I used band recovery data to test for the existence of a north-south gradient in survival and recovery rates for midcontinental populations of mallards (Anas platyrhynchos) during 3 time periods (1962-70, 1971-78, 1979-84). Mean annual survival rates for adult males and females were significantly associated with mean banding latitude (P < 0.0001 and P < 0.0004, respectively) and time period (P < 0.0001 and P < 0.001, respectively). Survival rates for both adult males and females were higher in the north and lower in the south. Because individuals from the northern regions migrate farther, the cost of migration in terms of survival was lower than some other factor(s) that may cause the gradient. The relationship between mean banding latitude and mean annual recovery rates was marginally significant for adult males (P = 0.043) but not for adult females (P = 0.183), suggesting that the gradient was not due to differential harvest pressure. At present, the north-south gradient in survival rates cannot be explained but may be caused by similar north-south clines in predation, habitat degradation, land use, and/or agricultural practices.
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North-south gradient in survival rates in midcontinental populations of mallards