1. The need to get the basics right in wildlife field studies;Anderson;Wildlife Society Bulletin,2001
2. Ecology of spring-migrating Anatidae: a review;Arzel;Journal of Ornithology,2006
3. Evaluation of air/ground count comparisons for wintering American black ducks;Heusmann;Wildlife Society Bulletin,1990
4. Wildfowl counts in Denmark in November 1967 and January 1968-methods and results;Joensen;Danish Review of Game Biology,1968