Study 1: Glucocorticoid response of captive great tits to mild, short term, changes in ambient temperature. This project addressed objective 1 and aimed to establish a RN in response to a change in temperature. We predicted that lower temperatures lead to increased baseline GC associated with increased metabolic rate in order to maintain body temperature. This project is one of the first attempts at applying a RN approach to GCs. Fifteen great tits (Parus major) were captured from a local forest and acclimatized to an indoor aviary. Next the birds were exposed to three different temperature regimes for three days each, e.g. cold, neutral, and warm. During the neutral treatment the normal temperature of the aviaries was used, e.g. 19C. The cold and warm treatment consisted of an average temperature of 14C and 24C, respectively. Birds were sampled once at prior to treatment, and again after 3 days of exposure to each treatment. Aside from plasma GCs, descriptive measures, such as weight, and behavior behavioral observations, were collected. This project is currently undergoing final data analysis and manuscript writing. Preliminary data was presented at the 2015 ICCPB conference in Krakau, Poland.
Study 2: Does individual GC flexibility predict reproductive success in free-roaming great tits? This project addressed objective 2, and aimed to assess individual GC responsiveness and HPA axis functioning in great tits in winter. We expected plasticity in baseline GC, e.g. a stronger response to temperature manipulation, to be positively related to reproductive success. Furthermore, we expected a more responsive HPA axis, e.g. strong stress response and robust negative feedback, to be associated with higher reproductive success. Prior to the breeding season, 24 animals were exposed to a temperature change and an HPA-function test. Great tits roost overnight in nest boxes in winter, providing an opportunity for relatively easy capture. Additionally, temperature inside a nest box can be manipulated relatively easily. Birds were caught at night, and assigned to either a control (10 animals), or a temperature manipulation group (14 animals). Upon capture, each bird was sampled to obtain baseline GCs. Temperature manipulation consisted of placing a heating pad in the bottom of the nest box, which was run off of a car battery. Birds were then returned to the box and left alone for three hours, after which each bird was recaptured and sampled again. Control birds were treated identical, except the heating pad was never turned on. After the second sample, birds were exposed to standardized stressor, containment in a cloth bag. After 30 minutes, a stress-induced sample was taken, immediately followed by a dexamethasone injection to induce negative feedback. A final sample was taken 90 minutes post injection. During the breeding season, 18 birds were found again actively building nests, and could thus be tracked to obtain measures of reproductive performance and success, including laying date, number of eggs, hatching success, feeding rate, and fledging success. This allowed us to investigate how winter GC flexibility is associated with reproductive success. This project is currently undergoing final data analysis and manuscript writing. Preliminary data was presented at the 2016 SICB conference in Portland, Oregon, USA.
Public outreach was an important aspect of this project. During the spring of 2015, a local high school biology class was guided around my experimental forest. This offered a great opportunity to interact with young students about research and to provide hands on experience on what it is like to be a field biologist. Additionally, some of the ideas and work described in this project were presented during seminars at Carleton University in Canada (February 2015), and Linkoping University in Sweden (October of 2015).
