FACTORS INFLUENCING BODY CONDITION AND ARRIVAL PHENOLOGY OF NEOTROPICAL MIGRANTS AT A NORTHERN SPRING STOPOVER SITE
González-Prieto, Ana María
Assessing the effect of winter habitat quality and environmental conditions on the fitness of migratory birds is important to understand factors that regulate migratory bird populations throughout the annual cycle. I evaluated the effect of winter habitat occupancy, as inferred from tissue stable carbon (δ13C) and nitrogen (δ15N) isotope values, on body condition and arrival date of seven long-distance, Nearctic-Neotropical migratory species intercepted during spring migration at Delta Marsh Bird Observatory (DMBO) southern Manitoba, Canada. Additionally, I used a long-term dataset of DMBO to assess the effect of May minimum temperature, May minimum daily temperature, and El Niño-Southern Oscillation (ENSO) index on body condition and spring arrival date. The effect of winter habitat quality on arrival day and condition index was strong for Palm Warbler (Sethophaga palmarum), Northern Waterthrush (Parkesia noveboracensis) and Alder Flycatcher (Empidonax alnorum). Palm Warblers using mesic winter habitats (i.e., low δ13C and δ15N values) were in better physical condition and arrived before individuals from more xeric habitats (with relatively higher δ13C and δ15N values). In Northern Waterthrush, early arrival was also related to mesic winter habitat occupancy. However, Alder Flycatcher showed an opposite trend. The effect of winter habitat on body condition and arrival phenology was more likely to be detected in species overwintering in the Caribbean. ENSO, probably through its influence on weather and food availability during winter, carried over to northern latitudes and affected both spring arrival date and condition. Condition was lower and birds arrived later during colder springs. Furthermore, I assessed whether brighter carotenoid-based first-winter plumage colouration conferred higher annual survivorship to yearling Yellow Warblers (Setophaga petechia) through the occupancy of higher-quality winter habitats. Hatch-year warblers were banded and plumage brightness scored from 2008 to 2010 at DMBO and a subset was recaptured as second-year adults the following spring. I used δ13C values derived from feathers and claws grown on the winter grounds to determine winter habitat occupancy of survivors. Independent of sex, I expected higher survivorship in brighter individuals and depleted δ13C values in winter grown tissues as an indicator of higher quality (e.g., mesic, higher food availability) winter habitat occupancy. Survival was higher in 2009 than in 2010; however, I did not find an effect of plumage brightness or sex on survival. Brighter colouration apparently did not confer survivorship advantages to males or female HY birds. Most individuals occupied xeric habitat during the winter independently of age, sex or plumage brightness. Further work on the winter grounds is needed in order to clarify the lack of power of winter habitat-occupancy to explain the arrival day and physical condition of most of the species on the breeding grounds, and survival in Yellow Warblers.
DegreeMaster of Science (M.Sc.)
SupervisorHobson, Keith A.
Copyright DateFebruary 2012