David P. Rave

Relationships of habitat patch size to predator community and survival of duck nests

We studied duck nest success and predator community composition in relation to size of discrete patches of nesting cover in the Prairie Pothole Region (PPR) of the United States in 1993-95 We focused on nests in uplands that were seeded to perennial grasses and forbs and enrolled in the Conservation Reserve Program (CRP) in Minnesota, North Dakota, and South Dakota. We estimated daily survival rates (DSRs) of upland duck nests and indices of activity for red foxes (Vulpes vulpes), coyotes (Canis latrans), American badgers (Taxidea taxus), striped skunks (Mephitis mephitis) and Franklins ground squirrels (Spermophilus franklinii) and related these variables to habitat patch size. The effect of patch size (small vs. large) on estimated annual mean DSR was dependent on date of nest initiation (early vs. late) and year. Examination of within-year comparisons for early and late nests suggested that DSR was generally greater in larger habitat patches Activity indices for the 5 mammalian nest predators were influenced differently by year, location, and patch size. Activity indices of the red fox were greatest in small patches. Coyote indices were the most inconsistent, demonstrating a year × location × patch size interaction. Activity indices of the striped skunk and American badger varied only among years. Franklins ground squirrel indices were affected by study area location, with higher indices in the southeast than the northwest. Red fox activity was weakly correlated with that of the striped skunk and coyote. Although a positive relationship between habitat patch size and nest success probably exists, we believe the experiment to fully test this hypothesis will continue to be elusive.

Factors influencing incubation egg-mass loss for three species of waterfowl

Abstract Many bird eggs lose ∼15% of their fresh mass before pipping, but individual species have been reported to lose 10–23%. Most published estimates have been imprecise due to small sample sizes. Moreover, published estimates of within- or among-species variance components of mass loss are virtually unknown. We modeled the influence of nest type, clutch size, and egg size on daily mass loss of Mallard (Anas platyrhynchos), Common Goldeneye (Bucephala clangula), and Hooded Merganser (Lophodytes cucullatus) eggs and compared fractional mass loss among species. Mallard eggs in artificial nest cylinders lost more mass than those in ground nests, but were unaffected by nest initiation date. Average-sized eggs in Mallard ground nests, Mallard cylinder nests, and Common Goldeneye and Hooded Merganser nest boxes lost 7.9 g (15.2%), 10.8 g (20.3%), 10.3 g (15.5%), and 9.2 g (15.8%) of fresh mass, respectively. For all species, daily mass loss increased as incubation progressed and was affected by an interaction between egg size and incubation time, but was not influenced by clutch size. Depending on species, smallest eggs lost 1.0–4.0% more of their fresh mass than did the largest. Egg-mass variability was partitioned into years, nests within years, and eggs within nests and years. Variability was evenly distributed among the variance components in Mallard ground nests; however, among-eggs within-nest variance predominated in nest cylinders. In contrast, among-nests variation was the dominant source for goldeneyes and mergansers. Nest-site selection and egg size likely involve trade-offs among optimum egg-mass loss and nest and hatchling survival. Factores que Influencian la Pérdida de Peso de los Huevos durante la Incubación en Tres Especies de Aves Acuáticas Resumen. Muchas aves pierden aproximadamente el 15% de su peso fresco antes de iniciar la ruptura del cascarón, pero se ha reportado que esto varía entre especies entre el 10 y el 23%. La mayoría de los estimados publicados han sido imprecisos debido a tamaños de muestra pequeños. Más aún, los estimados de los componentes de la varianza dentro de especies o entre especies en la pérdida de peso son virtualmente desconocidos. En este estudio modelamos la influencia del tipo de nido, el tamaño de la nidada y tamaño del huevo sobre la pérdida diaria de peso en huevos de Anas platyrhynchos, Bucephala clangula y Lophodytes cucullatus, y comparamos la fracción de peso perdida entre especies. Los huevos de A. platyrhynchos perdieron más peso en nidos cilíndricos artificiales que en nidos en el suelo, pero no fueron afectados por la fecha de iniciación de la nidificación. Huevos de tamaño promedio de A. platyrhynchos puestos en nidos en el suelo y en cilindros, y huevos de B. clangula y L. cucullatus puestos en cajas de nidificación, perdieron 7.9 g (15.2%), 10.8 g (20.3%), 10.3 g (15.5%) y 9.2 g (15.8%) de su peso fresco, respectivamente. Para todas las especies, la pérdida diaria de peso se incrementó a medida que progresó la incubación y fue influenciada por una interacción entre el tamaño de los huevos y el tiempo de incubación, pero no por el tamaño de la nidada. Dependiendo de la especie, los huevos más pequeños perdieron entre 1.0 y 4.0% más de su peso fresco que los huevos más grandes. La variabilidad en el peso de los huevos estuvo repartida entre años, entre nidos de un mismo año y entre huevos de un mismo nido en cada año. La variabilidad estuvo igualmente distribuida entre sus distintos componentes en los nidos de A. platyrhynchos del suelo. Sin embargo, la varianza entre huevos de un nido predominó en los nidos puestos en cilindros. En contraste, la variación entre nidos fue la más importante en B. clangula y L. cucullatus. La selección de sitios de nidificación y el tamaño de los huevos probablemente involucran una solución de compromiso entre los niveles óptimos de pérdida de peso de los huevos y de supervivencia de los nidos y pichones.

DOES MALLARD CLUTCH SIZE VARY WITH LANDSCAPE COMPOSITION: A DIFFERENT VIEW

Abstract We report on the relationship between Mallard (Anas platyrhynchos) clutch size and cropland area in the landscape in western Minnesota during 1997–1999. We measured clutch size in two types of nest structures and fit a mixed-effects model to the data to examine the relationship. Our model also included covariates to control for the effects of year, nest initiation date, estimated pair numbers, and nest structure type. Unique landscapes associated with each nest (n = 134) ranged from 46.4–84.8% cropland. Clutch size was unrelated to cropland area, nest structure type, and estimated number of pairs with access to structures. Mean clutch size declined with nest initiation date early in the nesting season, but increased somewhat for nests initiated after 30 May. Clutch size also differed among years. Mean clutch size, adjusted for nest initiation date, was 11.0 ± 0.19 SE for 1997, 10.5 ± 0.19 SE for 1998, and 11.0 ± 0.19 SE for 1999. Conclusions regarding the significance of the year effect and the degree of nonlinearity due to nest initiation date were sensitive to potential clutch size outliers, but cropland area had no effect on clutch size regardless of the way we constrained clutch size. Nest parasitism by philopatric females laying in certain structures might explain the observed increase in clutch size in late nest initiations.

Cost and Precision Functions for Aerial Quadrat Surveys: a Case Study of Ring-Necked Ducks in Minnesota

Abstract Cost considerations may be as important as precision when making survey-design choices, and the ability to accurately estimate survey costs will be essential if survey budgets become more constrained. We used data from a survey of ring-necked ducks (Aythya collaris) to illustrate how simple distance formulas can be used to construct a cost function for aerial quadrat surveys. Our cost function provided reasonable estimates of effort (hr) and costs, and allowed us to evaluate plot-size choices in terms of expected cost-precision tradeoffs. Although factors influencing costs in wildlife surveys can be complicated, we believe that cost functions deserve more attention and should be routinely considered in conjunction with traditional power analyses.

Influence of Land Use on Mallard Nest-Structure Occupancy

Abstract We investigated the relationship between land use and mallard (Anas platyrhynchos) occupancy of single- and double-cylinder nest structures on a 658-km2 (254-mile2) western Minnesota, USA, study area from 1997–1999. We used hierarchical logistic regression to spatio-temporally model structure occupancy as a function of land use, number of nearby structures, number of mallard pairs with access to the structure, size of the open-water area including the structure, and structure type. We fit models to data from 4 different-sized buffers around each structure to investigate scale influences. Goodness-of-fit, predictive ability, and amount of reduced spatio-temporal correlation were similar for each buffer-size model. We made inferences using the 1.6-km-radius buffer model because it produced the lowest deviance. The amount and attractiveness of nesting cover (i.e., as indexed by visual obstruction measurements [VOMs]) within a buffer interacted with nest-initiation period (P = 0.003). The VOMs and nest occupancy were positively associated early in the nesting season, but the pattern reversed later in the nesting season. Structure occupancy and area of open water around a structure were related quadratically (P = 0.004), with odds of a structure in median-sized open-water areas being occupied increasing until the open-water area was ~16 ha. Year and nesting-season period interacted (P = 0.002), reflecting different nest-initiation phenology. Number of pairs with access to a structure had no effect on nest initiations (P = 0.7), perhaps due to our inability to account for within-season changes in pair numbers. Number of nearby structures (P = 0.8) was unrelated to initiation probability, but structure density was low (0.05/km2). We suspect that mallard settling patterns and an unmeasured temporal relationship between VOMs and numbers of pairs with access to structures produced the VOM × period interaction. Structures deployed in larger open-water areas where surrounding residual upland cover is abundant can improve mallard nest success early in the nesting season when duckling survival is the greatest and can reduce hen mortality associated with nest destruction and re-nesting.

Cost‐Effectiveness of Single‐ Versus Double‐Cylinder Over‐Water Nest Structures

Abstract Minnesota waterfowl management plans prescribe widespread deployment of mallard (Anas platyrhynchos) nest structures. We compared 53 single- and 57 double-cylinder nest structures from 1996 to 2003 because managers used both structure types but were uncertain about their respective cost-effectiveness. More nests occurred in double-cylinder structures, but numbers of successful nests and hatched ducklings were comparable for both types. Nest success in single- and double-cylinder structures was 92.8% and 79.4%, respectively, with nest abandonment being >4.5 times greater in doubles. Structure damage occurred only at ice-out and was greater for doubles. However, relative risk of failure for double- versus single-cylinder structures was similar (1.26; 95% CI = 0.91–1.75) and increased with size of the open-water area containing the structure. Modeling indicated approximately 95% of recruits from nest structures were additional recruits. A case-history approach indicated doubles produced an additional recruit for

Activity Budget of Green-Winged Teal Wintering in Coastal Wetlands of Louisiana

23.11 versus

DIURNAL TIME-ACTIVITY BUDGETS OF WINTERING CANVASBACKS IN LOUISIANA

23.25 for singles. However, these estimates were sensitive to assumptions used to apportion costs between structure types and ignored structure-placement influences. Placement affected cost-effectiveness significantly, with structures placed in open-water areas >10 ha being more cost-effective. Results also suggested singles might be more effective than doubles when placement is considered. Lower nest abandonment alone might make single-cylinder structures the better choice.