The feeding ecology, productivity and management of Starlings in Canterbury, New Zealand.
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The starling Sturnus v. vulgaris L. is native to Western Europe, but through liberation now occurs widely throughout North America, South Africa, Australia and New Zealand. The species became established in New Zealand following nation-wide liberations between 1862 and 1883 (Thompson, 1922), and by 1895 occurred in immense flocks in nearly all districts (Kirk, 1895). In Canterbury, birds were liberated by Acclimatisation Societies in 1867 (20) and in 1871 (40) (Thompson, op. cit.). At approximately the same time, many birds were released by private citizens and starling numbers increased rapidly. Since that time the natural aggressiveness, adaptability and capacity for rapid colonization inherent in the species have led to its present widespread distribution in lowland Canterbury. Apparently, starlings captured in Britain formed the bulk of birds liberated in New Zealand. However, birds from this source have been considered to show "marked differences in the degrees of development of their reproductive systems", and the existence of two local races has been postulated (Bullough, 1942) viz. a resident early-breeding British bird and a later breeding migrant European form. Amadon (1962) disagreed with this thesis and considered the Continental and British birds to be identical, and referred them to Sturnus v. vulgaris L. Although both "races" may have been included in the stock introduced into New Zealand, the Canterbury population appears to be phenotypically uniform. Starlings are ubiquitous on farmlands of many countries and, because of their varied diet, have been frequently studied. Starling foods, feeding habits and breeding biology have been examined in detail in North America (Kalmbach and Gabrielson, 1921; Lindsey, 1939; Kessel, 1957; Howard, 1959), Australia (Thomas, 1957 a-e) , Great Britain (Collinge, 1924-27; Dunnet, 1955, 1956) and Europe (Kluijver, 1933; Szijj, 1956; Shlapak, 1961; Karpovich, 1962; Pfabe and Szypul, 1964; Havlin and Folk, 1965; Gromadski, 1969). There has been little work done on this species in New Zealand above anecdotal levels, but several research programmes are currently in progress e.g. Ecology Division, Department of Scientific and Industrial Research (D.S.I.R.), is studying the breeding biology and inheritance of clutch size in the Wellington area and its feeding and breeding biology at Havelock North. Published research includes a cursory study of starling foods and feeding on the Wellington and Gisborne airfields (Caithness, 1968), damage to fruit in New Zealand orchards (Dawson and Bull, 1970), and a list of the food species identified from the faeces of a group of Mid-Canterbury starlings (Lobb and Wood, 1971). The manipulation of starling populations in conjunction with stock as agents in biological control programmes has also been documented (Anon, 1970). Unpublished theses include the foods and daily movements of starlings on Harewood Airport, Christchurch (Moeed, 1970) and, predation on populations of Costelytra zealandica, a scarabaeid beetle (East, 1972). Starlings may be beneficial or detrimental to agriculture depending on whether any increase or reduction in farm production results from their activities. In the mixed farming areas of Canterbury the feeding activities of the starling are diverse; the province includes the main cereal growing region of New Zealand and has extensive grasslands which frequently have high density populations of Costelytra zealandica White. This common food item of the starling (Anon, op. cit.; Lobb and Wood, op. cit.) is a serious economic pest, as it causes extensive damage to pasture grasses. Many farmers believe that starlings may partly control this invertebrate, and this has also been suggested by Dr R. East, an entomologist (cited by Bloxham, 1968). Recent laws controlling the use of once liberally applied insecticides have stimulated some farmers in Canterbury and elsewhere to erect nest-boxes throughout their farms, in attempts to entice and hold starlings on their properties. However, while the starling is the commonest bird species on most farmlands of New Zealand, much of its feeding ecology in this country is poorly documented. Studies of its food in other countries have shown that the species takes a wide range of pastoral invertebrates, but also severely reduces stocks of grain and fruit. It is therefore of great importance that all aspects of the local ecology of the starling should be fully documented, before the species is considered for manipulated biological or integrated control programmes. The aims of this study were, in order of priority: (1.) to assess the foods and feeding biology of a population of starlings in a mixed-crop-livestock farming area of Canterbury, (2.) to evaluate the species productivity and demography, and (3.) to investigate the feasibility of manipulating local starling populations, with the view of capitalizing on their expected selected predation of certain invertebrates harmful to local agriculture. Simultaneously, an associate study was made at Lincoln College, New Zealand, by Dr R. East (for details, see above); both studies have been instigated and partly financed by the New Zealand Department of Scientific and Industrial Research. The first part of this thesis deals with methods of sexing and ageing starlings and population statistics. Subsequent sections, in order, deal with starling population management, demography, breeding biology, foods and feeding biology and changes in body weight.