake water levels and the extent of the shorelines in aquatic ecosystems. Lakes Nakuru and Elmenteita situated in Kenya’s Rift Valley are internationally important for the conservation of shorebirds and are facing the pressures of increase human activity and climate variability. This study investigates how these factors influence the foraging and breeding success of Kittlitz’s Plover (Charadrius pecuarius TEMMINCK) at these two lakes. Specific objectives were to determine the population size, potential food and foraging behaviour as well as assess the breeding performance of the Kittlitz’s Plover. The study established that Lake Nakuru and Lake Elmenteita support a maximum of 544 and 124 birds respectively giving a total estimate of 668 birds. The two sites combined give a long term mean (±SD) population of 285.3 ± 162.6 birds, which is approximately 0.29% of the world population of the species. An assessment of invertebrates, as potential food for the Kittlitz’s Plover using pitfall traps, identified fourteen taxonomic families in six orders of Arthropods. Coleoptera comprising 96% and 89% of all the invertebrates captured at Lakes Elmenteita and Nakuru respectively were the most abundant potential prey. The foraging rates were significantly higher in areas with low human disturbance. The mean (±SD) Foraging Effort (i.e. number of steps made per individual in 30 seconds while foraging) at Lake Nakuru was 34.83 ± 9.74, which was significantly higher (Mann-Whitney U = 1373.5, n = 63, P = 0.003) than that of Lake Elmenteita (30.95 ± 9.36). The mean (±SD) Foraging Efficiency (i.e. number of pecks made per individual in 30 seconds while foraging) was also significantly higher at Lake Elmenteita (9.24 ± 4.11) compared to Lake Nakuru 7.24 ± 4.11 (Mann-Whitney U = 1381.5, n = 63, P = 0.003). The mean (±SD) Food Intake rate (i.e. number of swallows made per individual in 30 seconds while foraging) was also higher in Lake Elmenteita (4.70 ± 2.41) than Lake Nakuru (3.70 ± 2.41) (U = 1506.5, n = 63, P = 0.019). Overall, the birds at Lake Elmenteita experienced higher food availability, spent less energy feeding and achieved higher foraging success rate compared to those resident in Lake Nakuru. Nesting success of Kittlitz’s Plover was highest in medium level disturbance areas and lowest in areas of highest human activity. The main causes of nest failure were flooding (52%), vehicle damage (36%) and predation (12%). Using the Mayfield nest loss estimator, Lake Elmenteita had higher nesting success rate (43%) than Lake Nakuru (37%). The combined nest survival rate for the two lakes was 41%, which indicates that the two sites were still good for breeding by Kittlitz’s Plover. Results of this study revealed no significant difference between the two lakes in the number of nests built, eggs laid and chicks hatched. Lake Elmenteita contributed significantly more chicks (72.7%, 48/66) compared to Lake Nakuru at 27.3% (18/66). The mean (± SD) number of tourist vehicles (21.7 ± 42.7) and people (6.3 ± 17.0) walking per kilometre of shoreline per day, was higher at Lake Nakuru compared to Lake Elmenteita where no tourist vehicles were recorded. The mean (± SD) number of wild mammals, including predators, in the Kittlitz’s Plover habitats at Lake Nakuru was estimated at 23.2 ± 58.0 per kilometre of shoreline per day. The frequency of human, herbivore and predators’ foot prints, tyre marks and dung piles revealed higher disturbance levels at Lake Nakuru by large mammals (64.1%), humans (81.7%) and vehicles (92.9%) than at Lake Elmenteita where the frequencies of those threats stood at 35.9%, 18.3% and 7.1% respectively. The upward trend in visitor numbers, especially at Lake Nakuru and growing settlements around Lake Elmenteita, envisage increased human disturbance along the lake shores. The changes in climatic conditions envisage increased occurrences of flooding and drought. The study recommends instituting mitigation measures such as increased awareness about the breeding birds, zoning of the shoreline for visitors and digging of trenches to curb human disturbance and climate impacts, and conserve the nesting birds.