Generating indicator species for bird monitoring within the humid forests of northeast Central America.

The use of indicator species can simplify bird monitoring by reducing the level of specialized skills needed, which increases the potential pool of participants and reduces training costs and complexity. To facilitate monitoring in the humid forests of northeast Central America, we conducted point count surveys for birds across gradients of disturbance in the Cockscomb Basin Wildlife Sanctuary, Belize, and analyzed the association of bird species with remotely sensed metrics of forest condition and anthropogenic disturbance using indicator species analysis. Twenty species exhibited significant associations with one or more of these metrics. We propose six species as indicators for anthropogenic disturbance based on our criteria of being associated with anthropogenically disturbed sites, or anthropogenically disturbed and riparian sites with no explicit mention in the literature of an obligate association with riparian habitats, or association of remotely sensed metrics that appeared to reflect disturbance: yellow-olive flycatcher, red-legged honeycreeper, dusky antbird, blue ground dove, buff-throated saltator, and brown jay. We propose the keel-billed motmot as an indicator of undisturbed forest based on its association with forested sites in our analyses. Green shrike vireo, collard trogon, rufous-tailed jacamar, and rufous piha were associated with a specific elevational range but not associated with disturbance, so upward shifts in elevation that might indicate response to climate change would not be confounded with habitat disturbance or degradation. This exercise yielded a much-reduced list of monitoring targets, which will greatly reduce the cost and complexity of forest bird monitoring in the region, as well as reducing barriers to participation.

Rainfall and habitat interact to affect the condition of a wintering migratory songbird in The Bahamas.

On the subtropical and tropical wintering grounds of migratory birds, variation in moisture levels and habitat can influence the availability of food resources and subsequently impact overwintering birds. Using stable carbon isotopes in blood samples as a measure of moisture, we assessed the interactive effects of rainfall, vegetation, and moisture on the demographics and condition of Prairie Warblers (Setophaga discolor) wintering in The Bahamas. Carbon isotopes in Prairie Warbler blood were more depleted in taller, wetter habitats; we additionally detected novel temporal effects of rainfall on isotope values. During a winter with more rainfall, most birds maintained mass and pectoral muscle regardless of the habitat type occupied. In a winter with less rainfall, birds lost mass and pectoral muscle, and this effect was more pronounced in birds with enriched isotope values and birds that occupied drier, shorter habitat. Prairie Warblers exhibited strong patterns of sexual habitat segregation with males disproportionately observed in areas with taller vegetation and females in shorter vegetation. During the drier winter, older males had better maintenance of pectoral muscle compared to females and younger individuals. Also in the drier winter, daily rainfall patterns explained more of the variation in body condition compared to the date of capture; pectoral muscle was best explained by recent precipitation (during the previous 30 days), while size-corrected mass was more a function of longer-term (90-day) rainfall and habitat moisture. Our findings along with other studies suggest that Prairie Warblers and other migratory birds are sensitive to interactions between annual variation in winter rainfall, within-season daily rainfall patterns, and habitat quality. Increasing drought and habitat loss in the Caribbean may be having a negative impact on wintering bird populations. To best conserve Nearctic-Neotropical migratory passerines in the region, we recommend prioritizing the protection of the least drought-prone wintering areas.

A small-scale land-sparing approach to conserving biological diversity in tropical agricultural landscapes.

Two contrasting strategies have been proposed for conserving biological diversity while meeting the increasing demand for agricultural products: land sparing and land sharing production systems. Land sparing involves increasing yield to reduce the amount of land needed for agriculture, whereas land-sharing agricultural practices incorporate elements of native ecosystems into the production system itself. Although the conservation value of these systems has been extensively debated, empirical studies are lacking. We compared bird communities in shade coffee, a widely practiced land-sharing system in which shade trees are maintained within the coffee plantation, with bird communities in a novel, small-scale, land-sparing coffee-production system (integrated open canopy or IOC coffee) in which farmers obtain higher yields under little or no shade while conserving an area of forest equal to the area under cultivation. Species richness and diversity of forest-dependent birds were higher in the IOC coffee farms than in the shade coffee farms, and community composition was more similar between IOC coffee and primary forest than between shade coffee and primary forest. Our study represents the first empirical comparison of well-defined land sparing and land sharing production systems. Because IOC coffee farms can be established by allowing forest to regenerate on degraded land, widespread adoption of this system could lead to substantial increases in forest cover and carbon sequestration without compromising agricultural yield or threatening the livelihoods of traditional small farmers. However, we studied small farms (<5 ha); thus, our results may not generalize to large-scale land-sharing systems. Furthermore, rather than concluding that land sparing is generally superior to land sharing, we suggest that the optimal approach depends on the crop, local climate, and existing land-use patterns.