Birds In Agricultural Landscapes Research Articles

Grassland Bird Responses to Land Management in the Largest Remaining Tallgrass Prairie

Extensive habitat loss and changing agricultural practices have caused widespread declines in grassland birds throughout North America. The Flint Hills of Kansas and Oklahoma--the largest remaining tallgrass prairie--is important for grassland bird conservation despite supporting a major cattle industry. In 2004 and 2005, we assessed the community, population, and demographic responses of grassland birds to the predominant management practices (grazing, burning, and haying) of the region, including grasslands restored under the Conservation Reserve Program (CRP). We targeted 3 species at the core of this avian community: the Dickcissel (Spiza americana), Grasshopper Sparrow (Ammodramus savannarum), and Eastern Meadowlark (Sturnella magna). Bird diversity was higher in native prairie hayfields and grazed pastures than CRP fields, which were dominated by Dickcissels. Although Dickcissel density was highest in CRP, their nest success was highest and nest parasitism by Brown-headed Cowbirds (Moluthrus ater) lowest in unburned hayfields (in 2004). Conversely, Grasshopper Sparrow density was highest in grazed pastures, but their nest success was lowest in these pastures and highest in burned hayfields, where cowbird parasitism was also lowest (in 2004). Management did not influence density and nest survival of Eastern Meadowlarks, which were uniformly low across the region. Nest success was extremely low (5-12%) for all 3 species in 2005, perhaps because of a record spring drought. Although the CRP has benefited grassland birds in agricultural landscapes, these areas may have lower habitat value in the context of native prairie. Hayfields may provide beneficial habitat for some grassland birds in the Flint Hills because they are mowed later in the breeding season than elsewhere in the Midwest. Widespread grazing and annual burning have homogenized habitat-and thus grassland-bird responses-across the Flint Hills. Diversification of management practices could increase habitat heterogeneity and enhance the conservation potential of the Flint Hills for grassland birds.

Nest predation of Common Pheasants Phasianus colchicus

The Common Pheasant Phasianus colchicus is currently the most abundant, widespread and economically important gamebird in Europe. The Game and Wildlife Conservation Trust has undertaken several recent studies of Pheasant breeding ecology to improve the management of this species. Although predation is often the most important cause of nest failure in declining ground‐nesting birds in agricultural landscapes, the causes of predation and the identity of predators are often unknown. In this paper, we analyse data from approximately 450 nests of radiotagged hen Pheasants collected from six sites between 1990 and 2003 and present results on the fate and survival rates of Pheasant nests in relation to habitat, predation control and other covariates. Survival rates during the laying stage and incubation stage were 28 and 37%, respectively, and overall nest survival was 10%. Nest predation rates were significantly lower on two sites where intensive predation control was undertaken than on four sites with only low levels of predation control. Red Foxes Vulpes vulpes and corvids were the most important nest predators, accounting for at least half of all predation events. We assess these results in the context of other ground‐nesting farmland birds.

Colonisation of native tree and shrub plantings by woodland birds in an agricultural landscape

Tree planting has become a cornerstone strategy for natural resource management in agricultural landscapes, yet its contribution as habitat for woodland birds has not been fully investigated. A case study from the Holbrook region in southern New South Wales was used to assess woodland birds in young plantings of native trees and shrubs. Ground-foraging insectivorous woodland birds were under-represented in the plantings, partly due to a lack of native forb diversity (wildflowers) and leaf litter. Of 69 woodland bird species recorded over a three-year period, 48 species (70%) occurred in planted sites, 59 species (86%) occurred in remnant woodland, and 34 species (49%) occurred in adjacent paddock sites. The greater diversity of birds in planted sites relative to paddock sites was mostly due to understorey birds. The proportion of mist-netted birds recaptured was similar in both planted (15%) and remnant woodland (16%) sites, suggesting that individual birds were staying in planted sites. The proportion of woodland birds showing breeding activity (as measured by the presence of a brood patch) was slightly lower in planted sites (24% of all woodland species) than in remnant woodland (29%). Birds such as the superb fairy-wren, red-browed finch and southern whiteface were more likely to occur in planted sites, suggesting that plantings provide unique, transitional-stage habitat within agricultural landscapes. Restoring native forbs, as part of a broader strategy of woodland management, will help to reverse the decline of ground-foraging insectivorous woodland birds in agricultural landscapes.

Accuracy assessment of digitized and classified land cover data for wildlife habitat

Increasing availability of land cover data offers new opportunities for landscape-level environmental research. Accuracy reports for these data are frequently high, but for landscape-level studies, accuracy reports can be misleadingly optimistic. Focusing on land cover classes representing wildlife habitat, this paper compares the extent, size, and shape of land cover classes in two classified data sets and in data digitized by hand for the study areas from aerial photographs. Digitized study areas, selected for use in a study of birds in agricultural landscapes, were distributed across nine counties in southern MN, USA. Classified data sets were created, mainly from remotely sensed imagery, by the U.S. Geological Survey (national landcover characterization data) and the state of Minnesota. Agreement between these layers and digitized data was highest for the most abundant land cover class (croplands) and for water. Agreement was lower than reported in data documentation for woodlands, grasslands, and wetlands. Contrary to expectations, small and rare features were not necessarily lost in remotely sensed data, but some ecologically important features, such as streams, were better retained in the digitized data. Digitized data represented habitat classes best in this study. Growing access to data and remote sensing software could make study-specific classified data a better option in the future.

The effects of habitat structure on predation risk of birds in agricultural landscapes

It has been suggested that increased predation rates may rival habitat alteration as a causal agent in farmland bird population declines. Such a view may be over‐simplistic, however, as changes in habitat structure may influence habitat selection and foraging efficiency through their influence on perceived and actual predation risk. We review evidence from the literature on the effects of habitat structure on predation risk of foraging and nesting birds and apply these principles to investigate the likely effects on the 20 species that comprise the UK Government's ‘Farmland Bird Index’. Shorter vegetation is likely to enhance foraging efficiency and reduce predation risk (when ground foraging) for 15 of the 20 species. However, within grassland systems longer vegetation is known to enhance food supplies (e.g. Tipulid larvae and voles) of several farmland bird species and so mosaics of short and long vegetation may provide the optimum conditions for most species (e.g. LapwingVanellus vanellus, StarlingSturnus vulgaris, Barn OwlTyto alba). Agricultural intensification has encouraged uniform dense swards, thus reducing habitat diversity, and agri‐environment schemes that provide heterogeneous sward structure may thus facilitate farmland bird conservation. Intensification has also resulted in less dense hedgerows; although a reversal of this trend may improve foraging efficiency for many species, it may be detrimental to a smaller number of species that prefer shorter, less dense hedges for nesting. Before these tentative conclusions can be confirmed, more research is required that considers how the effects of habitat structure on individuals is likely to translate into population‐level impacts.

A Review and Synthesis of Habitat Use by Breeding Birds in Agricultural Landscapes of Iowa

Existing information on bird species composition, abundance and nesting sta- tus during the breeding season (May through July) was compiled for habitats characteristic of the agricultural landscapes of Iowa. Data were derived from 60 sources for 144 bird species in 20 habitats. Total numbers of breeding bird species were highest in floodplain forest (107 species) and upland forest (85), and lowest in small grains (31) and herbaceous fencerows (27). Species abundances were standardized and categorized on a scale from 0 (absent) through 5 (very abundant with >250 individual birds/census count/100 ha). Bird species abundances are lowest in some agricultural habitats (e.g., tilled row crops and small grains) and highest in narrow, strip-cover habitats (e.g., railroad rights-of-way, wooded fencerows and farmstead shelterbelts). Species abundance patterns in natural habitats (forest, marsh and prairie) are intermediate between those in agricultural and strip-cover habitats. Twenty-five species occurred only in forest habitats and 14 only in marshes. Other species selectively (through not exclusively) use tilled row crop, grassland or wooded habitats. Principal com- ponents analysis was used to assess the relative similarities in use of the 20 habitats by the assemblage of breeding birds in Iowa. Predicted numbers of nesting species increased from 18 to 93 over four landscape scenarios representing a progression from an intensively farmed row-crop monoculture to a diverse mosaic of crop and noncrop habitats. Although laborious, the approach developed in our study has been useful for standardizing and synthesizing a diverse literature in efforts to conduct ecological risk assessments for farmland birds. It can also provide valuable baseline data for landscape-level research.