U.S. Geological Survey Home Page USGS Patuxent Wildlife Research Center Science Meetings; dedicated to Chandler S. Robbins USGS Patuxent Wildlife Research Center; Science Meetings dedicated to Chandler S. Robbins Dedicated to Chan Robbins USGS Patuxent Wildlife Research Center; Science Meetings dedicated to Chandler S. Robbins Poster Abstracts from USGS Patuxent Wildlife Research Science Meetings, October, 2006
Patuxent Science Meeting 2006 Poster Abstract

Behavior and Ecology of the Alder Flycatcher (Empidonax alnorum) in

early winter

Foster MS

Before the status and vulnerability of a species can be accurately assessed and an effective

management plan for its protection developed, year-round threats to its well being must be

considered. Yet information about the biology of Nearctic migrant birds during migration and on

their wintering grounds is scarce. The Alder Flycatcher (Empidonax alnorum) is one of the

species for which migratory and winter behavior and ecology are especially poorly known.

These birds winter on the eastern slopes of the Andes and into the adjacent lowlands from

central Colombia south into northwestern Argentina. They occupy shrubby clearings, open

woodlands, and dense brush, especially adjacent to water, as well as primary-succession

habitats along the shores of floodplain rivers. I studied the early winter ecology and behavior of

Alder Flycatcher along a white-water meander river in Manu National Park, Peru during October

and November from 1993 to 1997. The birds occupied territories in the primary-succession

habitats on growing point bars. They were most common in mixed stands of Tessaria integrifolia

(Asteraceae) and Gynerium sagittatum (Gramineaceae) interspersed with bare sand areas. The

uneven height of the Tessaria canopy, which resulted in openings in the vegetation large

enough for the birds to flycatch, was an important habitat feature. Birds obtained insects

primarily by aerial hawking (91%). Fruit formed four percent of the diet. Territories ranged from

0.04 to 0.25 ha and were occupied by one, two, or three birds. Every territory had one

dominant individual who was primarily responsible for territory defense; the other birds were

subordinate. Vocalizations given included the fee-bee-o song, a two-syllable song, and the pit

note, which are also given on the breeding grounds. A series of pits given increasingly rapidly

signaled a territorial interaction. In the least aggressive encounters, the birds remained on their

territories and countersang or exchanged agitated calls. In boundary disputes the birds engaged

in a vocal duel at a common territorial boundary. In the greatest intensity interactions

dominants chased intruders out of the territory. Dominant birds, which sang the full song, likely

were adult males. Immature males do not sing a full song, and females are not known to sing in

nature. Subordinate individuals were likely females or young males. At present, Alder

Flycatcher populations show no evidence of declines. However, the behaviorally dominant

Willow Flycatcher appears to be expanding its breeding range northward, displacing the Alder,

whose breeding range is shrinking. Loss or degradation of riparian habitats could also become a

factor on both the breeding and wintering grounds. The floodplain habitats along meander rivers

in the Amazon Basin, which are renewed each year by depositions of silt, are highly fertile and

suitable for agriculture. In addition, plant species (particularly Tessaria) characteristic of the

primary succession are especially fast growing and produce fiber suitable for paper pulp.

Because these primary succession habitats are constantly being renewed, however, it may be

possible to develop land-use plans in which only the post-Tessaria successional stages are

Friday, September 22, 2006

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