Associations Between Avian Spruce-fir Species, Harvest Treatments, Vegetation, and Edges

Habitat loss is the primary cause of species loss and declines of global biodiversity. Several birds associated with the spruce-fir forest type (hereafter spruce-fir birds) have declining populations across the continent in the Atlantic Northern Forest, and the extent of coniferous forest has declined in some areas. This region is extensively and intensively managed for timber products. To investigate the influence from harvest treatments on the spruce-fir bird assemblage during the breeding and post-breeding period in lowland conifer and mixed-wood forests, we used avian point count detection data to test for associations between avian assemblages and seven common harvest treatments. Spruce-fir avian assemblages had greatest abundance in regenerating clearcuts combined with postharvest treatments (i.e., herbicide and precommercial thinning), and within stands having ≥60% spruce-fir tree composition. Richness of spruce-fir avian assemblages were greatest in stands with immature trees and greater spruce-fir tree composition, and clearcuts combined with postharvest treatments had greater spruce-fir tree composition compared to other treatments. Next, we tested for effects from management, years-since-harvest, and vegetation on abundance of 19 conifer associated avian focal species while accounting for the effects from detection probability. Abundance of six species differed significantly among harvest treatments, and one species was associated with years-since-harvest, indicating that management treatments provided important information. In addition, fourteen species had significant associations between abundance and vegetation variables, suggesting that managers could target specific vegetative outcomes when managing for focal species. We tested for differences in avian abundance and richness at stand interior ≥80 m from edges, low-contrast edges at the junction of two regenerating stands, and high-contrast road edges with managed buffers using a novel multi-species abundance model. Spruce-fir birds had greater richness at stand interior compared to high-contrast edge, and stand interior had greater spruce-fir tree composition compared to high-contrast edge, while low-contrast edge was intermediate. Road edges reduced habitat for spruce-fir birds. Combined our results suggest that management could promote habitat for spruce-fir birds through: 1) application of postharvest treatments such as herbicide and precommercial thinning; 2) using management that targets focal species by using outcome-based silviculture; 3) minimizing access road edges and roadside buffers

Predicting Occupancy of Wintering Migratory Birds: Is Microhabitat Information Necessary?

Information regarding microhabitat, here defined as small-scale vegetation structure, is often useful in predicting use of habitat by birds. Quantifying microhabitat, however, is expensive and labor intensive compared to assessment of habitat at a larger scale, possibly from remotely sensed imagery. To assess the importance of microhabitat information in constructing predictive models of habitat occupancy, we compared occupancy models built on the basis of macro- and microhabitat together and separately. We based our models on counts of wintering migratory bird species and vegetation surveys within Tuskegee National Forest, Alabama, completed during winter 2009. Models built from macrohabitat data only outperformed models built from microhabitat data only for five of the six species analyzed. However, the best model for every focal species included both macro- and microhabitat covariates. Pine forests—excluding plantation—were the only land-cover classification important to our focal species, and measures of density of vegetation were important in predicting occupancy. Our results suggest that migrants wintering at our study site select habitat at multiple scales—specializing in certain types of cover and then preferring specific structural aspects of vegetation within them. We conclude that microhabitat information is important for inference into use of habitat by wintering migratory birds

Evidence Suggesting that Ivory-billed Woodpeckers (Campephilus principalis) Exist in Florida

The Ivory-billed Woodpecker (Campephilus principalis) disappeared from the forests of southeastern North America in the early 20th Century and for more than 50 years has been widely considered extinct. On 21 May 2005, we detected a bird that we identified as an Ivory-billed Woodpecker in the mature swamp forest along the Choctawhatchee River in the panhandle of Florida. During a subsequent year of research, members of our small search team observed birds that we identified as Ivory-billed Woodpeckers on 14 occasions. We heard sounds that matched descriptions of Ivory-billed Woodpecker acoustic signals on 41 occasions. We recorded 99 putative double knocks and 210 putative kent calls. We located cavities in the size range reported for Ivory-billed Woodpeckers and larger than those of Pileated Woodpeckers (Dryocopus pileatus) that have been reported in the literature or that we measured in Alabama. We documented unique foraging signs consistent with the feeding behavior of Ivory-billed Woodpeckers. Our evidence suggests that Ivory-billed Woodpeckers may be present in the forests along the Choctawhatchee River and warrants an expanded search of this bottomland forest habitat

Pitfalls arising from site selection bias in population monitoring defy simple heuristics

Abstract Site selection bias can occur when researchers monitor animals at sites of great abundance, occupancy or quality. The prevailing heuristic is therefore that ecologists should never select sites using these criteria. There is thus concern that common monitoring schemes including surveys at colonies, migratory bottlenecks and artificial breeding sites intentionally monitor sites of great abundance. Whether such routine monitoring schemes likely succumb to site selection bias is unexamined. We simulate the dynamics of long‐lived vertebrate populations to test three potential pitfalls hypothesized to occur when sites are selected for monitoring based on abundance, occupancy or quality. (1) For regression to the mean, population levels might appear to decline at monitored sites because they were chosen during a peak of abundance and random fluctuations cause populations to decrease from that point. (2) Preferential sampling occurs when some sites are preferred by the focal organism and have an above‐average probability of being selected for monitoring. (3) The missing zero effect occurs when occupied sites are chosen more often for monitoring because of initial or historical occupancy. Our simulations demonstrate that regression to the mean should only occur when inter‐annual fluctuations in abundance are relatively large compared with the average difference between sites. If researchers monitor sites that are truly of great average abundance, regression to the mean is avoided. Preferential sampling can cause a delay in the detection of a decline because monitored sites are preferred by the focal species and thus should be the first to be occupied and the last to be abandoned. Finally, the missing zero effect can cause a perceived decline in a stable population because sites were chosen when they were initially occupied and thus can only be abandoned, whereas potential colonizations at initially unoccupied sites cannot be observed. Regression to the mean occurred during specific circumstances that do not seem biologically plausible for some study systems (e.g. colony surveys). It is therefore impractical to apply a single simple heuristic such as ‘never monitor animals at sites of great abundance’ across organisms of varying life histories

Seasonal Use of Habitat by Shrub-Breeding Birds in a Southeastern National Forest

Populations of shrub-breeding birds are declining in eastern North America, and loss of habitat has been implicated in these declines. Seasonal use of habitat by shrub-breeding birds in the southeastern US remains understudied despite the fact that it is well documented that species resident within a region can shift habitat use dramatically between seasons. To better understand year-round habitat occupancy by shrub-breeding birds, we conducted bird counts and vegetation surveys during summer and winter 2008–2009 within Tuskegee National Forest, Alabama. We used multi-season occupancy models to examine use of habitat and to contrast seasonal occupancy patterns of four species of resident shrub-breeding birds—Brown Thrashers (Toxostoma rufum), Eastern Towhees (Pipilo erythrophthalmus), Northern Cardinals (Cardinalis cardinalis) and Carolina Wrens (Thryothorus ludovicianus). Brown Thrashers and Eastern Towhees are partially migratory—meaning some populations have separate breeding and wintering areas—whereas Carolina Wrens and Northern Cardinals are non-migratory. All four species showed seasonal changes in use of habitat between summer and winter, and all species were associated with both vegetation structure and certain types of cover. Further, partially migratory shrub-breeding species had greater site-turnover and increases in occupancy between summer and winter than non-migratory species. Our results suggest that: (1) management actions based on breeding habitat requirements will likely not create suitable winter habitat, and (2) management of resident shrub-breeding birds will require not only the creation and maintenance of certain types of cover, but also certain structural aspects of vegetation within habitats

Risk from cattle trampling to nests of an endangered passerine evaluated using artificial nest experiments and simulations

Grasslands are often grazed by cattle and many grassland birds nest on the ground, potentially exposing nests to trampling. We tested for trampling risk introduced by cattle to nests of endangered Florida Grasshopper Sparrows (Ammodramus savannarum floridanus) using experimentally paired grids of artificial nests (i.e., clay targets) similar in size to nests of Florida Grasshopper Sparrows and counted the number of clay targets that were broken in paired grazed and ungrazed enclosures. Clay targets in grazed grids were trampled 3.9% more often than their respective ungrazed grids, and measurements of cattle presence or density were correlated with the number of broken clay targets, suggesting that excluding cattle during breeding is an important management recommendation for the Florida Grasshopper Sparrow. Trampling rates within grazed enclosures were spatially homogeneous with respect to cattle infrastructure such as supplemental feeding troughs and fences, and forests and stocking density were poor predictors of trampling rates when excluding ungrazed grids. We used population viability analysis to compare quasi-extinction rates, intrinsic growth rates, and median abundance in grazed and ungrazed Florida Grasshopper Sparrow aggregations to further understand the biological significance of management aimed at reducing trampling rates during the breeding season. Simulations indicated that trampling from grazing increased quasi-extinction rates by 41% while reducing intrinsic growth rates by 0.048, and reducing median abundance by an average of 214 singing males after 50 years. Management should avoid grazing enclosures occupied by Florida Grasshopper Sparrows during the nesting season to minimize trampling rates. Our methods that combine trampling experiments with population viability analysis provide a framework for testing effects from trampling on other grassland ground-nesting birds, and can directly inform conservation and management of the Florida Grasshopper Sparrow

Accounting for misclassification of subspecies provides insights about habitat use and dynamics of the Florida Grasshopper Sparrow in response to fire

Monitoring populations is critical to understanding habitat use, especially for endangered species and is important for determining the effectiveness of land management strategies. The Florida Grasshopper Sparrow ( Ammodramus savannarum floridanus ) is a critically endangered non-migratory grassland bird that has been monitored since the 1990s. It resides primarily in dry prairie habitat managed by frequent (2–3 years) prescribed fires. Monitoring is confounded by the presence of the migratory and wintering eastern Grasshopper Sparrow ( A. s. pratensis ), that has vocal and morphological similarities. These similarities could lead to misclassifications and erroneous conclusions about land management. Our goal was to determine the impact of fires on Florida Grasshopper Sparrow habitat use at two spatial scales, 100 m and 400 m buffers surrounding point count locations, while controlling for the presence of the eastern Grasshopper Sparrow. We combined point count data (1996–2011), external sources of data (eBird), and Bayesian dynamic occupancy models that accounted for misclassifications to evaluate habitat use and dynamics in response to prescribed fires. The probability of misclassifying a Florida Grasshopper Sparrow peaked in April and then decreased to near zero after May 1. The probability of persistence at point count stations decreased as years-since-fire (maximum of pixels within 400 m buffer) increased and was greatest for recent burns (< 1 year). Seasonality of the most recent burn (i.e., ordinal date of burn for pixels within 100 m buffer) also influenced probability of persistence with Florida Grasshopper Sparrows having greater-than-average persistence when burns occurred during January and July, peaking in early April. The probability of colonization peaked approximately two months after a fire and rapidly decreased to negligible values. This is the first long-term study to examine the effect of prescribed burn on Florida Grasshopper Sparrow occupancy that accounts for the presence of eastern Grasshopper Sparrows. This modeling framework may also provide utility for other species and subspecies that are difficult to distinguish during surveys