Dispersal patterns of the endangered Crested Ibis suggest high breeding densities drive natal dispersal

Abstract

Abstract Although dispersal is a key driver of population dynamics and species distributions, we still know little about how it affects the dynamics of endangered and restricted-range species. Density-dependent effects on dispersal in particular may be critical for the range expansion of recovering populations. After 1981, when the last 7 wild individuals of Crested Ibis (Nipponia nippon) were discovered in China, the species remained confined to a single location (“original nesting area”) until 2000 (<24 breeding pairs). Then, the breeding population began a significant spatial and numerical expansion toward new breeding sites (“secondary nesting areas”). Our analyses of long-term (1993–2017) individual resighting data (n = 193) found that natal dispersal was common (~77.2%), whereas breeding dispersal was rare (~2.1%). Breeding density was negatively related to productivity, and natal dispersal was more likely toward low-density areas. The Weibull distribution provided the best fit to the observed dispersal distances, indicating the presence of long-distance natal dispersers. Although we cannot rule out the effect of dispersal mechanisms inherent in the species regardless of density, our findings suggest that the probability of natal dispersal is density-dependent, implying a role for intraspecific competition in the Crested Ibis spreading in the region. We expect the Crested Ibis to spread throughout the region if conservation programs can identify and protect potential reintroduction areas at a large spatial scale to allow dispersing Crested Ibis to settle into new and low-density breeding areas.