Post-breeding movements of Swainson’s Thrush in Southern Nova Scotia
LE3 .A278 2018
Master of Science
Abstract for Chapter 1: Neotropical migrants are known to move over broad temporal and spatial scales during the post-breeding period. The extent of these movements has recently been investigated by Brown (2016) and Cormier (2017) in Blackpoll Warblers (Setophaga striata) on Bon Portage and Seal Island in Nova Scotia. Their studies revealed that, during this period, adults and hatch-years made regional-scale movements of over 200 km. Previous research has suggested that post-breeding movements are related to the selection of future nest sites. However, these have typically not included analyses at broad scales due to technological limitations. Miniaturization of radio transmitters as well as the development of automated radio telemetry has expanded opportunities to study this period in small migratory songbirds. I tracked post-breeding movements of Swainson’s Thrushes (Catharus ustulatus) using the same study area as in Brown (2016) and Cormier (2017) to allow for a comparison with a species that have similar overwintering are as (northern South America) but a different migratory route (Blackpoll Warbler; Setophaga striata). I found no evidence for 5 differences between ages in the number of sites visited or the tortuosity of movement. Hatch-years tended to slow down after departing their natal grounds and overall took longer to move towards their migratory destination when compared to adults. This supports the idea that hatch-years require more time than adults to reach their migratory destination, but there was only weak evidence that these timing differences were related to exploratory movements. Individuals from the more remote of the two islands (Seal Island) moved at a faster rate and had less tortuous movements than those from the less remote island (Bon Portage). This resultis consistent with the idea that individuals at more remote sites tend to choose more direct routes towards their migratory destination while those from sites closer to the mainland exhibit more regional exploration. Together these findings suggest exploratory movements may not be solely related to experience, but also to place of origin. Abstract for Chapter 2: Few studies have examined how nocturnal migrants behave in the days immediately prior to their first migratory flights. Cage studies suggest there is a hormonal shift that occurs in nocturnal migrants that causes individuals to become restless at night at a measurable rate prior to migration. Here, I examined the nocturnal flight behaviour of a wild Neotropical migrant, the Swainson’s Thrush, prior to departure from two island sites off coastal Nova Scotia, Canada: Bon Portage and Seal Island. I tested for differences between the behaviour of individuals depending on experience (age) and distance to the mainland (island) given that inexperienced birds require navigational cues to correctly orient themselves and mainland coastlines as well as polarized light at sunset as an aid. I show that compared to adults, hatch-years were far more likely to make pre-departure flights on the island and that hatch-years made flights closer to sunset at the more distant site (Seal Island) which supports the hypothesis that hatch-years require more cues than adults prior to initiating migration. Adults tended to depart closer to sunset than hatch-years and departed later in the season. Both adults and hatch-years from Seal Island departed closer to sunset than those on Bon Portage which suggests location plays a more significant role in determining departure time. Together, these findings suggest pre-departure flights are common in hatch-years prior to migration and that individuals at remote sites are more likely to make these flights when solar cues are available.
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