Climate trends, weather fluctuations and calving phenology in Svalbard reindeer (Rangifer tarandus platyrhynchus)
Master thesis by Preben Danielsen
Reproduction is known to be one of the most energetically demanding processes in the life of an organism, and in seasonal environments, vertebrate offspring production is therefore timed to coincide with the annual peak in resource availability. However, the recent advancement of spring phenology due to increased global temperatures may lead to a mismatch between peak resource availability and the high-energy requirements of reproduction. For high Arctic herbivores, such as reindeer, the onset of spring represents the start of a short time window of high resource availability crucial for development and survival, and a trophic mismatch may potentially influence reproductive success. As initiation of reproduction is often determined by cues distant in time of the annual peak in resources, one important question is therefore whether herbivores are able to match the recent advancement of plant phenology. Using data describing the timing of calving in Svalbard reindeer over a time period of 37 years, I here document the lack of changes in calving phenology in this species, despite significant advancement in the onset of spring during the same period. This suggests that the potential development of a trophic mismatch may already be happening, or will happen, but the future consequences are more difficult to predict. Also, my results indicate that the Svalbard reindeer display a certain degree of response in their calving phenology in relation to annual weather fluctuations. My findings suggest that an earlier onset of spring seemed advance calving date when the preceding winter conditions had been severe, whereas this effect was not found when the preceding winters conditions were milder. This interaction effect is possibly due to icing events which decrease forage accessibility in winter, and in turn, reduce body condition of parturient females. Even so, results should be interpreted cautiously due to low sample size and potential confounding factors. Therefore, in future studies, more comprehensive data is needed to adequately address questions about the influential mechanisms on phenology.
Institute of Biology, Department of Natural Sciences, NTNU