WSI Description

Using different combinations of temperature and snow depth data available on the Internet and waterfowl counts from Wildlife Areas and Refuges, Schummer et al. (2010) determined that the cumulative affects of temperature and snow over several days influenced mallard migration from northern and mid-latitudes towards their southern wintering grounds. One cold evening may not force large numbers of mallards to migrate, but consecutive days below freezing makes it difficult for even a large duck like a mallard to maintain body fat. Fat is a key component for fall and winter survival , but when ducks are subjected to below freezing temperatures they burn fat to maintain core body temperature (which is ~104◦F) and often opt to head south warmer regions. Other factors also influence migration, such as snow and ice cover that reduces the functional availability of foods that mallards eat in wetlands and crop fields. Overall, the combined effects of several consecutive days of below freezing temperaturs and snow cover best explain mallard migration out of northern and mid-latitude staging areas. To calculate the mallard WSI, someone only needs the current daily mean temperature (in degrees Celsius), and snow cover (in inches). When the WSI increases, so does the likelihood that mallards will leave northern and mid-latidues for areas to the south.

To calculate the WSI
1/ use the daily mean temperature and switch the sign. For example, -5◦C would be given a value of 5 and +5◦C would be given a value of -5
2/ count up the consecutive days when the mean daily temperature was below zero, if two days in a row were below freezing your value would be 2
3/ determine the snow depth in inches, if there is 5 inches of snow on the ground your value would be 5
4/ determine the number of consecutive day when there was measurable snow on the ground, if the 5 inches of snow had been on the ground for 3 days, your value would be 3
5/ add the numbers from 1 through 4 above, this is your WSI value. When the WSI value is 7.2 or greater there is increased likelihood of decreasing mallard abundance between two days at your location.


A list of related work out of Mississippi State University.

Schummer et al. 2010: Weather-Related Indices of Autumn - Winter Dabbling Duck Abundance in Middle North America

Estimating Effects of Climate Change on Autumn-winter Distributions of Dabbling Ducks in Eastern North America

Predicting Duck Migration with a Weather-Severity Index

Data Used

For information about the North American Regional Reanalysis (NARR) please visit National Oceanic & Atmospheric Administration

For more information about the Network Common Data Form (NetCDF) please visit Unidata

All of the WSI values shown in this web application as well as the WSI calculations available in NetCDF format were created using Python and NARR data.
The maps scenes were all generated using Python for ArcGIS.

Upper Midwest and Great Lakes Landscape Conservation Cooperative Long Point Waterfowl Ducks Unlimited Mississippi State

In using this open-access WSI web application to obtain data you agree to cite any work derived thereafter using these data as

Mitchell, M., M. L. Schummer, J. Coluccy, R. Macleod. 2014. An open-access web-based tool for querying weather severity index data used to predict mallard migration in the Central, Mississippi, and Atlantic Flyways, September - March 1979 - 2012. Accessed online: