The Influence of Energetic Condition on Flight Initiation and Orientation of Migratory Passerines in the Gulf of Maine Region

Covino, Kristen

ABSTRACT 'Energetic condition influences migratory decisions made by songbirds. Over-water or coastal flights are often the shortest routes but may be dangerous for landbirds because they may get caught over water where they are not able to rest and refuel. In this study, I performed trials on migratory songbirds in the Gulf of Maine region to investigate how various components of energetic condition relate to the likelihood that an individual will initiate migratory flight and the direction that it will choose with respect to the local topography of the stopover site. I used release tests and measurements of energy stores (fat), indicators of fattening trajectory (plasma triglycerides), and within day changes in body mass to investigate whether any of these measures of condition were related to the decisions migrants must make about when and where to go. My results indicate that the amount of fat a bird has at the time of release influences the decision to initiate a flight as well as directional decisions once a bird has decided to initiate migration. Both plasma triglyceride levels and within-day changes in body mass were higher in birds that initiated migratory flights; however, neither was directly related to directional decisions. Based on these results, it appears that migrant songbirds on stopover rely on cues about their energetic condition when making departure and orientation decisions but that the cues for making departure decisions are not always used for deciding where to fly.' /STUDY LOCATIONS:/ /SCHOODIC PENINSULA/