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Rolf R. Koford

Publications and source records attributed to Rolf R. Koford.

16 recordsLinked to original sources
USGS2011

Habitat and landscape effects on abundance of Missouri's grassland birds

Of 6 million ha of prairie that once covered northern and western Missouri, <36,500&thinsp;ha remain, with planted, managed, and restored grasslands comprising most contemporary grasslands. Most grasslands are used as pasture or hayfields. Native grasses largely have been replaced by fescue ( Festuca spp.) on most private lands (almost 7 million ha). Previously cropped fields set aside under the Conservation Reserve Program (CRP) varied from a mix of cool-season grasses and forbs, or mix of native warm-season grasses and forbs, to simple tall-grass monocultures. We used generalized linear mixed models and distance sampling to assess abundance of 8 species of breeding grassland birds on 6 grassland types commonly associated with farm practices in Missouri and located in landscapes managed for grassland-bird conservation. We selected Bird Conservation Areas (BCAs) for their high percentage of grasslands and grassland-bird species, and for <5% forest cover. We used an information-theoretic approach to assess the relationship between bird abundance and 6 grassland types, 3 measures of vegetative structure, and 2 landscape variables (% grassland and edge density within a 1-km radius). We found support for all 3 levels of model parameters, although there was less support for landscape than vegetation structure effects likely because we studied high-percentage-grassland landscapes (BCAs). Henslow's sparrow ( Ammodramus henslowii ) counts increased with greater percentage of grassland, vegetation height-density, litter depth, and shrub cover and lower edge density. Henslow's sparrow counts were greatest in hayed native prairie. Dickcissel ( Spiza americana ) counts increased with greater vegetation height-density and were greatest in planted CRP grasslands. Grasshopper sparrow ( A. savannarum ) counts increased with lower vegetation height, litter depth, and shrub cover. Based on distance modeling, breeding densities of Henslow's sparrow, dickcissel, and grasshopper sparrow in the 6 grassland types ranged 0.9&ndash;2.6, 1.4&ndash;3.2, and 0.1&ndash;1.5&thinsp;birds/ha, respectively. We suggest different grassland types and structures (vegetation height, litter depth, shrub cover) are needed to support priority grassland-bird species in Missouri.

Journal of Wildlife Management↗
USGS2011

Postfledging survival of Grasshopper Sparrows in grasslands managed with fire and grazing

More accurate estimates of survival after nestlings fledge are needed for population models to be parameterized and population dynamics to be understood during this vulnerable life stage. The period after fledging is the time when chicks learn to fly, forage, and hide from predators. We monitored postfledging survival, causespecific mortality, and movements of Grasshopper Sparrows ( Ammodramus savannarum ) in grassland managed with fire and grazing. In 2009, we attached radio transmitters to 50 nestlings from 50 different broods and modeled their survival in response to climatic, biological, and ecological variables. There was no effect of treatment on survival. The factor most influencing postfledging survival was age; no other variable was significant. The majority of chicks (74%) died within 3 days of radio-transmitter attachment. We attributed most mortality to mesopredators (48%) and exposure (28%). Fledglings' movements increased rapidly for the first 4 days after they left the nest and were relatively stable for the remaining 10 days we tracked them. On average, fledglings took flight for the first time 4 days after fledging and flew &ge;10 m 9 days after fledging. Our data show that the Grasshopper Sparrow's survival rates may be less than most models relying on nest-success estimates predict, and we emphasize the importance of incorporating estimates of survival during the postfledging period in demographic models.

Iowa↗
USGS2011

Bat mortality and activity at a Northern Iowa wind resource area

We examined bat collision mortality, activity and species composition at an 89-turbine wind resource area in farmland of north-central Iowa from mid-Apr. to mid-Dec., 2003 and mid-Mar. to mid-Dec., 2004. We found 30 bats beneath turbines on cleared ground and gravel access areas in 2003 and 45 bats in 2004. After adjusting for search probability, search efficiency and scavenging rate, we estimated total bat mortality at 396 ?? 72 (95 ci) in 2003 and 636 ?? 112 (95 ci) in 2004. Although carcasses were mostly migratory tree bats, we found a considerable proportion of little brown bats (Myotis lucifugus). We recorded 1465 bat echolocation call files at turbine sites ( 34.88 call files/detector-night) and 1536 bat call files at adjacent non-turbine sites ( 36.57 call files/detector-night). Bat activity did not differ significantly between turbine and non-turbine sites. A large proportion of recorded call files were made by Myotis sp. but this may be because we detected activity at ground level only. There was no relationship between types of turbine lights and either collision mortality or echolocation activity. The highest levels of bat echolocation activity and collision mortality were recorded during Jul. and Aug. during the autumn dispersal and migration period. The fatality rates for bats in general and little brown bats in particular were higher at the Top of Iowa Wind Resource Area than at other, comparable studies in the region. Future efforts to study behavior of bats in flight around turbines as well as cumulative impact studies should not ignore non-tree dwelling bats, generally regarded as minimally affected. ?? 2011, American Midland Naturalist.

American Midland Naturalist↗
USGS2011

Assessing the role of conspecific attraction in habitat restoration for Henslow's sparrows in Iowa

The presence of conspecific individuals may provide important cues about habitat quality for territorial songbirds. We tested the ability of a conspecific song playback system to attract Henslow&rsquo;s sparrows to previously unoccupied restored habitat. We successfully attracted Heslow&rsquo;s sparrows to 3 of 7 treatment plots using conspecific song playbacks and we found no Henslow&rsquo;s sparrows in control plots. The addition of social cues using playback systems in restored grassland habitats may aid conservation efforts of Henslow&rsquo;s sparrows to available habitat.

Iowa↗
USGS2010

Direct and indirect responses of tallgrass prairie butterflies to prescribed burning

Fire is an important tool in the conservation and restoration of tallgrass prairie ecosystems. We investigated how both the vegetation composition and butterfly community of tallgrass prairie remnants changed in relation to the elapsed time (in months) since prescribed fire. Butterfly richness and butterfly abundance were positively correlated with the time since burn. Habitat-specialist butterfly richness recovery time was greater than 70 months post-fire and habitat-specialist butterfly abundance recovery time was approximately 50 months post-fire. Thus, recovery times for butterfly populations after prescribed fires in our study were potentially longer than those previously reported. We used Path Analysis to evaluate the relative contributions of the direct effect of time since fire and the indirect effects of time since fire through changes in vegetation composition on butterfly abundance. Path models highlighted the importance of the indirect effects of fire on habitat features, such as increases in the cover of bare ground. Because fire return intervals on managed prairie remnants are often less than 5 years, information on recovery times for habitat-specialist insect species are of great importance. ?? 2010 Springer Science+Business Media B.V.

Journal of Insect Conservation↗
USGS2003

Spatial responses of bobolinks ( Dolichonyx oryzivorus ) near different types of edges in Northern Iowa

Habitat edges are well-studied components of fragmented landscapes, yet factors mediating edge effects remain unclear. We report how different types of edges surrounding patches may affect spatial distributions of Bobolink ( Dolichonyx oryzivorus ), a declining, area-sensitive songbird that breeds in grasslands. We expected Bobolinks to be less abundant near edges, and we investigated a set of alternative hypotheses for explaining that spatial pattern: (1) passive displacement, in which individuals do not avoid edges but use edges as boundaries for territories; (2) habitat gradients, in which individuals respond to habitat structure gradients near edges; (3) territory size, in which size of territories increases near edges; and (4) active avoidance, in which individuals actively avoid edges by positioning territory boundaries away from edges. To examine those hypotheses, we surveyed Bobolinks in grassland habitats near 34 edges of three different edge types (agriculture, road, and woodland) in northern Iowa, 1999–2000. Bobolink density was lower near woodland edges than near other edge types, and density increased as a function of distance from edge for all edge types. There was no evidence for a habitat gradient close to edges, but there was some evidence for habitat structure differing among edge types. Territory size increased near roads, decreased near woodlands, but did not change near agricultural edges. Territory positioning was consistent with active avoidance near woodland edges, and to a lesser extent road edges, but positioning was only consistent with passive displacement near agriculture edges. We conclude that land use surrounding patches can have variable effects on territorial dynamics and habitat use of this area-sensitive species. Linking edge avoidance with fitness is needed to understand the demographic consequences of those responses for species in fragmented landscapes.

The Auk↗
USGS2002

Habitat and landscape associations of breeding birds in native and restored grasslands

In the midwestern United States, less than 1% of the original tallgrass prairie ecosystem remains. State and federal agencies have responded to this habitat loss with programs and land acquisition that have increased the amount of grassland on the landscape by restoring grassland from other land-use practices. We assessed the effects of habitat restoration and the relative contribution of local habitat and landscape factors on breeding grassland birds in northern Iowa. During the 1999 and 2000 breeding seasons, we surveyed grassland birds in 10 tallgrass prairies and 10 restored grasslands that contained a wide diversity of habitat and landscape conditions. Densities of common bird species were similar between habitat types, except for grasshopper sparrows (Ammodramus savannarum) and savannah sparrows (Passerculus sandwichensis), which were 4 and 9 times more dense in restored grasslands, respectively. Species richness of breeding birds was similar between habitat types. Habitat structure was different in prairies and restored grasslands; restored grasslands had 7% less total vegetation cover and 3% more bare ground. A nested, multiscale analysis indicated that habitat structure explained some variation in species richness and bird density of all common species, yet addition of landscape structure improved models for species richness and for density of 4 of 8 species considered, explaining an additional 10-29% of the variation. Edge-density metrics were the most common variables entering into landscape models; most species had lower densities in landscapes with high edge density. Our results indicate that restored grassland habitats contain bird communities generally similar to those in native prairie habitats in northern Iowa, suggesting that restored grasslands may provide similar habitat suitability for most grassland birds. In addition, both local habitat and landscape factors can be important for managing breeding grassland birds.

Journal of Wildlife Management↗
USGS2000

Cowbird parasitism in grassland and cropland in the northern Great Plains

The landscape of the Great Plains has been greatly altered by human activities in the past century, and several grassland passerines have experienced significant population declines in recent decades. We explore here whether brood parasitism by Brown-headed Cowbirds, which are abundant in the Great Plains, has contributed to these declines. We measured the frequency of cowbird parasitism of passerine species in seeded grassland, natural grassland, and cropland in studies conducted in North Dakota during 1981-1993. The proportions of parasitized nests were 25%, 34%, and 39% in seeded grassland, natural grassland, and cropland, respectively. We speculate that much of the variation in parasitism rate among these habitats is related to the local abundance of cowbirds, to nest visibility, and to the presence of suitable perches for female cowbirds. Local abundance of cowbirds may be high in areas with cattle pastures. Nests and nesting behavior are probably more visible to female cowbirds in cropland than in grassland. Female cowbirds may use shrubs as perches while searching for host nests, and shrubs are more common in natural grasslands than in the other habitats we examined. Experimental work on the determinants of cowbird abundance in grasslands is needed.

Book chapter↗
USGS1996

Long-term declines in nest success of prairie ducks

Increased predation on nests of ducks in prairie uplands, as a result of habitat alteration, has been hypothesized to cause decreased nest success and population sizes. We tested whether, and by how much, nest success declined using data compiled from 37 studies conducted between 1935 and 1992 at 67 sites in the Prairie Pothole Region of Canada and the United States. Nest success declined (P = 0.0002) over time, but time explained only 10% of the variation; precipitation ( P = 0.79) did not account for additional variation in nest success. Nest success declined at similar ( P = 0.13) rates among 5 species, but late nesters (gadwall [Anas strepera], blue-winged teal [ A. discors ] and northern shoveler [ A. clypeata ]) had higher success ( P = 0.004) than early nesters (mallard [ A. platyrhynchos ] and northern pintail [ A. acuta ]). Populations of gadwalls and northern shovelers, however, have not declined, indicating that declines in nest success may not be related causally to population change. Long-term population declines in blue-winged teal, northern pintails, and mallards coincide with large-scale temporal declines in nest success. Declines in nest success were parallel in parkland and grassland regions, suggesting a causal agent (or agents) that act(s) at a broad scale, despite inherent differences in the composition of the predator communities and habitats between regions.

Prairie Pothole Region↗
USGS1995

Conservation Reserve Program and migratory birds in the northern Great Plains

U.S. Department of Agriculture programs have mediated supply and demand of commodities and maintained the agricultural industry, but several programs have also offered various kinds of conservation benefits. The 1985 Food Security Act (Farm Bill) featured the Conservation Reserve Program (CRP), which paid farmers to plant perennial cover on highly erodible lands and to leave this land intact for a 10-year contract period. During that period we conducted two studies to determine the value of CRP fields to breeding birds in the northern Great Plains.

Great Plains↗
USGS1992

A stochastic population model of mid-continental mallards

We developed a simulation model that integrates infonnation on factors affecting the population dynamics of mallards in the mid-continental region of the United States. In the model we vary age, body mass, and reproductive and molt status of simulated females. Females use several types of nesting and foraging habitat in 15 geographic areas. Deterministic and stochastic events cause mortality or attribute changes on a daily basis, depending on current attributes, habitat, area, calendar date, wetland conditions, temperature, and various mortality agents. Because the model encompasses the entire year, it can be used to examine cross-seasonal effects. A simulated increase in nest success from 0.14 to 0.17 changed the annual rate of population growth from -6% to -1 %. A simulated 75% reduction in lead poisoning changed the rate from -6% to -3%.

Book chapter↗
USGS1989

Dispersal in the communally breeding groove-billed ani (Crotophaga sulcirostris)

We studied dispersal in a color-banded population of the Groove-billed Ani (Crotophaga sulcirostris) in Costa Rica. Eight percent of the young alive at the end of the breeding season bred on their natal territories the next year and 4% remained but did not breed. Thirteen percent dispersed successfully within the study area and bred in communal groups or simple pairs. The remaining 75% of the young birds disappeared from the study area. Young males remained in the study area as breeders more frequently than did young females. Breeding dispersal occurred, with at least 9% of the adult population moving to a new territory each year.We used a demographic model to estimate the following dispersal fates for young birds. For both males and females, 62% of the young alive at the end of the breeding season in which they hatched obtained a breeding position the next year. Of those that dispersed from their natal territories, 59 to 70% of the males and 64 to 74% of the females obtained breeding positions. Of those that bred the year after they hatched, 22% of the males and 2% of the females bred in their natal units, 34% of the males and 6% of the females bred within the study area but outside their natal units, and 44% of the males and 92% of the females bred outside the study area. We estimated that all of the males and 28% of the females that bred the year after they hatched were within three territories of their natal sites.

Condor↗