Temporal Flexibility of Reproduction in Temperate-Breeding Dabbling Ducks

I compared nesting intervals during three consecutive years in five species of temperate-nesting dabbling ducks (Mallard [Anas platyrhynchos], Northern Pintail [Anas acuta], Northern Shoveler [Anas clypeata], Blue-winged Teal [Anas discors], Gadwall [Anas strepera]) and assessed whether differences existed in timing of refractoriness. Most nesting by females of all five species ended by the summer solstice. Nesting ended earliest for Northern Shovelers and Northern Pintails and latest for Gadwalls. Some Mallards, Blue-winged Teal, and Gadwalls continued to nest into mid- and late summer, whereas Northern Shovelers and Northern Pintails did not. Mallards, Blue-winged Teal, and Gadwalls accounted for 99% (81 of 82) of flightless broods resulting from nests initiated during mid- or late summer in North Dakota and 98% (58 of 59) of flightless juveniles shot on or after 1 October by a random sample of duck hunters from across the United States. Early cessation of breeding by Northern Shovelers may have evolved in response to the species’ limited flexibility in diet. Photo-refractory mechanisms that limit most breeding to spring presumably evolved in response to severe constraints on reproductive success when nesting continued through summer (e.g. mortality of late-hatched young and molting females due to low temperatures). Interspecific differences in photosensitivity may account for variation in timing of cessation of nesting in late spring, but controlled experiments are needed to assess the possible role of non-photic influences. My results suggest that the refractory mechanisms controlling length of the breeding season in temperate-nesting dabbling ducks are more varied and complex than previously thought, with non-photic influences (e.g. water conditions, food availability, food quality) having a larger role than indicated by earlier research

Temporal Flexibility of Reproduction in Temperate-Breeding Dabbling Ducks

I compared nesting intervals during three consecutive years in five species of temperate-nesting dabbling ducks (Mallard [Anas platyrhynchos], Northern Pintail [Anas acuta], Northern Shoveler [Anas clypeata], Blue-winged Teal [Anas discors], Gadwall [Anas strepera]) and assessed whether differences existed in timing of refractoriness. Most nesting by females of all five species ended by the summer solstice. Nesting ended earliest for Northern Shovelers and Northern Pintails and latest for Gadwalls. Some Mallards, Blue-winged Teal, and Gadwalls continued to nest into mid- and late summer, whereas Northern Shovelers and Northern Pintails did not. Mallards, Blue-winged Teal, and Gadwalls accounted for 99% (81 of 82) of flightless broods resulting from nests initiated during mid- or late summer in North Dakota and 98% (58 of 59) of flightless juveniles shot on or after 1 October by a random sample of duck hunters from across the United States. Early cessation of breeding by Northern Shovelers may have evolved in response to the species’ limited flexibility in diet. Photo-refractory mechanisms that limit most breeding to spring presumably evolved in response to severe constraints on reproductive success when nesting continued through summer (e.g. mortality of late-hatched young and molting females due to low temperatures). Interspecific differences in photosensitivity may account for variation in timing of cessation of nesting in late spring, but controlled experiments are needed to assess the possible role of non-photic influences. My results suggest that the refractory mechanisms controlling length of the breeding season in temperate-nesting dabbling ducks are more varied and complex than previously thought, with non-photic influences (e.g. water conditions, food availability, food quality) having a larger role than indicated by earlier research

Sandhill Crane Roost Selection, Human Disturbance, and Forage Resources

Sites used for roosting represent a key habitat requirement for many species of birds because availability and quality of roost sites can influence individual fitness. Birds select roost sites based on numerous factors, requirements, and motivations, and selection of roosts can be dynamic in time and space because of various ecological and environmental influences. For sandhill cranes (Antigone canadensis) at their main spring staging area along the Platte River in south-central Nebraska, USA, past investigations of roosting cranes focuse donphysical channel characteristics related to perceived security as motivating roost distribution.We used 6,310 roost sites selected by 313 sandhill cranes over 5 spring migration seasons (2003–2007) to quantify resource selection functions of roost sites on the central Platte River using a discrete choice analysis. Sandhill cranes generally showed stronger selection for wider channels with shorter bank vegetation situated farther from potential human disturbance features such as roads, bridges, and dwellings.Furthermore, selection for roost sites with preferable physical characteristics (wide channels with short bank vegetation) was more resilient to nearby disturbance features than more narrow channels with taller bank vegetation. The amount of cornfields surrounding sandhill crane roost sites positively influenced relative probability of use but only for more narrow channels \u3c100m and those with shorter bank vegetation. We confirmed key resource features that sandhill cranes selected at river channels along the Platte River, and after incorporating spatial variation due to human disturbance, our understanding of roost site selection was more robust, providing insights on how disturbance may interact with physical habitat features. Managers can use information on roost-site selection when developing plans to increase probability of crane use at existing roost sites and to identify new areas for potential use if existing sites become limited

Conditioning of Sandhill Cranes During Fall Migration

Body mass of adult female and male sandhill cranes (Grus canadensis) increased an average of 17 and 20%, respectively, from early September to late October on staging areas in central North Dakota and varied by year. Increases in body mass averaged 550 and 681 g among female and male G. c. canadensis, respectively, and 616 and 836 g among female and male G. c. rowani. Adult and juvenile G. c. rowani were lean at arrival, averaging 177 and 83 g of fat, respectively, and fat reserves increased to 677 and 482 g by mid-October. Fat-free dry mass increased by 12% among juveniles, reflecting substantial growth, but remained constant among adults. The importance of fall staging areas as conditioning sites for sandhill cranes, annual variation in body mass, and vulnerability of cranes to habitat loss underscore the need to monitor status of fall staging habitat in the northern plains region and to take steps to maintain suitable habitat where necessary

Feeding Ecology of Arctic-Nesting Sandpipers During Spring Migration Through the Prairie Pothole Region

We evaluated food habits of 4 species of spring-migrant calidrid sandpipers in the Prairie Pothole Region (PPR) of North Dakota. Sandpipers foraged in several wetland classes and fed primarily on aquatic dipterans, mostly larvae, and the midge family Chironomidae was the primary food eaten. Larger sandpiper species foraged in deeper water and took larger larvae than did smaller sandpipers. The diverse wetland habitats that migrant shorebirds use in the PPR suggest a landscape-level approach be applied to wetland conservation efforts. We recommend that managers use livestock grazing and other tools, where applicable, to keep shallow, freshwater wetlands from becoming choked with emergent vegetation limiting chironomid production and preventing shorebird use

USE OF SATELLITE TELEMETRY TO IDENTIFY TEMPORAL AND SPATIAL DISTRIBUTION OF THE MIDCONTINENT SANDHILL CRANE POPULATION THROUGHOUT THE ANNUAL CYCLE

Effective management of the midcontinent sandhill crane (Grus canadensis) population requires having detailed information available on the distribution of subspecies and subpopulations throughout the annual cycle. The current study is being undertaken in partnership with several federal and state agencies and private organizations to obtain key information not currently available. We are monitoring crane movements throughout the year by attaching Platform Transmitting Terminals (PTTs) to plastic leg bands and with the aid of equipment on board orbiting NOAA weather satellites relocating the radiomarked individuals at 4-10 day intervals throughout the year. Twenty-one cranes were captured and radio-marked in the Central Platte River Valley in early spring 1998 and 1999. Results to date indicate the technique is well suited for obtaining the types of information being sought. Most of the radio-marked cranes after departing from the Platte River in spring staged again at sites in southern Saskatchewan but those of the Canadian subspecies (G. c. rowan i) breeding in Manitoba and Ontario staged in northwestern Minnesota. Distnbution of radio-marked individuals on the breeding grounds suggests that northeastern Russia may be a more important breeding area for lesser sandhill cranes (G. c. canadensis) than previously thought; 50% of lesser sandhill cranes tagged to date (6 of 12) migrated to locations in northeastern Siberia. Onset offall migration occurred from mid-August to mid-September depending on latitude; fall staging was centered primarily in 3 areas of southern Saskatchewan with fewer radio-marked cranes staging in southwestern Manitoba and central North Dakota. Most radio-marked cranes have spent winter in west Texas, 2 (both G. c. rowani) have occupied sites near the Texas Gulf Coast, and 1 each spent winter at sites in Arizona and New Mexico (both G. c. canadensis breeding in northeastern Siberia). Habitats occupied by cranes are being identified throughout the annual cycle with the aid of GIS methodology as are temporal and spatial patterns of use of the Central Platte River Valley. Information obtained from the study will be used to delineate breeding ranges, migration corridors, staging areas, and wintering grounds of subspecies and subpopulations to allow crane managers to better meet the needs of the midcontinent population. Current plans are to gather information on a total of 200 sandhill cranes over the study period with 42 cranes to be radio marked in 2000. Those interested in following the radio-marked cranes during their annual cycle or learning more about the crane study can do so by logging on our web site at www.npwrc.usgs.gov/perm/cranemov/cranmov.htm

Fat Deposition and Usage by Arctic-Nesting Sandhill Cranes During Spring

Body weight, fat, and protein levels of arctic-nesting Sandhill Cranes (Grus canadensis) were measured at several locations during spring migration and on the breeding grounds. Body weights of adult males and females increased by about 34%( 1,129 g) and 30% (953 g) from early March at the Platte River to late April at Last Mountain Lake, Saskatchewan; average fat content increased from about 250 to 990 g. Rates of weight gain and fat deposition among males and females averaged 25-18 and 16-13 g/day. Body weights and fat content of cranes staging along the North Platte River followed similar patterns and usually were higher than along the Platte River during comparable periods. Fat reserves of paired cranes collected after their arrival at a major breeding ground on the Yukon-Kuskokwim Delta in western Alaska averaged about 530 g, or about 46% less than peak fat content in Saskatchewan. Patterns of weight increase and fat deposition in cranes during migration were similar to those previously described for northern-nesting geese, except that nutrient storage is not sex specific in cranes. Body protein of adult female cranes did not change significantly during spring migration (P = 0.28). Female cranes allocate less nutrients to clutch formation in proportion to body size than do northern-nesting geese

Yellow-crowned Night Herons Sighted in North Dakota

Yellow-crowned night herons (Nyctanassa violacea) sighted at four locations in North Dakota during 1976 appear to be the first observations of this species for the State. We sighted a single individual about 8 km south of Medina, North Dakota in western Stutsman County during several visits in June and July 1976. The bird was first seen on 23 June standing in a pasture adjoining an 8.5 ha semi-permanent marsh. On following visits, the heron usually was seen perched in trees at the edge of the wetland. A single yellow-crowned night heron was sighted on the same wetland on three separate occasions in June 1977. It is not known whether this was the same individual that was seen in 1976. The wetland contains dense stands of cattail (Typha spp.), hardstem bulrush (Scirpus acutus), and reed (Phragmites communis), and is bordered by open stands of cottonwood (Populus deltoides) and peach-leaved willow (Salix amygdaloides). Several black-crowned night herons (Nycticorax nycticorax) also were observed at the marsh during 1976 and 1977. Herons may have been attracted to the wetland by the presence of large numbers of leopard frogs (Rana pipiens). No yellow-crowned night heron nests were found during nest searches of the wetland in 1976 and 1977