Distinct space-use patterns are associated with alternative reproductive tactics in lekking ruffs Calidris pugnax.
Spezie Giovanni G, Dinya Gergely G, Gelencsér-Horváth Anna A, Goymann Wolfgang W et al.
Territoriality is a key strategy through which animals secure access to reproductive opportunities, yet in many lekking species, males differ in their investment in defending space. Breeding aggregations often include territorial residents and non-territorial floaters, raising questions about the flexibility and endocrine regulation of alternative spatial tactics. The ruff (Calidris pugnax) provides a powerful model to address these questions because males occur as three genetically determined reproductive morphs: territorial independents and two non-territorial floater morphs, satellites and faeders. Using artificial intelligence-assisted tracking in a captive colony, we quantified fine-scale space-use patterns within experimental and control leks. Our aim was to test whether male morphs adjust spatial behaviour when social opportunities arise. Independents exhibited smaller and more segregated activity areas, whereas satellites and faeders showed larger, overlapping activity areas, consistent with a floater strategy. Despite experimentally manipulating lek composition to create single-morph social environments, neither satellites nor faeders adopted territorial-like spatial behaviour. In addition, circulating concentrations of testosterone were higher in independents than faeders and satellites, but short-term variation in testosterone was not linked to changes in spatial behaviour and experimental treatment. These findings support the view that space-use tactics in ruffs represent fixed specializations rather than flexible responses to social opportunities.