Abstract from: Leu, M. 2000. Breeding territory settlement patterns and mate choice in a monochromatic Tyrannid flycatcher. Ph.D. dissertation. University of Washington, Seattle WA. 129 pp.

What factors influence a male’s ability to acquire a high-quality territory and what cues do females use to select a mate in the monochromatic Pacific-slope flycatcher (Empidonax difficilis)?  I addressed this question by showing that territory settlement patterns occur “preemptively” on the breeding grounds along a habitat-quality gradient defined by red alder (Alnus ruba) and preferred nesting substrate (adventitious nest substrate) densities.  Early arriving adult males excluded later arriving males, including yearling males, from gaining access to high-quality habitat.  Acquisition of high-quality territories was influenced by arrival time, which in turn was influenced by body condition and fat scores.  Once on the breeding grounds, males in high-quality habitat were not repeatedly challenged by males arriving later on the breeding grounds because there was no difference among habitat quality types with regard to territorial defense song rate, testosterone and corticosterone plasma concentrations, and response time to simulated territorial intrusions.  Upon arrival, females differentiated among habitat quality types by selecting habitat according to presence of red alder and/or male body condition.  Song behavior, testosterone plasma level, and response time to territorial intrusions did not correlate with pairing date.  To discern whether territory quality is important in female territory settlement patterns, I removed the preferred nest substrate in treatment plots, thereby altering territory quality.  This experiment showed that the availability of preferred nest substrate seemed not to play a role in female settlement patterns in high-quality habitat instead females seem to select territory quality according to a hierarchical process.  Upon arrival, females selected habitat at the macro scale (i.e., presence of red alder) but as they geared up for breeding, the habitat selection process was fine-tuned.  If a territory lacked preferred nest substrate, females abandoned their mates more frequently in treatments than controls.  Abandonment of males occurred when females started to build nests because the lag between pairing and abandoning of mate was not different from the lag between pairing and initiation of first clutches in successful pairs breeding in treatments and controls.  This suggests that female territory settlement patterns in Pacific-slope flycatchers may be adjusted throughout the pairing phase.