Ecological drivers of songbird stopover behaviour during autumn migration in eastern New Brunswick
Abstract
As songbirds migrate, they must periodically stop to rebuild the energy needed for flight. Individual traits, local habitat characteristics, and the surrounding landscape can affect stopover refuelling and movement, yet the relative importance of endogenous and exogenous factors and the interrelation between refuelling and movement is less well understood owing to the challenge of measuring these aspects concurrently in free-living songbirds. I applied physiological profiling and habitat assessment together with radio telemetry and radar technologies to evaluate key ecological drivers of stopover performance in songbirds. In my first research chapter, I evaluated how refuelling and diel activity differed among five species, testing the hypothesis that refuelling intensity facilitates longer migration. Greater refuelling was associated with longer migration distances after accounting for the negative relationship between refuelling rate and the species-specific onset time of diel activity. In my second research chapter, I combined site-level measurements of invertebrate and migrant abundance with measures of refuelling and behaviour at coastal and inland stopover sites to assess how local habitat, landscape, and individual traits affect stopover performance. Songbird abundance was positively associated with invertebrate abundance, likely resulting from the earlier departure of birds experiencing poor refuelling at arrival. Behaviour and refuelling did not differ between coastal and inland stopover sites. In my third research chapter, resource augmentation was used to experimentally test if food availability affects refuelling and movement differently in the age and morph classes of the White-throated Sparrows (Zonotrichia albicollis). White-striped birds had greater refuelling when resources were augmented, but stopover behaviour did not differ according to treatment. In my final research chapter, I used radar and acoustic monitoring to test if visual and auditory information from volant migrants acts as a cue for departure, and whether sensitivity to these cues differs by age. Departure behaviour was not influenced by the passage of migrants nor by the number of night flight calls, but occurred earlier when wind conditions were more energetically favourable. Together, these studies provide insights into the relationships between refuelling, movement behaviour, and the environment that further our understanding of the migratory stopover behaviour of songbirds.