Northern Prairie Wildlife Research Center
Bureau of Land Management
Havre, Montana 59501
I made nest searches for three years, 1986-88. Two of the three years, 1986-87 were wet with most islands being surrounded by water, while 1988 was an extremely dry year and most islands were dry. Forty four (78%) and forty seven (84%) stock ponds contained at least one island that was surrounded by water in 1986 and 1987 respectively. Of these, 35 (79%) stock ponds contained at least one nest in 1986 and 42 (89%) contained at least one nest in 1987. A total of 99 (84%) islands in 1986 and 101 (86%) in 1987 were surrounded by water. Of these, 43 (43%) in 1986 and 57 (56%) 1987 contained nests. Nest success averaged 86% in 1986 and 91% in 1987. During the drought year of 1988 only 11 (20%) stock ponds contained islands that were surrounded by water. Of these, eight (73%) contained at least one island with a nest. Only 17 (14%) islands were surrounded by water in 1988. Nine (53%) of these contained nests with an average nest success of 78%. Brood size averaged 4.5 for all three years.
Moat shaped islands were also constructed in potholes twenty acres or larger which were dominated by western wheatgrass (Agropyron smithii). Use varied on these islands, averaging 11% during 1986 and 1987 and 70% during 1988. Nesting use was higher in 1988 due to the fact that these moat islands provided the only stable water source in the area.
Stock pond nesting islands are a relatively inexpensive way to provide a long term nesting substrate for Canada geese. Their life span is generally at least twenty years with almost immediate occupancy. Use and nest success are also high. Land management agencies as well as private landowners should be encouraged to construct nesting islands in existing stock ponds.