• Abundance;
  • developmental stability;
  • fluctuating asymmetry;
  • habitat suitability;
  • position within the range

A central question in ecology is how individual fitness interacts with the spatial variation in population density and habitat characteristics across species’ ranges. We used fluctuating asymmetry (FA) as a measure of developmental stability (DS) in individuals of Tyrannus forficatus to estimate the suitability of sites of varying abundance and position within the species’ range. FA in the inner-tail feathers of males and females is not spatially correlated across the species’ range. FA in males increases towards the centre of the range and is not correlated with abundance. FA in females is not correlated with position in the range or abundance. Our results suggest that optimal sites are found throughout the range of the species, whereas suboptimal sites are mainly found towards the centre of the range. Additionally, our results suggest that abundance may not reflect the suitability of sites across species’ ranges.