Response of least flycatchers Empidonax minimus to forest disturbances

Abstract

Least flycatcher Empidonax minimus distributions were studied in northern Michigan (USA) from 1984-1985 in large (> 100 ha) continuous hardwood forests adjacent to forest disturbances of 0[middle dot]8-21 ha. This species occurred in dense aggregations ranging from 3[middle dot]06 to 8[middle dot]71 birds ha-1. Flycatcher response to forest disturbances was evaluated by measuring the distance from the perimeter of an aggregation to the nearest forest opening and by monitoring breeding bird density within aggregations near disturbances. A gradient in flycatcher response to forest openings is hypothesised, ranging from no changes in breeding bird density and spatial distribution of aggregations near small disturbances to reductions in breeding bird density and spatial shifts in aggregations into the forest interior for large disturbances. A significant positive relationship was obtained for size of a forest opening and the distance aggregations were displaced into the forest interior. Displacement distances asymptotically levelled off at 200 m for openings >= 10 ha. No relationship was found for breeding bird density and forest opening size. Vegetative comparisons of utilised and unutilised habitat indicated that a well-developed canopy and large-tall trees may be important in the selection of habitat by aggregating flycatchers.