Dr. Marjorie Sorensen

Postdoc (2018-present)

I study the factors that influence individual success with the long term goal of more accurately predicting the population dynamics of species, especially in response to environmental change. Much of my work integrates field observations with laboratory analyses (stable isotopes, plasma metabolites, stress hormone, intensity of malaria infection) to estimate physiological condition and past events experienced by individuals.

My research has examined the importance of seasonal interactions for the reproductive success of Pacific seabird species, the effects of rainfall on overwintering body condition of trans Saharan migratory songbirds, and the costs of malaria infection for migratory birds wintering in Africa. More recently, I have studied the factors influencing seed dispersal distances of plants. First, by examining the movements and seed dispersal patterns of Spotted Nutcrackers (Nucifraga caryocatactes) in alpine pine forests in Switzerland, and second, with disperser-based simulation models to estimate entire plant community seed dispersal distances. Understanding the factors determining dispersal distances is essential for predicting plant species distribution shifts in response to climate change and possible colonisation of new habitats.

At the University of Guelph, I will examine the effects of climate change on the population dynamics of Gray Jays (Perisoreus canadensis) in Algonquin Park. Evidence suggests that warming winter temperatures negatively affect Gray Jays by spoiling the cached food that is meant to sustain them over the winter months. I will be working to disentangle the effects of temperature and major thaw events on cached food quality and long-term population trends in Gray Jays.


Sorensen, MC, Fairhurst, GD, Jenni-Eiermann, S, Newton, J, Yohannes, E & Spottiswoode, CN. 2016. Seasonal rainfall at long-term migratory staging sites is associated with altered carry-over effects in a Palearctic-African migratory bird. BMC Ecology 16: 41. doi:10.1186/s12898-016-0096-6.

Sorensen, M.C., Jenni-Eiermann, S & Spottiswoode, CN. 2016. Why do migratory birds sing on their tropical wintering grounds? American Naturalist, doi: 10.1086/684681.

Sorensen, MC, Asghar, M, Bensch, S, Fairhurst, G, Jenni-Eiermann, S & Spottiswoode, CN. 2016. A rare study from the wintering grounds provides insight into the costs of malaria infection for migratory birds. Journal of Avian Biology 47: 001-008.

El-Arabany, N, Sorensen, MC & Hansson, B. 2015. Inferring the links between breeding and wintering grounds in a Palearctic–African migratory bird, the Great Reed Warbler, using mitochondrial DNA data. African Zoology 50: 241-248.

Carter, AJ, Horrocks, NPC, Huchard, E, Logan, CJ, Lukas, D, MacLeod, KJ, Marshall, HH, Peck, HL, Sanderson, JL & Sorensen, MC. 2014. Junior scientists are skeptical of sceptics of open access: a reply to Agrawal. Trends in Plant Science 19: 339-340.

Sorensen, MC. 2014. Singing in Africa: no evidence for a long supposed function of winter song in a migratory songbird. Behavioral Ecology 25: 909-915.

Sorensen, MC, Hipfner, JM, Kyser, TK & Norris, DR. 2010. Pre-breeding diet and ornament size in the Rhinoceros Auklet Cerorhinca monocerata. Ibis 152: 29-37.

Sorensen, MC, Hipfner, JM, Kyser, TK & Norris, DR. 2009. Carry-over effects in a Pacific seabird: stable isotope evidence that pre-breeding diet quality influences reproductive success. Journal of Animal Ecology 78: 460-467.

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