The introduction of lovebirds (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 1986 in the forest surrounding Lake Naivasha. The number of lovebirds was estimated by both the fixed-width line-transect and mark-recapture methods. There was good agreement between the var i ous estimates 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 and in relation to the results of previous workers. The present work provided a comparison of some bird census methodologies over a medium-sized area. Lovebirds were observed to initiate most of the avian damage to maize at Naivasha. Their strong bill and efficient technique of exposing kernels not only make -them an important maize pest but also allows faster depredation by other species. At present, lovebirds have a relatively minor impact on commercial maize production since most maize grown at Naivasha is intended f or- consumption by cattle and harvested beforebeing vulnerable. Worst damage to maize grown for human consumption was measured in small plots farmed on a part-time basis. Large commercial fields were either adequately 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 aggression. Lovebirds may out-compete other ho le+ne st ing spec i.e s by more indirect methods however. For example, their modification and permanent inhabitation of nesting cavities. Primary moul t 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.