Surveys are very important tools for population monitoring, conservation and species management. Censuses aid in the sustainable harvesting of game species. Our aim in this study was to test whether some factors related to habitat and agricultural practices of olive cultivation may influence red-legged partridge abundance estimates. We investigated the effects of time of day and season of the year in which censuses are conducted, as well as of the reduction of herbaceous cover and the installation of irrigation systems, on red-legged partridge abundance estimates. In surveys conducted in winter, no differences were found in the estimates of abundance and density between partridge censuses at dawn and dusk. In surveys conducted in summer, the estimates made at dusk were significantly higher than those at dawn. The coefficients of variation of the estimates were lower at dusk in the two seasons. In winter, partridge abundance was not related to any of the factors studied. However, in summer partridge observations were related to the distances to the border of the olive grove, where herbaceous vegetation persists, and to water sources. There was an interaction between the time of the census and the habitat preferences of partridges. During the morning, partridges were more active and moved towards the borders of the grove. At dusk partridges were less active and returned to the olive grove. The results suggest that habitat use by red-legged partridges undergoes spatial and temporal adjustments in olive groves that seem to be related to some habitat features of the groves associated with agricultural practices. The temporal and spatial behaviour of the birds in the groves can influence the accuracy of surveys. Differences in the results of censuses carried out at dawn and dusk indicate that the two may not be comparable and suggest the need to take time of day into account when designing a survey.
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