Environmental Factors that Influence Spring Migration Chronology of Lesser Scaup (Aythya affinis)
Dr. Scott Petrie, Long Point Waterfowl Executive Director
Dr. Michael Schummer, Long Point Waterfowl Scientist
Dr. Irena Creed, Western University
The combined continental population of lesser and greater scaup (Aythya marila) declined by approximately 50% between the mid-1980s and the late 1990s. These population trends highlighted the need for research targeting spring migration in scaup. By identifying if and how weather and environmental conditions during spring influence spring migration chronology we hoped to identify how weather influences timing and rate of migration whether or not current survey techniques were time to capture accurate estimates of the lesser scaup breeding population.
We used satellite telemetry to observe timing of spring migration of 78 adult female lesser scaup from 2005-2010, migrating west through the Prairie Pothole Region and east through the Great Lakes. Using weather data from the National Climatic Data Center, we observed how weather and environmental conditions during spring influenced migration chronology of lesser scaup at two spatial scales, a broad regional scale and a fine local movement scale. Also, using annual spring roadside migration surveys, we compared the arrival of lesser scaup and mallards into an area of North Dakota that is traditionally surveyed during spring by the spring breeding survey. This allowed for the comparison of timing of migration between mallards for which the spring breeding survey was designed and lesser scaup to help identify whether or not the survey may be producing inaccurate estimates of breeding scaup.
As hypothesized, several weather variables influenced scaup spring migration. At the regional spatial scale timing and rate of migration by scaup migrating through the prairies was influenced by temperature and precipitation. Analysis found that when conditions during spring were warmer and wetter migration occurred earlier and faster through the prairies. Following our prediction, in the Eastern route, weather that influences habitat availability had little effect on migration chronology or the timing of settling on breeding areas. With the invasion of Dreissenid mussels and increasing temperatures in the Great Lakes, diving waterfowl (including scaup) have access to an abundant year-round food source. In contrast to the Mid-continent, where wetland abundance and availability are influenced greatly by spring conditions, the Great Lakes and boreal wetlands are relatively less influenced by weather because of their greater size and permanency.
Observing migration and the influence of weather on a local movement scale, allowed for the detection of individual-specific conditions, thus identifying environmental factors that prompted migratory movements. Thawing Degree Days, a measure of temperature, which has been used as an index of vegetative growth, invertebrate hatch, and ice thaw was the primary cue scaup used to initiate migration. Thus, identifying scaup’s ability to ‘recognize’ suitable habitat conditions brought about by increasing temperatures and exploit newly available food resources.
The analysis of the North Dakota peak migration dataset did not detect any effect of weather on difference in timing of peak migration between scaup and mallard. However, it did suggest that scaup migrate at different times than mallards, and that the annual difference in the timing of scaup migration did not change consistently with that of mallards. Peak scaup migration into North Dakota typically occurred over a 14 day period in early to mid-April, whereas mallard migration peaked at the end of March and again late in May.
Our study identified the relative importance and influence of winter and spring weather on the migration chronology of satellite tracked scaup. Using a local movement analysis, we were only able to detect an influence of temperature on migratory movements, however because the analysis was limited to a smaller spatial scale, we were not able to detect the weather cues that drive migration at a regional scale. With the broad scale analysis measuring weather effects at a regional scale, we were able to detect the influence of temperature and precipitation on the timing and rate of migration. We detected the relative importance of habitat availability on spring migration by accounting for precipitation and ice cover effects. The North Dakota peak migration analysis, using count data to identify the difference in timing of peak migration between scaup and mallards, detected no substantial influence from weather factors. The results suggest that satellite telemetry data increase the ability to identify factors that influence migration chronology and provide more informed
predictive models of scaup spring migration. By providing some baseline information on how scaup react to weather and environmental variables, we are better able to understand spring migration patterns in scaup. Importantly, a better understanding of the timing and movements of scaup during spring is critical for interpreting population estimates, and for developing future management strategies.