Data from: Morphological traits are not consistently related to population size in four migratory caribou populations across North America

To develop effective management to maintain or restore populations of
large herbivores, wildlife managers require sound empirical data on their
variations in size and associated parameters. Many studies have
highlighted links between morphological traits of individuals and
population density; however, less attention has been devoted to whether or
not morphological traits can reliably inform on population size in years
when no population estimates are available. We evaluated the relationships
between three morphological traits (hind foot length, body mass, and body
fat) and population size interpolated over three decades, for four
migratory caribou (Rangifer tarandus) herds in northern Canada and Alaska.
Our sample included 8,865 measurements of 4,473 individuals. We used a
Bayesian modelling approach to evaluate the relationships between
morphology and population size across different sex and age classes,
considering different temporal scales and, when possible, phases of
population growth or decline. We found that morphological traits were not
consistently linked to population size. Statistically significant
relationships existed for some combinations of herd and age classes, but
weak to absent relationships were more common. Our study suggests that
morphological traits alone cannot replace data obtained from aerial
surveys to approximate population size when population trends are unknown.
We discuss the usefulness of morphological traits to explain population
size, and recognize their role as complementary metrics to inform the
management and conservation of large herbivore populations, but conclude
that generally morphological data should not be used to predict population
size without prior information on population trends.