Daniel G. McAuley

THE ROLE OF pH IN STRUCTURING COMMUNITIES OF MAINE WETLAND MACROPHYTES AND CHIRONOMID LARVAE (DIPTERA)

Aquatic vascular plants, or macrophytes, are an important habitat component for many wetland organisms, and larvae of chironomid midges are ubiquitous components of wetland fauna. Many chironomids are primary consumers of algae and detritus and form an essential energetic link between allochthonous and autochthonous primary production and higher trophic levels, while others are predators and feed on smaller invertebrates. Live macrophytes serve mostly as habitat, whereas plant detritus serves as both habitat and as a food source. Assemblages of macrophytes and chrinomid larvae were surveyed in ten Maine wetlands, five with low pH (<5.0) and five with high pH (>5.5), and explained in terms of physical and chemical habitat variables. Macrophyte richness was significantly greater, and richness of chironomid larvae was lower, in low pH wetlands. There was no difference in chironomid abundance related to pH. However, community structure was related to pH, suggesting that competitive dominance of a few taxa was responsible for lower richness in low pH wetlands, whereas competition was weaker in high pH wetlands, making coexistence of more chironomid taxa possible. An examination of individual chironomid taxa by stepwise multiple regression showed that distribution of most taxa was controlled by water chemistry variables and macrophyte habit (i.e., floating, submergent).

Survival of American Black Ducks radiomarked in Quebec, Nova Scotia and Vermont

We monitored survival of 397 radiomarked juvenile American black ducks (Anas rubripes) distributed among Les Escoumins (n = 75) and Kamouraska, Quebec (n = 84). Amherst Point, Nova Scotia (n = 89), and a site on the Vermont-Queber border (n = 149) during autumn 1990 and 1991. Eighty-six percent (215 of 250) of all confirmed mortalities during the study was from hunting: 72% of marked ducks were shot and retrieved and 14% were shot and unretrieved. We tested for differences in survival in relation to sex, body mass, year (1990-91, 1991-92), and among the 4 locations for each of 2 monitoring periods (early, EMP: late. LMP). With data from the EMP for Vermont-Quebec in 1990 and 1991, Les Escoumins in 1990, and Amherst Point in 1991, survival of hatching-year (HY) males and females did not differ (P = 0.357). For sexes combined for the EMP, survival of ducks was greater in 1991 than 1990 (P = 0.086), and differed among locations (P = 0.013). Survival (years combined was greater al Amherst Point than at Kamouraska (P = 0.003) and Vermont Quebec (P = 0.002) during the EMP. The highest survival rate at Amherst Point (0.545 ± 0.056 [SE]) was associated with the latest date (S Oct) of season opening: the lowest survival rate (0.395 ± 0.043) was at the Vermont-Quebec border, where hunter numbers and activity were greatest. For the LMP. no interaction between years and locations was detected (P = 0.942), and no differences in survival existed between vears (P = 0.102) and among locations (P = 0.349). No association was detected between body mass at capture and survival of combined males and females during the EMP (P = 0.572) or during the LMP (P = 0.965). When we censored hunting losses for combined years for each period. EMP or LMP, all survival estimates exceeded 0.800 (0.809-0.965). These data emphasize need for an improved harvest strategy for American black ducks in North America to allow for increases in breeding populations to achieve population goals.

Survival of postfledging female American black ducks

We equipped 106 hatching-year (HY), female, black ducks (Anas rubripes) with transmitters during 1985-87 and monitored survival from late August to mid-December on a lightly hunted area on the Maine-New Brunswick border. The 1985-87 estimate of survival (hunting losses included) was 0.593, and when losses from hunting were censored it was 0.694. Survival in August-September was 0.987; by 31 October survival declined to 0.885, and by 30 November it was 0.718. Most nonhunting mortality was caused by predators (21/41, 53.2%); there were 14 deaths (34.1%) from mammals or unknown predators and 7 (17.1%) from raptors. Hunting caused 13 (31.7%) deaths. Ducks with lowest mass had the lowest survival. The estimate of survival for postfledging female black ducks, when multiplied with interval survival rates for hunting, winter, and breeding periods, produced an annual survival estimate of 0.262, about 12% lower than that (0.38) based on analysis of banding data

Foods of juvenile ring-necked ducks: Relationship to wetland pH

Foods of 37 juvenile ring-necked ducks (Aythya collaris) from 16 different wetlands were examined in eastcentral Maine in 1983-85. Invertebrates made up 70% aggregate dry weight (100% occurrence) of the foods of Class Ia-IIa (-24 days old) ducklings and 32% (86% occurrence) of Class IIb-III (>25 days old) ducklings. These percentages may be as high as 85% for Ia-IIa ducklings and 47% for IIb-III ducklings after adjusting for insect sclerites. Ducklings ate invertebrates from 44 taxa and seeds or fibers from 23 plant taxa. Freshwater sponges (Porifera) were the most important invertebrate and constituted 23% of the foods of all ducklings. Seeds of pondweeds (Potamogeton spp.) were the most important plant foods. Diets of ducklings from high-pH (26.1) wetlands were more diverse (t = 2.54, P = 0.021) than those from low-pH (<6.1) wetlands and consisted of 33 invertebrate taxa. Only 17 taxa occurred in ducklings from low-pH ponds. Class Ia-IIa ducklings from high-pH wetlands ate more invertebrates (77%) than ducklings from lower-pH wetlands (61%), although the difference was not significant (P = 0.21). Sponges made up the largest percentage of the diets and occurred in similar amounts in high(34%) and low(31.5%) pH wetlands. J. WILDL. MANAGE. 52(2):177-185 Aquatic invertebrates are important foods for young ducklings (Bartonek and Hickey 1969, Sugden 1973, Reinecke 1979), and retarded growth and low survival have been associated with low invertebrate abundance (Street 1977). Aquatic invertebrates are important in the diet of ring-necked duck ducklings in Minnesota (Hohman 1985). Mendall (1958) reported the foods eaten by ring-necked ducks in Maine, but his data included only gizzard contents, which bias results toward the less digestible plant foods (Swanson and Bartonek 1970). Ring-necked duck habitats in Maine consist primarily of permanent wetlands that have lower productivities than newly-flooded or seasonally-flooded wetlands (Whitman 1974). Many wetlands in Maine are vulnerable to acidification, a process that can adversely affect invertebrates (Bell 1971, Haines 1981, Eilers et al. 1984). Reinecke (1977) reported no difference in the nutrient content of duck foods in Maine wetlands versus richer, prairie wetlands, and he believed that food quantity rather than quality limited waterfowl in the Northeast. Low invertebrate diversity or biomass in wetlands could adversely affect duckling diets. The purpose of our study was to document food habits of ring-necked duck ducklings in Maine and to determine if diets differed between wetlands of high and low pH. We thank A. G. LaRochelle, P. E. Malicky, D. D. Eggeman, and R. R. Roy for their assistance in the field. T. M. Mingo identified invertebrates and J. E. Longcore identified sponges. K. L. Stromborg analyzed water samples. M. A. Howe, K. J. Reinecke, T. W. Custer, and 2 anonymous referees gave helpful reviews of the manuscript. STUDY AREA AND METHODS Our study area consisted of isolated broodrearing wetlands in a 17,800-km2 area (McAuley 1986) that extended from eastern Waldo County through Hancock and Washington counties and into northern Penobscot and southwestern Aroostook counties in Maine. This area included most of the wetlands that were studied by Mendall (1958). Bedrock types (i.e., sensitivity class 1 and 2 [no-low and low-medium acid neutralizing capacity]) (Norton et al. 1982a,b) indicated wetlands were vulnerable to acidification (alkalinity 5200 geq/L [Hendrey et al. 1980]). Ducklings were collected from 16 wetlands. Most water samples were collected in July 1983-84. Measurements of water chemistry followed Haines and Akielaszek (1983), except alkalinity was determined by the Gran plot method (Stumm and Morgan 1970) only. During 1983-85, we attempted to collect Class I (?16 days old), II (17-38 days old), and III (39-49 days old) ducklings (Gollop and Marshall 1954) from as many wetlands as possible. We tried to observe ducklings feeding before collecting (Swanson and Bartonek 1970), but because broods were sparsely distributed and often

EFFECTS OF HUNTING ON SURVIVAL OF AMERICAN WOODCOCK IN THE NORTHEAST

Abstract Numbers of American woodcock (Scolopax minor) males counted on the annual singing ground survey (SGS) have declined over the last 35 years at an average rate of 2.3% per year in the Eastern Region and 1.8% per year in the Central Region. Although hunting was not thought to be a cause of these declines, mortality caused by hunters can be controlled. Furthermore, there has been no research on effects of hunting mortality on woodcock populations at local and regional levels on the breeding grounds. We used radiotelemetry to determine survival rates and causes of mortality for 913 woodcock captured during fall 1997–2000 on 7 areas in Maine, New Hampshire, Pennsylvania, and Vermont, USA. Three of 7 sites were closed to hunting. For all sites and all years combined, 176 woodcock died, and 130 were censored, of which 39 were censored mortalities. Predation was the major (n = 134, 76%) cause of mortality. Mammals accounted for 56% of the predation, raptors accounted for 25%, and 19% was attributed to unknown predators. On hunted sites, 36% of the total mortality (n = 102) was caused by hunting, 63% by predation, and 1 bird starved. Kaplan-Meier survival curves did not differ between hunted and non-hunted sites among years (P = 0.46). Overall, point estimates of survival did not differ (P = 0.217) between hunted (SR = 0.636, SE = 0.04) and nonhunted sites (SR = 0.661, SE = 0.08). We modeled hazard rates from hunting and natural mortality events using program MARK. Akaikes Information Criterion supported using a model with common constant hazards from both hunting and natural causes for groups of sites. Groupings of sites for hazard rates from natural causes were not influenced by whether a site was hunted or not. Models detected no effects of woodcock age and sex (P = 0.52) on survival. Proportional hazards models comparing hunted and nonhunted sites found no effects of age and sex (P = 0.45), interactions of age, sex, capture weight, and bill length (P ≥ 0.269). Our data suggest that current hunting regulations are not causing lower survival of woodcock.

Outcome of aggressive interactions between American black ducks and mallards during the breeding season

American black duck (Anas rubripes) numbers have declined during the past several decades, while mallards (A. platyrhynchos) have expanded their range eastward. Competitive exclusion of black ducks from wetlands by mallards has been proposed as a principal cause of the decline. We studied a sympatric population of black ducks and mallards in Maine during the early breeding season to document behavior and interactions. We observed 832 aggressive interactions; most (72%) were interspecific. When a choice was available, both species interacted more often with conspecifics than with the other species (P < 0.028). On wetlands occupied simultaneously by both species, numbers of intraspecific interactions initiated by each species were similar (P = 0.470). The proportions of won (initiator displaces recipient of attack), lost (initiator displaced), and no change outcomes of these interactions were different (P < 0.001). When black ducks initiated interactions with mallards, black ducks did not lose any interactions and displaced mallards 87.2% of the time; no change occurred during 12.8% of the interactions. When mallards initiated interactions with black ducks, mallards displaced black ducks 63.3% of the time but were displaced by black ducks 15.0% of the time; no change occurred during 21.7% of the interactions. Displacement from wetlands was rare (38 of 229 interspecific interactions) and was equal between species.

Habitat Characteristics of American Woodcock Nest Sites on a Managed Area in Maine

We measured characteristics of habitat near 89 nests of American woodcock (Scolopax minor) and 100 randomly selected points on Moosehorn National Wildlife Refuge, Calais, Maine, an area managed for woodcock. At nest sites, basal area was lower (P 0.05) or between sites of successful nests and nests destroyed by predators, although the large variances of the variables reduced our power to detect differences. Habitat around sites of renests differed from sites of first nests. Sites around first nests had lower basal area of dead trees (P = 0.05) and higher stem densities of aspen (P = 0.03) and cherry saplings (Prunus spp.) (P = 0.001), and viburnum (Viburnum spp.) (P = 0.05), while renest sites had taller trees (P = 0.02). The change from nest sites in areas dominated by alders and tree-size gray birch used in 1977-80 to sites dominated by sapling trees, especially aspen, used during 1987-90 suggests that woodcock in the expanding population at the refuge are selecting nest sites created by habitat management since 1979.

Dynamic use of wetlands by black ducks and mallards: evidence against competitive exclusion

Abstract The decline of the American black duck (Anas rubripes) has been attributed to competition from mallards (A. platyrhynchos) that led to exclusive use of fertile wetlands by mallards. Data from annual breeding waterfowl surveys provide instantaneous, single observations of breeding pairs, which are used to estimate breeding population size and evaluate the condition of habitat. Data from these surveys have been used to document habitat use by black ducks and mallards. We used quiet-observation surveys from elevated platforms to study sympatric black ducks and mallards in northern Maine during the breeding season. Our objectives were to document occupancy of wetlands by breeding black ducks and mallards throughout the day during prenesting and early nesting periods to determine whether 1) wetlands were occupied by only a single species, 2) pairs of the same species occupied wetlands throughout the period, and 3) single observations of short duration adequately determine numbers and species using a wetland. We observed ducks at 5-minute intervals from elevated platforms on wetland margins to determine numbers and species of indicated pairs using each wetland over time. We visited 80% of the wetlands ≥2 times, with mean total time per wetland averaging 267 minutes. For each wetland we determined the most frequently observed grouping of black ducks and mallards from all combinations recorded during all intervals (e.g., 1 black duck [BD] pair during 9 intervals; 2 mallard [MA] pairs and 1 BD pair during 22 intervals; 0 pairs during 3 intervals). A single pair, a lone male, or no ducks were recorded during 34% of the 5-minute intervals. For wetlands with ≥2 hours of observations (n=65), all but 2 were used by ≥2 different combinations of ducks. On most wetlands, the most frequent grouping was observed during <40% of the intervals. To simulate aerial surveys, we randomly selected 1 5-minute interval for each wetland. On average, the number of indicated pairs recorded during random 5-minute intervals was less than half of the total black duck pairs (2.0 vs. 4.4, P= 0.009), total mallard pairs (1.1 vs. 2.6, P=0.0001), and pairs of both species combined (3.2 vs. 7.0, P=0.0001) determined for each wetland based on total observations. On wetlands used by both species, random counts detected one or both species 49% of the time. Although 53 of the 65 wetlands observed ≥2 hours were used by both species, random visits detected both species on only 27 wetlands. Our data do not support assertions that the mallard has caused the decline of black ducks through interspecific competition for habitat, or that wetlands are occupied continuously by single pairs that aggressively exclude conspecifics. Our data indicated that single, short-duration visits with disturbance to wetlands are unreliable and inappropriate to document seasonal use of wetlands by breeding black ducks and mallards.

Brood sizes of sympatric American black ducks and mallards in Maine

The long-term decline of the American black duck (Anas rubripes) population has been attributed to lower productivity of black ducks that might have been excluded from fertile agricultural wetlands by mallards (Anas platyrhynchos). We monitored broods on 53 wetlands in 1993 and on 58 wetlands in 1994 to determine mean brood sizes of black ducks and mallards in forested and agricultural landscapes. Study wetlands were moderately to highly fertile. We monitored 94 black duck broods each year and 46 (1993) and 52 (1994) mallard broods until they reached Class IIC-III (near fledging). No differences existed (P = 0.71) in mean brood size between black ducks (1993: 3.95 ± 0.23; 1994: 4.59 ± 0.24) and mallards (1993: 3.96 ± 0.35; 1994: 5.00 ± 0.43) either year. Brood size for species, however, was different between years (P = 0.014) and among wetland sites (P = 0.001). Mean sizes of broods were larger (P < 0.05) on 2 large impoundment complexes (Lake Josephine and Lake Christina) compared with brood sizes on other wetlands in forested or agricultural landscapes. No differences (P ≥ 0.41) existed between mean Class IIc-III brood sizes of black ducks and mallards, whether species were alone or together on wetlands. Our data document that mallard productivity is similar to that of black ducks where they breed sympatrically in Maine.

Habitat use by postfledging american black ducks in Maine and New Brunswick

We examined habitat use by 112 postfledging American black ducks (Anas rubripes) in eastern Maine and southwestern New Brunswick from September through early December of 1985, 1986, and 1987. Ducks were captured on Moosehorn National Wildlife Refuge (NWR), Maine. Palustrine Emergent Wetland was the most preferred habitat type. Riverine habitats were avoided in September, but were used more than, or in proportion to, their availability in November as ice formed on lentic habitats. Black ducks used a greater variety of habitat types during the day than at night, when ducks used mostly large (>30 ha) Emergent Wetland marshes. Managed impoundments of Moosehorn NWR were the most used wetlands (66% of all diurnal, 90% of all nocturnal locations). For black duck management, we propose maintaining large (30-50 ha) marshes containing dense emergent vegetation that are located near a complex of diverse wetland types. J. WILDL. MANAGE. 54(3):451-459 Habitat use by breeding American black ducks has been documented for northeastern North America (Coulter and Mendall 1968, Coulter and Miller 1968, Reed 1975, Ringelman 1980, Diefenbach 1988) and for mid-Atlantic saltmarshes (Stotts and Davis 1960). Most research on postbreeding ducks has involved adult birds during wing molt (Gilmer et al. 1977, Bowman 1987), whereas little is known of habitat use by young waterfowl after fledging. Data on habitat use by postfledging black ducks are lacking, and this period of the annual cycle might be critical to survival (Ringelman and Longcore 1980). Our objective was to describe daily and seasonal habitat use by postfledging black ducks. We thank field assistants B. E. Benedict, J. S. Henderson, R. A. Houston, J. D. Sayre, R. T. Speer, and D. B. Stotts. G. E. Horton, M. K. Meiman, and E. P. Schrading assisted with data entry. W. A. Halteman and S. M. Arthur provided statistical advice. D. G. Jorde and J. A. Spendelow reviewed the manuscript. Financial support was provided by the U.S. Fish and Wildlife Service through Cooperative Agreement No. 14-16-0009-1557, Research Work Order No. 2 with the University of Maine.