Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Biology

Supervisor

Morbey, Yolanda E.

2nd Supervisor

Guglielmo, Christopher G.

Joint Supervisor

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.

Summary for Lay Audience

As songbirds migrate between nesting and wintering areas, they must stop to rest and rebuild the energy needed for flight. Individual traits, such as which species it is or whether it is a young or old migrant, as well as external factors such as food availability and the suitability of conditions to migrate, can influence how long migrants spend at a stopover site. Due to the challenge of measuring these aspects in wild songbirds, whether individual traits or external factors have a greater impact on behaviour and refuelling, and how refuelling may influence behaviour is unclear. To further our understanding of songbird migration, I combined measurements of local food availability and bird abundance with measurements of individual refuelling and behaviour. I first looked at how refuelling and daily activity patterns differed among five study species. As anticipated, species that migrated longer distances were active earlier, refuelled faster, and remained for a shorter amount of time at a stopover site. I next looked at how food availability, the number of birds using a site, and individual traits such as age influenced refuelling and behaviour at coastal and inland stopover sites. More birds were captured at sites when more food was available, and migrants that experienced poor refuelling shortly after arrival were quick to leave a site. Behaviour and refuelling did not differ between coastal and inland stopover sites, suggesting that birds can use each region equally well during migration. I then built on this study by experimentally testing the effect of food availability on the refuelling and behaviour of White-throated Sparrows. Birds of the white-striped plumage morph refuelled better when food was provided, but stopover behaviour did not differ. Lastly, I used radar and acoustic recorders to test if birds were more likely to leave when other birds were passing by. Departure was not influenced the passage of migrants, but occurred earlier when wind conditions were more 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.

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