The Introduction of Love Birds (Agapornis) to Lake Naivasha, Kenya, and Their Effect on the Lake's Agriculture and Indigenous Avifauna

Abstract

Fieldwork was conducted between August 1985 and June ;_986 in the forest surrounding Lake Naivasha. The number of lovebirds was es t imat ed by both the fixed-width 1ine-transect and mar-k -r-eccp tur-e methods. There was good agreement between the v?rious estimn:es and the final population estimate for 95 per cent confidence was 5942 ± 612 lovebirds. The strengths and limitations of the methods are discussed in relation to over-or-underestimation of population size a.nd in relation to the results of previous workers. The present work provided a comparison of some bird census methodologies over a medium-sized area. Lovehirds were observed to initiate most of the avia.~ damage to .malze at Naivasha. Their strong bill and efficient technique of exposing kernels not only make the~ an important Dalze pest but also allows faster depredation by other species. At present, lovebirds have a relatively minor impact on commercial maize production SInce most ma i ze grown at Naivasha is intende d for consrnp t i on by cattle and harvested before being vulnerable. \'iorstdamage to ma i ze grown for human consumption was measured in small plots f'arried on a part-time basis. Large commercial fields we re either ade quat ely protected or too large for lovebirds to have a significant impact. Lovebirds were aggressed upon by many other speCIes and their behaviour is one of retreat rather than agg res si on . Love!:lirdsmay out-crnnpete other hole-nesting spe~les by more indirect methods xiii however. For example their modification and permanent inhabitation of nesting cavities. Primary moult was examined and no regular annual moulting periodicity could be detected. Since primary moult is linked with breeding, this could indicate their ability to breed at any time of the year at Naivasha. All lovebirds captured had intermediate hybrid characters although biased towards the fischeri phenotype. This bias is probably the result of an unbalanced genetic expression in plumage colouration rather than a difference in fitness of the fischeri genotype or the result of assortative mating.