A study of California quail in New Zealand with particular reference to population ecology

Abstract

California quail, probably Lophortyx californicus brunnescens, were first liberated in New Zealand in 1962. The species’ geographical range and habitat types are described.

A general account then follows of local diurnal and annual activity rhythms and other phenomena including roosting behaviour, covey formation, sub covey composition and home range, emigration and immigration. Male and female reproductive cycles and aspects of breeding season ecology – including clutch size, nest (nesting) success, fertility and hatchability of eggs – likely to limit quail umbers have been studied and found to have no significant correlations with the population fluctuations. After describing methods used for fixing breeding season phenology, local and annual variations in phenology have been compared and found to lack consistent correlation with the degree of success of the breeding season and subsequent population density. Contrary to expectation, breeding in the North Island appears to start later than in the South Island. This at present cannot be explained. Hatching periods are the same length in each island – 13 weeks – which implies a breeding season of about 4 ½ months duration in New Zealand. The main method used for obtaining these figures is that of a post-dating from trapped samples of juvenile quail aged by a study of growth of primaries. Methods used for studying population density and its changes have included trapping, marking and recapture, a shooting diary scheme and, in one locality, direct enumeration. The main index used for measuring population density has been age ratio (young per 100 adult females). This method has been supplemented by use of sex ratios, analysis of sportsmen’s opinions of abundance and the series of total counts referred to above. All give similar results. Fluctuations in South Island populations cyclic over a number of years (periodicity of 4 years) and synchronous over a wide area. North Island fluctuations were neither cyclic nor synchronous with those of the South Island. Relationships between weather and breeding season phenomena were explored and no correlations found. However, very wet sprints or early summers may be detrimental to survival of young. Though growth rates of young are not reflected in preceding or subsequent population densities, there are indications that peak years are associated with changes in the representation and distribution of weight classes and the presence of heavy adult females in winter. Food supply or quality does not appear to be implicated. Some attention has been given to the quantitative study of predation, parasitism and the contributions of hunting and accident to morality. None of these factors shows a clear correlation with the population fluctuations except, possibly, the incidence of coccidiosis. Mortality rates have been measured for the various age and sex groups. Methods used have included the construction of life tables from band recoveries or retrap data (in the latter using both deterministic and stochastic techniques), the use of age ratios and, in one locality, a series of successive censuses. All these methods are critically discussed. Results indicate a mortality rate for all birds of 60-70 percent in populations that are shot and less those not shot. Rates for immature exceed those of adults, adult females those of adult males and those immature males equal those immature females. Productivity of young is higher in shot than in unshot population. Age ratios obtained by shooting in New Zealand are generally much lower than those obtained similarly in the United State and possible reasons for this have been explored. An estimate has been made of the contribution of shooting mortality to total mortality. The question of whether quail populations fluctuate randomly or are controlled is considered and evidence advance that fluctuations are density-dependent. The critical period for regulation appears to be in the immediate post-hatching period and takes the form of density-dependent regulation of juvenile and adult female mortality. Modification of the effective birth rate appears unimportant. The regulating factor is so far unknown but may be genetic. The cyclic fluctuations seem to have arisen mainly by chance and weather is probably the synchronizing agent.