Elevational replacement of two Himalayan titmice: interspecific competition or habitat preference?

Elevational species replacement is a widely documented pattern in montane species. Although interspecific competition has been shown to be important in setting species elevational limits in tropical habitats, its effect in species of temperate regions is poorly studied. We tested the role of interspecific competition for space in the breeding season and for food in the non-breeding season in mediating the distribution of two resident titmice species in the Himalayas. We show that high elevation green-backed tits Parus monticolus are behaviourally dominant over low elevation cinereous tits Parus cinereus in both song playback and feeder trials. Despite being subordinate, at their elevational upper limit, cinereous tits occur in sympatry in human modified habitats. Our study suggests that the loss of natural habitats in the sympatric zone, not interspecific competition, might be limiting the distribution of the high-elevation green-backed tits and facilitating an upward range shift through human association in cinereous tits.