Henry R. Murkin

AVIAN HABITAT SELECTION AND PRAIRIE WETLAND DYNAMICS: A 10-YEAR EXPERIMENT

Northern prairie wetlands play a vital role in the life cycle of a wide array of bird species. Prairie wetlands used by birds span the entire range from shallow ephemeral ponds inundated for short periods each spring to large permanent water bodies that seldom, if ever, go dry. The objective of this study was to determine the response of blackbirds, waterfowl, and American Coots to changes in habitat structure induced by water level fluctuations in prairie wetlands. The study was conducted on a series of experimental marshes within the Delta Marsh in southern Manitoba, Canada. Water levels were adjusted following a predetermined schedule to simulate the wet–dry cycle of prairie marshes. Aerial photographs were taken annually, and habitats were characterized using Geographic Information System (GIS) techniques. Weekly avian censuses were related to habitat features using Principal Components Analysis (PCA) procedures. Yellow-headed Blackbirds selected shallowly flooded habitats with a mixture of open water...

A Comparison of Activity Traps and Sweep Nets for Sampling Nektonic Invertebrates in Wetlands

Activity traps were compared to sweep nets for sampling nektonic invertebrates in shallow freshwater wetlands using Kendall Rank Correlation. There was a significant correlation for total invertebrates. The presence of fish and invertebrate predators in the activity traps, water temperature, and water depth did not affect the significance of the correlation for total invertebrates. The correlations for the two functional groups considered, herbivore-detritivores and predator-parasites, were significant. The presence of fish in the activity trap did affect the correlations for some individual taxa. There were no correlations for several taxa of predaceous invertebrates. Considering its advantages and limitations, the activity trap can be useful in many types of experimental and long-term studies of nektonic invertebrates.

Relationships between waterfowl and macroinvertebrate densities in a northern prairie marsh

This study examined the relationships of waterfowl and American coot (Fulica americana) densities with macroinvertebrate levels in several diked ponds (cells) within the Delta Marsh, Manitoba. Following a year of normal water levels in 1980, the experimental cells were pumped to a depth of 1 m above normal for a period of 2 years (1981-82). Simple correlations between waterfowl and macroinvertebrate densities, coupled with behavioral observations, suggest that invertebrate densities may affect breeding waterfowl densities during springs with normal water depths. There were no significant correlations (P > 0.05) between waterfowl and macroinvertebrate densities during springs with above-normal water levels or during any of the fall periods. Coots showed no significant correlations (P > 0.05) with macroinvertebrate levels during any of the periods examined. This study suggests that future research on habitat selection by breeding waterfowl must address macroinvertebrates and/or factors affecting invertebrate distribution and abundance. J. WILDL. MANAGE. 50(2):212-217 Research on waterfowl habitat selection and food habits suggests that aquatic macroinvertebrates are important factors in determining avian use of marsh areas (McKnight and Low 1969, Schroeder 1973, Swanson and Meyer 1973, Kaminski and Prince 1981). While most research to date has focused primarily on the birds, further investigation into the habitats used by feeding birds is required. Murkin et al. (1982) showed that invertebrate levels may affect waterfowl use of manipulated cattail (Typha spp.) habitat during the spring breeding season. Their work, however, needs to be expanded to include other habitats and seasons of the year. Observations of behavior also should supplement bird counts to provide further evidence that invertebrate food resources affect marsh bird habitat selection (Swanson and Meyer 1973). The objective of the present study was to determine the influence of macroinvertebrate densities on waterfowl and coot use of northern prairie marsh habitat during the spring and fall. We thank B. D. J. Batt and A. G. van der Valk for review of the manuscript. Funding was provided by Ducks Unlimited Can. (DUC) and the North Am. Wildl. Found. through the Delta Waterfowl and Wetlands Res. Stn. (DWWRS). This is Pap. 9 of the Marsh Ecol. Res. Prog., a joint project of DUC and DWWRS. STUDY AREA AND METHODS The study was conducted on the experimental cells of the Marsh Ecology Research Program of the DWWRS and DUC (see Batt et al. [1983]). The cells are located on the Delta Marsh, a 20,000-ha lacustrine marsh on the southern shore of Lake Manitoba in southcentral Manitoba. Ten contiguous experimental cells (approx 6-ha each) were created by building a series of dikes along the northern edge of the marsh. Four of the 10 cells (1, 3, 7, and 8) were chosen randomly for a detailed examination of the invertebrate community (see Murkin [1983]). Each cell had independent water level regulation utilizing electric pumps. The schedule of water levels within the cells is shown in Table 1. Normal water levels are the naturally occurring levels of the Delta Marsh. Above-normal levels were planned to provide a depth of 1 m over the substrate of the existing cattail beds (Table 2). Invertebrate sampling stations were established according to a stratified random design within each of the 4 experimental cells, 2 sites within each of the following 5 cover types: open water (no emergent vegetation), common reed grass (Phragmites communis), whitetop rivergrass (Scholochloa festucacea), tule bulrush (Scirpus acutus), and cattail. To select sites a numbered grid (1-m intervals) was placed over

Decomposition of emergent macrophyte roots and rhizomes in a northern prairie marsh

Dry mass, nitrogen and phosphorus content in belowground litter of four emergent macrophytes (Typha glauca Godr., Phragmites australis (Cav.) Trin., Scolochloa festucacea (Willd.) Link and Scirpus lacustris L.) were followed for 1.2 years in a series of experimental marshes, Delta Marsh, Manitoba. Litter bags containing roots and rhizome materials of each species were buried in unflooded soil, or soil flooded at three water depths (1–30, 31–60, > 60 cm). There were few differences in dry mass loss in unflooded or flooded soils, and depth of flooding also had little effect on decomposition rates. In the flooded sites, Scolochloa and Phragmites roots lost more mass (48.9–63.8% and 59.2–85.5%, respectively) after 112 days than Typha and Scirpus (36.3–43.6 and 37.0–47.2%, respectively). These differences continued through to the end of the study, except in the shallow sites where Scirpus roots lost more mass and had comparable mass remaining as Scolochloa and Phragmites. In the unflooded sites, there was little difference between species. All litters lost nitrogen (22.9–90.0%) and phosphorus (46.3–92.7%) during the first 112 days, then levels tended to remain constant. Decay rates for our belowground root and rhizome litters were comparable to published literature values for aboveground shoot litter of the same species, except for Phragmites roots and rhizomes which decomposed at a faster rate (−k = 0.0014−0.0032) than shoots (−k = 0.0003−0.0007, [van der Valk, A.G., Rhymer, J.M., Murkin, H.R., 1991. Flooding and the decomposition of litter of four emergent plant species in a prairie wetland. Wetlands 11, 1–16]).

Flooding and the decomposition of litter of four emergent plant species in a prairie wetland

Changes in mass, N, and P for old and new litter of four emergent plant species (Scolochloa festucacea (Willdl.) Link,Phragmites australis (Cav.) Trin ex Steud.,Typha ×glauca Godr., andScirpus lacustris L. spp.glaucus (Sm.) Hartm.) were studied under two water-level regimes in a 10-cell experimental marsh complex in the Delta Marsh, Manitoba, Canada. In the normal regime, water levels were kept at the regulated water level for Lake Manitoba until the fall of 1981, while in the flooded or high-water regime, they were raised 1 m above the regulated level in the fall of 1980. In the spring of 1980, old litter (i.e., litter from the previous growing season) was placed in all ten cells of the complex, and in the fall of 1980, new litter (i.e., litter from the 1980 growing season) was placed in the same 10 cells. Litter ofS. festucacea had the highest mean decomposition rate (k=0.00171), followed byT. ×glauca (0.0131),S.l. glaucus (0.00126), andP. australis (0.00050). Mean decomposition rates were higher in the flooded treatment than in the normal treatment forP. australis andS. festucacea. Within water-level treatments, mass loss depended on initial litter age.The amount of N and P lost or gained by the end of 1981 varied with species, litter age, and water-level treatment.Scolochloa festucacea old and new litter had a lower percent N and P remaining in the flooded than in the normal water-level treatment. The percent N and P remaining in old litter ofP. australis andS.l. glaucus at the end of the study was higher than that in new litter regardless of water-level treatment. ForT. ×glauca, however, new litter had a higher percent of N and P remaining than old litter at the end of the study in both water-level treatments. Litter with lower initial N and P levels accumulated more N and P than did that with higher initial levels.

FACTORS AFFECTING SURVIVAL OF MALLARD DUCKLINGS IN SOUTHERN ONTARIO

Abstract Survival of young is poorly understood, but important to fitness and demographics for many birds. Estimates of duckling survival and the factors influencing it are essential to guiding regional breeding management for ducks. We estimated daily and 30-day duckling survival for Mallards (Anas platyrhynchos) at one of four sites each year during 1997–2000 in southern Ontario, Canada. We examined effects of site-year, brood age, female age, and hatching date on survival. Our best model supported additive effects of site-year, brood age, and hatching date. The odds of daily survival were 8.8 times (95% CI: 4.2–18.5) higher for older (>7 days) relative to younger (≤7 days) ducklings and 1.7 times (0.9–3.1) higher for early-hatched (before 1 June) relative to late-hatched (1 June or later) ducklings. When controlling for differences in hatching date, we did not find support for an influence of female age. Mean 30-day duckling survival across sites was 0.40 (range 0.07–0.50). Extremely low survival at one site appeared to be associated with poor wetland conditions. Our results suggested directional selection for early nesting, and we predicted that early nests made a disproportionately large contribution (61%) to recruitment to 30 days posthatching. We recommend management emphasis on protection, enhancement, and restoration of seasonal wetlands to prevent declines in duckling survival. Factores que Afectan la Supervivencia de Anas platyrhynchos en el Sur de Ontario Resumen. La supervivencia de los juveniles permanece poco entendida, aunque es importante para la adecuación biológica y la demografía de muchas aves. Las estimaciones de supervivencia de los juveniles de patos y los factores que la influencian son esenciales para guiar estrategias regionales de manejo reproductivo en patos. Estimamos la supervivencia diaria y a los 30 días de los juveniles de Anas platyrhynchos en un sitio por año para un total de cuatro sitios entre 1997–2000 en el sur de Ontario, Canadá. Estimamos los efectos de sitio-año, edad de la nidada, edad de la hembra y fecha de eclosión sobre la supervivencia. Nuestro mejor modelo respaldó efectos aditivos de sitio-año, edad de la nidada y fecha de eclosión. La supervivencia diaria fue 8.8 veces (95% IC: 4.2–18.5) mayor para juveniles de mayor edad (>7 días) en comparación con juveniles de menor edad (≤7 días) y 1.7 veces (0.9–3.1) mayor para juveniles que eclosionaron tempranamente (antes del 1 de Junio) en comparación con juveniles que eclosionaron tardíamente (durante o después del 1 de Junio). Cuando controlamos por diferencias en la fecha de eclosión, no encontramos evidencia de una influencia de la edad de la hembra. La supervivencia media, considerando todos los sitios, de los juveniles a los 30 días fue de 0.40 (rango 0.07–0.50). La supervivencia extremadamente baja que registramos en uno de los sitios parece estar asociada con las malas condiciones del humedal. Nuestros resultados sugirieron una selección direccional hacia la nidificación temprana, y predijimos que los nidos tempranos representaron una contribución desproporcionadamente grande (61%) al reclutamiento luego de 30 días de eclosión. Recomendamos que el manejo ponga énfasis en la protección, mejoramiento y restauración de humedales estacionales para prevenir una disminución en la supervivencia de los juveniles de patos.

Algal toxins—Initiators of avian botulism?

An outbreak of avian botulism in Whitewater Lake, Manitoba, Canada was associated with reducing sediments. But any linkage between sediments and botulism was only indirect; Clostridium botulinum was not observed in the sediments. The source of the C. botulinum was unclear but carcasses that overwintered appeared to perpetuate the outbreak. The algal toxins anatoxin‐a and microcystin‐LR were present (17≤mg/L) when many birds were moulting and unable to fly, likely making them more sensitive to botulism. The sediment anoxia released phosphorus into lakewater so that concentrations increased from about 73 to 470 mg/L and enhanced growth of Microcystis and Aphanizomenon. Wind resuspension of sediments resulted in areas with more algal biomass and associated algal toxins. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 558–567, 2000

Nektonic invertebrate abundance and distribution at the emergent vegetation-open water interface in the Delta Marsh, Manitoba, Canada

The emergent vegetation-open water interface plays an important role in the use of freshwater wetlands by many species of animals. The objective of this study was to monitor the distribution and abundance of free-swimming invertebrates at the cattail (Typha × glauca Godr.)—open water interface in two bays (sheltered and unsheltered) in the Delta Marsh in south-central Manitoba during 1985. Submersed vegetation densities were higher in the open water sites of the sheltered bay during most of the summer. Water temperatures were constant across the interface through much of the year. By mid-summer, hypoxic conditions prevailed within the water column in the cattail stand. Algae levels were similar across the interface throughout much of the year, with peaks occurring just inside the interface in June and July. Early in the season, there was a trend for higher nektonic invertebrate numbers within the cattail stands of both bays. By late August, there were similar total invertebrate numbers across the interface. Cladocera and ostracod numbers were higher within the cattail stands during June and July; during the same periods, corixid levels were higher in the open water sites. The low oxygen levels within the cattail stands during the summar may reduce predation by fish and other predators that cannot tolerate low oxygen levels. This may explain the higher numbers of prey species like cladocerans and ostracods within the cattail stands during mid-summer. The presence of algal or detrital food resources seemed to have little influence on invertebrate abundance across the interface during this study. Peaks in invertebrate abundance did not occur at the emergent vegetation-open water interface during any of the sampling periods in this study. The high invertebrate diversity and abundance in interspersed wetland habitat may be related more to the mixture of habitat types rather than the amount of interface present.

Population Dynamics of Mallards Breeding in Agricultural Environments in Eastern Canada

Abstract Population dynamics of mallards (Anas platyrhynchos) in eastern North America likely differ relative to the midcontinent population, but independent management has been hampered by lack of data. We used data from radiomarked females from 4 sites in southern Ontario and 1 site in New Brunswick during 1992–2000 to assess demographic performance during the breeding season and to inform regional management strategies. For each site, we estimated recruitment of female young to 30 days posthatch per breeding female and projected the finite rate of population growth λ, assuming annual survival typical of the region. We constructed a matrix population model for females and conducted perturbation analyses (i.e., analytic sensitivities and elasticities) to predict response of λ to change in vital rates. Excluding 1 site, we estimated mean recruitment of 0.89 (range = 0.79–0.98). At 1 site, duckling survival approaching zero resulted in extremely low estimated recruitment (0.08). Perturbation analyses indicated that λ was highly sensitive to changes in nest survival and nonbreeding survival and moderately sensitive to changes in survival of breeding females. Recruitment for most of our sites was >2 times the mean for the Prairie Pothole Region of Canada and likely was sufficient to maintain populations despite relatively high hunting kill in the region. Despite high sensitivity of λ to nest survival, intensive management to increase nest survival likely would be inefficient because of uniform nest survival among habitats and low nest densities. Because recruitment levels were generally high but densities of breeding pairs low, we recommend protection, enhancement, and restoration of wetlands to maintain and increase habitat suitability for breeding mallards as likely the most cost-efficient management strategy to benefit populations. Relatively high hunting kill and high sensitivity of λ to nonbreeding survival imply that harvest is important to regional population dynamics and suggest the potential effectiveness of adaptive harvest management.

Wetland plant responses to varying degrees of purple loosestrife removal in southeastern Ontario, Canada

This study examined the response of native vegetation to varying levels of purple loosestrife (Lythrum salicaria) removal and determined its impact on subsequent loosestrife germination and establishment in a southern Ontario wetland during 1993 and 1994. The study site was treated in 1991 with varying dosages of triclopyr amine herbicide, the triethylamine salt formulation of triclopyr [[(3,4,6-trichloro-2-pyridinyl)oxy] acetic acid]; 4.0, 8.0, and 12.0 kg active ingredient (a.i.)/ha. Different levels of adult loosestrife control were achieved. The lowest density of adult loosestrife was observed in the 8.0 and 12.0 kg a.i./ha treatment plots where root kill was most effective. Most new adult loosestrife plants in the 8.0 and 12.0 kg a.i./ha treatment plots established from seed. The highest densities of loosestrife seedlings and grass (Gramineae) species were observed in the treatment plots with the lowest number of adult loosestrife plants (12.0 kg a.i./ha). Sedge species (Carex spp.) did not differ between treatment levels during 1993 and 1994. Loosestrife seedling densities decreased from 1993 to 1994, suggesting that increased native plant species can slow the rate of loosestrife reestablishment from the seed bank. Native vegetation seems to replace adult loosestrife for a limited time following herbicide application; however, without subsequent treatment, loosestrife will slowly reinvade a wetland.