Little Bustard Population Dynamics

Abstract

Little bustard populations have declined precipitously in many regions and countries of the western Palearctic, but they can also grow quite rapidly when conditions are favourable, reaching high densities from very low numbers in relatively few years. A few documented cases indeed indicate a marked exponential growth phase before they level off due to density-dependent effects. Population decreases also tend to be exponential rather than linear or slowly accelerated, for example when environmental conditions become adverse, which is a challenge for conservation since declines are usually faster than expected by managers, particularly in their initial stages. Thus, although the little bustard is a large and fairly long-lived bird, its capacity for fast recovery when favourable conditions are met makes the species a composite in the conceptual framework of K-r selection, showing both K- and r-selected traits. The population viability analyses (PVA) reviewed in this chapter indicate that little bustard long-term population persistence requires adult survival to be higher than 80%, fecundity higher than 0.9 fledglings per female, and sex ratio to stay between 0.3 and 0.5 males/total adult population. Population size should be also over 20 individuals, as density-dependent effects seem to be critical in little bustard population dynamics, likely in relation to lekking behaviour and constraints. For instance, a lek size below two males results in strong breeding depression, leading to increased risk of extinction in small populations due to the Allee effect. However, lekking also allows bustard populations to tolerate relatively small male numbers. PVAs further illustrate the relevance of connectivity in the species’ dynamics for both local populations and metapopulations. The latter seems to be adequately described by classic source-sink metapopulation models. Simulations also highlight the importance of guaranteeing a secure landscape matrix for dispersing birds, given the impact of mortality during the dispersal process. Little bustard population growth rates are highly sensitive to land use changes. Moreover, the impact of land management on little bustard breeding success and thus population growth may be modified by weather, particularly in Mediterranean regions. Consequently, conservation management should be adapted to forecasted climate changes.