Eric M. Wood

Image texture predicts avian density and species richness.

For decades, ecologists have measured habitat attributes in the field to understand and predict patterns of animal distribution and abundance. However, the scale of inference possible from field measured data is typically limited because large-scale data collection is rarely feasible. This is problematic given that conservation and management typical require data that are fine grained yet broad in extent. Recent advances in remote sensing methodology offer alternative tools for efficiently characterizing wildlife habitat across broad areas. We explored the use of remotely sensed image texture, which is a surrogate for vegetation structure, calculated from both an air photo and from a Landsat TM satellite image, compared with field-measured vegetation structure, characterized by foliage-height diversity and horizontal vegetation structure, to predict avian density and species richness within grassland, savanna, and woodland habitats at Fort McCoy Military Installation, Wisconsin, USA. Image texture calculated from the air photo best predicted density of a grassland associated species, grasshopper sparrow (Ammodramus savannarum), within grassland habitat (R2 = 0.52, p-value <0.001), and avian species richness among habitats (R2 = 0.54, p-value <0.001). Density of field sparrow (Spizella pusilla), a savanna associated species, was not particularly well captured by either field-measured or remotely sensed vegetation structure variables, but was best predicted by air photo image texture (R2 = 0.13, p-value = 0.002). Density of ovenbird (Seiurus aurocapillus), a woodland associated species, was best predicted by pixel-level satellite data (mean NDVI, R2 = 0.54, p-value <0.001). Surprisingly and interestingly, remotely sensed vegetation structure measures (i.e., image texture) were often better predictors of avian density and species richness than field-measured vegetation structure, and thus show promise as a valuable tool for mapping habitat quality and characterizing biodiversity across broad areas.

Housing development erodes avian community structure in U.S. protected areas

Protected areas are a cornerstone for biodiversity conservation, but they also provide amenities that attract housing development on inholdings and adjacent private lands. We explored how this development affects biodiversity within and near protected areas among six ecological regions throughout the United States. We quantified the effect of housing density within, at the boundary, and outside protected areas, and natural land cover within protected areas, on the proportional abundance and proportional richness of three avian guilds within protected areas. We developed three guilds from the North American Breeding Bird Survey, which included Species of Greatest Conservation Need, land cover affiliates (e.g., forest breeders), and synanthropic species associated with urban environments. We gathered housing density data for the year 2000 from the U.S. Census Bureau, and centered the bird data on this year. We obtained land cover data from the 2001 National Land Cover Database, and we used single- and multiple-variable analyses to address our research question. In all regions, housing density within protected areas was positively associated with the proportional abundance or proportional richness of synanthropes, and negatively associated with the proportional abundance or proportional richness of Species of Greatest Conservation Need. These relationships were strongest in the eastern forested regions and the central grasslands, where more than 70% and 45%, respectively, of the variation in the proportional abundance of synanthropes and Species of Greatest Conservation Need were explained by housing within protected areas. Furthermore, in most regions, housing density outside protected areas was positively associated with the proportional abundance or proportional richness of synanthropes and negatively associated with the proportional abundance of land cover affiliates and Species of Greatest Conservation Need within protected areas. However, these effects were weaker than housing within protected areas. Natural land cover was high with little variability within protected areas, and consequently, was less influential than housing density within or outside protected areas explaining the proportional abundance or proportional richness of the avian guilds. Our results indicate that housing development within, at the boundary, and outside protected areas impacts avian community structure within protected areas throughout the United States.

Systematic Temporal Patterns in the Relationship Between Housing Development and Forest Bird Biodiversity

As people encroach increasingly on natural areas, one question is how this affects avian biodiversity. The answer to this is partly scale-dependent. At broad scales, human populations and biodiversity concentrate in the same areas and are positively associated, but at local scales people and biodiversity are negatively associated with biodiversity. We investigated whether there is also a systematic temporal trend in the relationship between bird biodiversity and housing development. We used linear regression to examine associations between forest bird species richness and housing growth in the conterminous United States over 30 years. Our data sources were the North American Breeding Bird Survey and the 2000 decennial U.S. Census. In the 9 largest forested ecoregions, housing density increased continually over time. Across the conterminous United States, the association between bird species richness and housing density was positive for virtually all guilds except ground nesting birds. We found a systematic trajectory of declining bird species richness as housing increased through time. In more recently developed ecoregions, where housing density was still low, the association with bird species richness was neutral or positive. In ecoregions that were developed earlier and where housing density was highest, the association of housing density with bird species richness for most guilds was negative and grew stronger with advancing decades. We propose that in general the relationship between human settlement and biodiversity over time unfolds as a 2-phase process. The first phase is apparently innocuous; associations are positive due to coincidence of low-density housing with high biodiversity. The second phase is highly detrimental to biodiversity, and increases in housing density are associated with biodiversity losses. The long-term effect on biodiversity depends on the final housing density. This general pattern can help unify our understanding of the relationship of human encroachment and biodiversity response.

Long‐term avian community response to housing development at the boundary of US protected areas: effect size increases with time

Summary 1. Biodiversity conservation is a primary function of protected areas. However, protected areas also attract people, and therefore, land use has intensified at the boundaries of these lands globally. In the USA, since the 1970s, housing growth at the boundaries (<1 km) of protected areas has increased at a rate far higher than on more distant private lands. Here, we designed our analyses to address our central hypothesis that increasing housing density in and near protected areas will increasingly alter their avian communities. 2. We quantified the relationship between abundance and richness of protected-area avian species of greatest conservation need, land-cover affiliates (e.g. species associated with natural land cover such as forest breeders) and synanthropes (e.g. species associated with humans) with housing density on the boundary of protected areas and on more distant private lands from 1970 to 2010 in three ecoregions of the USA. We accomplished this using linear mixedmodel analyses, data from the US Census Bureau and 90 routes of the North American Breeding Bird Survey. 3. Housing density at the boundary of protected areas tended to be strongly negatively related with the abundance and richness of species of greatest conservation need and landcover affiliates (upwards of 88% of variance explained) and strongly positively related with synanthropes (upwards of 83% of variance explained). The effect size of these relationships increased in most cases from 1970 to 2010 and was greatest in the densely developed eastern forests. In the more sparsely populated West, we found similar, though weaker, associations. 4. Housing density on private lands more distant from protected areas had similar, but more muted negative effects. 5. Synthesis and applications. Our results illustrate that as housing density has increased along the boundary of protected areas, the conservation benefit of these lands has likely diminished. We urge conservation planners to prioritize the purchase of private-land inholdings in order to maximize the extent of unfragmented natural lands within protected areas. Further, we strongly recommend that land-use planners implement boundary management strategies to alter the pattern of human access to protected areas, cluster development to concentrate the footprint of rural housing, and establish conservation agreements through local land trusts to buffer protected areas from the effects of development along protected-area boundaries. To maximize the conservation benefit of protected areas, we suggest that housing development should be restricted within 1 km of their boundaries.

Extreme variations in spring temperature affect ecosystem regulating services provided by birds during migration

Extreme weather is becoming more pronounced, making phenological patterns less predictable. Among the potential consequences, extreme weather may alter relationships of migratory birds with their seasonal food resources and thus impact valuable ecosystem regulating services (e.g., bird predation of herbivorous insects). Our goal was to quantify the effect of an extremely warm spring on these relationships in a U.S Midwest oak savanna. Average regional temperatures in the spring of 2009 coupled with record highs in 2010 (8°C warmer) were the basis of a natural experiment for addressing our goal. In both springs we documented tree flowering and leaf-out phenology, related these to arrival and foraging behavior of the three most abundant migratory wood-warbler species (Parulidae), and quantified the effects of migratory bird foraging on insect density, size, and herbivory using a branch exclosure experiment. In 2009, the dominant tree species at our study site, eastern black oak (Quercus velutina), flowered in mid-May and the wood warblers foraged heavily in the savanna during this time. Branches from which birds were excluded exhibited a trend toward higher insect density, larger Lepidopterans, and greater flower damage than control branches. In 2010, tree phenology was four weeks earlier than in 2009 and the wood warblers were nearly absent from the savanna (83% fewer), likely because peak food availability preceded their arrival in mid-May. Insect density was 83% greater in 2009 than 2010. However, in 2010, 81% of sampled leaves exhibited substantial damage (>25% of leaf-area removed) compared with 27% of leaves in 2009, presumably due to a lack of herbivorous insect regulation by birds. Our results suggest that the extremely warm spring of 2010 altered linkages between migratory birds and their invertebrate prey that are typical during years of average weather, which likely affected habitat use and the delivery of ecosystem regulating services.

Avian Community Use and Occupancy of California Oak Savanna

Abstract. California oak savanna is a habitat of sparse tree canopy that extends from northern Baja California to southern British Columbia and is under threat from land-use pressures such as conversion to agriculture, overgrazing, urban development, and fire suppression. Bird-conservation plans have been drafted for the regions oak woodlands. Yet it is unclear whether birds use California oak savanna at different frequencies than they do neighboring oak habitats. In the foothills of the central and northern Sierra Nevada, California, we explored patterns of avian community structure and habitat occupancy in four habitats: blue oak (Quercus douglasii) savanna with a well-developed grass and forb layer, blue oak savanna with a well-developed shrub layer, and two habitats with a denser canopy, blue oak woodland, and montane hardwood. Additionally, we assessed the effect of habitat characteristics on avian community structure and occupancy. Avian communities were uniquely grouped among the four habitats. Five species of management and conservation concern—the Western Kingbird (Tyrannus verticalis), Western Bluebird (Sialia mexicana), Lark Sparrow (Chondestes grammacus), Western Meadowlark (Sturnella neglecta), and Bullocks Oriole (Icterus bullockii)—were predicted to occupy oak savanna habitats at frequencies higher than in oak woodland or montane hardwood. Shrub cover was the most influential habitat characteristic shaping the avian community and was negatively associated with occupancy of the five savanna-affiliated birds. The distinctive structure and occupancy patterns observed for species of concern in California oak savanna suggest that birds perceive this as unique habitat, highlighting the need for its conservation.