Data from: An empirical and mechanistic explanation of abundance-occupancy relationships for a critically endangered nomadic migrant

The positive abundance-occupancy relationship (AOR) is a pervasive pattern
in macroecology. Similarly, the association between occupancy (or
probability of occurrence) and abundance is also usually assumed to be
positive and in most cases constant. Examples of AORs for nomadic species
with variable distributions are extremely rare. Here we examined temporal
and spatial trends in the AOR over seven years for a critically endangered
nomadic migrant which relies on dynamic pulses in food availability to
breed. We predicted a negative temporal relationship, where local mean
abundances increase when the number of occupied sites decreases, and a
positive relationship between local abundances and the probability of
occurrence. We also predicted that these patterns are largely attributable
to spatiotemporal variation in food abundance. The temporal AOR was
significantly negative and annual food availability was significantly
positively correlated with the number of occupied sites, but negatively
correlated with abundance. Thus, as food availability decreased, local
densities of birds increased, and vice-versa. The abundance - probability
of occurrence relationship was positive and non-linear, but varied between
years due to differing degrees of spatial aggregation caused by changing
food availability. Importantly, high abundance (or occupancy) did not
necessarily equate to high quality habitat and may be indicative of
resource bottlenecks or exposure to other processes affecting vital rates.
Our results provide a rare empirical example that highlights the
complexity of AORs for species that target aggregated food resources in
dynamic environments.