Reproductive Strategies Of Common Eiders (Somateria Mollissima)

Many reproductive strategies exist all with the same goal to maximize fitness. Because reproductive strategies affect fitness directly, there is interest to understand how they are utilized within a population. The two main strategies we focus on for this work related to Common Eiders (Somateria mollissima) are the utilization of conspecific brood parasitism as an alternative tactic beyond simply nesting and their ability to shift timing of breeding to align young with the best opportunity for survival. To accomplish studying our two reproductive strategies we monitored the Mast and WaWao Common Eider colonies located within Wapusk National Park, Manitoba. Our first aim was understanding conspecific brood parasitism or brood parasitism, which is the act of laying ones eggs (parasitizer) in the nest of another female (host), within the same species. Our objectives were to estimate the rate of brood parasitism using microsatellite loci, identify if non-random spatial and genetic distributions exist in our colonies, and if the relatedness between hosts and parasitizers are more related on average than females nesting in the general vicinity. We estimated the overall rate of brood parasitism to be 22.7% (176 of 775 offspring) with 50.7% (104 of 205 nests) of all nests containing at least one parasitic egg. We found a correlation between pairwise distance and relatedness, but it varied by year and colony. In addition, we did observe some cases of positive local autocorrelation between a focal female and her four nearest neighbors, but we observed negative local autocorrelation as well. Therefore, evidence of kin grouping is present, but not strong. The average pairwise relatedness of hosts and parasitizers, in 2016 (0.083), did not exceed the smallest spatial scale group’s average pairwise relatedness (0.152). However, average pairwise relatedness of host-parasitizer’s, in 2017 (0.308), was higher when compared to even the smallest spatial scale of 0-10 meters (-0.003). This indicates females potentially shift their preference to parasitize kin annually, which could be altered based on other environmental stressors. Our second aim was focused on the timing of breeding in Common Eiders, by understanding if weather affects the timing of breeding and if the timing of breeding was a predictor of breeding success. Our objectives were to identify weather related factors that affect timing of nest initiation and examine the effects spatial and temporal variables have on daily survival rate, one of which was date of nest initiation. We found Common Eiders date of nest initiation was correlated with the last day of snowmelt, but not other weather variables. However, date of nest initiation was not a predictor of daily survival rate in Common Eiders, but the day within the breeding season and the incubation stage of the female were, which we suggest could be consequences of the timing of predator arrival, in the colony. In addition, using estimates from our top model, we found it could be more beneficial to nest later in the season versus earlier, in certain years. However, the caveat of only using daily survival rate as an index of success was we have no estimate of post-hatch success indices (brood survival or recruitment), which may be impacted by timing differently.

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