| Abstract: | Accurate determination of age is of fundamental importance to population and life history studies of waterfowl and their management. Therefore, we developed quantitative methods that separate adult and immature blue-winged teal (Anas discors), cinnamon teal (A. cyanoptera), and northern shovelers (A. clypeata) during spring and summer. To assess suitability of discriminant models using 9 remigial measurements, we compared model performance (% agreement between predicted age and age assigned to birds on the basis of definitive cloacal or rectral feather characteristics) in different flyways (Mississippi and Pacific) and between years (1990-91 and 1991-92). We also applied age-classification models to wings obtained from U.S. Fish and Wildlife Service harvest surveys in the Mississippi and Central-Pacific flyways (wing-bees) for which age had been determined using qualitative characteristics (i.e., remigial markings, shape, or wear). Except for male northern shovelers, models correctly aged lt 90% (range 70-86%) of blue-winged ducks. Model performance varied among species and differed between sexes and years. Proportions of individuals that were correctly aged were greater for males (range 63-86%) than females (range 39-69%). Models for northern shovelers performed better in flyway comparisons within year (1991-92, La. model applied to Calif. birds, and Calif. model applied to La. birds: 90 and 94% for M, and 89 and 76% for F, respectively) than in annual comparisons within the Mississippi Flyway (1991-92 model applied to 1990-91 data: 79% for M, 50% for F). Exclusion of measurements that varied by flyway or year did not improve model performance. Quantitative methods appear to be of limited value for age separation of female blue-winged ducks. Close agreement between predicted age and age assigned to wings from the wing-bees suggests that qualitative and quantitative methods may be equally accurate for age separation of male blue-winged ducks. We interpret annual and flyway differences in remigial measurements and reduced performance of age classification models as evidence of high variability in size of blue-winged ducks‘ remiges. Variability in remigial size of these and other small-bodied waterfowl may be related to nutrition during molt. |
| Genre: | Article |
| ProdID: | 5223403 |
| Citation Author: | Hohman, W.L.; Moore, J.L.; Twedt, D.J.; Mensik, J.G.; Logerwell, E. |
| Citation Contributing Office: | Patuxent Wildlife Research Center |
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| Citation End Page: | 735 |
| Citation Issue: | 4 |
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| Citation Language: | English |
| Citation Larger Work Title: | Journal of Wildlife Management |
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| Citation Number Of Pages: | 9 |
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| Citation Phsyical Description: | 727-735 |
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| Citation Search Results Text: | Age-class separation of blue-winged ducks; 1995; Article; Journal; Journal of Wildlife Management; Hohman, W.L.; Moore, J.L.; Twedt, D.J.; Mensik, J.G.; Logerwell, E. |
| Citation Start Page: | 727 |
| Citation Volume: | 59 |
| Citation Year: | 1995 |
| Type: | citation/reference |
| Text: | Age-class separation of blue-winged ducks; 1995; Article; Journal; Journal of Wildlife Management; Hohman, W.L.; Moore, J.L.; Twedt, D.J.; Mensik, J.G.; Logerwell, E. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DOCUMENT): | http://www.jstor.org/stable/3801949 |
| Date Other: | Wed, 16 Jun 2010 12:17 -0500 |
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