Catherine A. Lindell

SURVIVAL, HABITAT USE, AND MOVEMENTS OF FLEDGLING WHITE-THROATED ROBINS (TURDUS ASSIMILIS) IN A COSTA RICAN AGRICULTURAL LANDSCAPE

Abstract We used radiotelemetry to study behavior of White-throated Robins (Turdus assimilis) during the postfledging dependent period. The study was conducted in a mixed agricultural and forested landscape in southern Costa Rica from March through August of 2001 and 2002. A transmitter was attached to one fledgling per brood (n = 53). Each bird was located daily prior to dispersal. We compared survivorship, habitat use, and movements of fledglings from (1) nests in coffee plantations and (2) nests in cattle pastures. The probability of surviving the first three weeks out of the nest was 0.67 ± 0.07 (SE) for fledglings from nests in all habitats, 0.58 ± 0.10 for fledglings from nests in coffee, and 0.74 ± 0.26 for fledglings from nests in pasture. Fledglings from nests in pasture left their nesting habitat at younger ages than did those from nests in coffee, and most birds from both habitats moved into forest when they left their nesting habitat. Pasture was rarely used during the postfledging period, whereas coffee plantations were used extensively. Fledglings that remained in agricultural habitats (coffee or pasture) were less likely to survive until dispersal than were those that moved into forested areas. Average daily distances from the nest gradually increased until fledglings dispersed away from the natal area, always into forest, and were not different for birds from pasture or coffee. White-throated Robins can nest successfully in agricultural habitats, but use of forest positively influenced survivorship of young during the postfledging dependent period.

Factors Influencing Woodpecker Predation on Emerald Ash Borer

ABSTRACT Woodpeckers are a significant source of mortality of emerald ash borer (EAB) (Agrilus planipennis Fairmaire), an Asian phloem-feeding insect first discovered in North America in 2002. However, factors that may influence woodpecker-EAB interactions have not been investigated. We collected data on woodpecker predation, EAB density and tree and site characteristics in southeastern Michigan, where EAB first became established. We tested statistical models to assess the ability of these variables to account for woodpecker predation levels. We observed foraging woodpeckers in the field to determine which species foraged on ash, and to compare the time spent foraging on ash vs. other tree species. Levels of woodpecker predation on EAB were variable, ranging from zero to 26.3 woodpecker attacks per m2 for green ash (n  =  15 sites) and from 2.3 to 37.1 attacks per m2 for white ash (n  =  7 sites). Woodpecker predation level was positively associated with the EAB density in a tree. White ash had higher predation levels than green ash, and less forested sites had higher predation levels than forested sites. However, these variables explained a relatively small amount of the variation in woodpecker predation level. Hairy, downy and red-bellied woodpeckers were observed foraging on ash trees. Woodpeckers spent significantly more time in foraging bouts on ash than on other tree species in EAB-infested areas. We suggest that managers of sites with substantial ash populations maintain conditions that are attractive to woodpeckers to encourage predation of EAB. Our analyses indicate that we need to understand much more about the foraging patterns of woodpeckers on EAB to be able to predict their impact on EAB populations.

Characteristics of bird species using forest and agricultural land covers in southern Costa Rica

Our understanding of why tropical forest species differ in their ability to inhabit agroecosystems is limited, despite the link between this ability and the likelihood of population decline for species inhabiting regions undergoing widespread conversion of forest to agriculture. We used logistic regression and data from southern Costa Rica to develop a model based on natural history characteristics to distinguish between forest species that did or did not use agricultural land covers. We sampled birds along 15 3.0-km routes, seven in forest and eight in agriculture, five times over three years. Each species was classified as an F-species, detected only in forest, a G-species, detected in both forest and agriculture, or an A-species, detected only in agriculture. Thirty percent of species were F-species, 42% were G-species, and 28% were A-species. Based on the logistic regression model, the likelihood of being a G-species, as opposed to an F-species, was low for species that were dependent on forest interior, had a stenophagous diet, and a small elevational range. Weight, resident versus migrant status, and whether or not a species was insectivorous, were not significant predictors of being a G-species. For all F–G species pairs, the model correctly predicted the G-species 70% of the time. The model provides a first step in identifying those characteristics that predispose forest species to use agricultural land. In addition, our results indicate that the structurally simple agricultural systems of the study region are of limited value for a large proportion of the regional species pool.

Patterns of nest usurpation: When should species converge on nest niches?

The acceptability of a nest to more than one species and the convergence of species on a nest niche is demonstrated through nest usurpation. I compiled examples of nest usurpation from the literature to examine patterns regarding the species and nest sites that tend to be usurped, those species likely to be usurpers, and the habitats in which usurpation occurs. Cavities and enclosed nests are more likely to be usurped than cup nests. Species that excavate or build these types of nests, like the Picidae and the Furnariidae, are likely to be the hosts of usurpers. Particular groups are prone to usurping nests, including introduced species like the House Sparrow (Passer domesticus) and European Starling (Sturnus vulgaris). Cavity usurpations were more likely to be observed in temperate than tropical/subtropical zones, and about equally likely to be observed in closed and open habitats, while enclosed nest usurpations were observed more frequently in open than closed habitats, and more often in tropical/subtropical than temperate zones. Usurpation of all nest types is more likely to occur in tropical/subtropical zones than expected, based on the number of studies in the literature conducted in these zones. Usurpation of all nest types is less likely to occur in open, and more likely to occur in moderately open habitats than expected, based on the number of studies in the literature conducted in these habitats. Instances of cavity usurpation, recorded primarily in temperate zones, across a variety of habitats, do not contribute to these general patterns. Nest-site convergence through nest usurpation may be more likely to occur in moderately open tropical habitats because of : 1) the availability of enclosed nests, 2) the limited structural heterogeneity of the vegetation, which limits the possibility of nest-niche partitioning, and 3) the high diversity of potential nest competitors and predators. In such environments, interspecific nesting associations may be a more effective generalized nest defense strategy than using a nest site that is difficult to find.

Bird and bat predation services in tropical forests and agroforestry landscapes

Understanding distribution patterns and multitrophic interactions is critical for managing bat‐ and bird‐mediated ecosystem services such as the suppression of pest and non‐pest arthropods. Despite the ecological and economic importance of bats and birds in tropical forests, agroforestry systems, and agricultural systems mixed with natural forest, a systematic review of their impact is still missing. A growing number of bird and bat exclosure experiments has improved our knowledge allowing new conclusions regarding their roles in food webs and associated ecosystem services. Here, we review the distribution patterns of insectivorous birds and bats, their local and landscape drivers, and their effects on trophic cascades in tropical ecosystems. We report that for birds but not bats community composition and relative importance of functional groups changes conspicuously from forests to habitats including both agricultural areas and forests, here termed ‘forest‐agri’ habitats, with reduced representation of insectivores in the latter. In contrast to previous theory regarding trophic cascade strength, we find that birds and bats reduce the density and biomass of arthropods in the tropics with effect sizes similar to those in temperate and boreal communities. The relative importance of birds versus bats in regulating pest abundances varies with season, geography and management. Birds and bats may even suppress tropical arthropod outbreaks, although positive effects on plant growth are not always reported. As both bats and birds are major agents of pest suppression, a better understanding of the local and landscape factors driving the variability of their impact is needed.

Birds and bats reduce insect biomass and leaf damage in tropical forest restoration sites

Both birds and bats are important insect predators in tropical systems. However, the relative influence of birds and bats on insect populations and their indirect effects on leaf damage have not previously been investigated in tropical forest restoration sites. Leaf damage by herbivorous insects can negatively affect the growth and survival of tropical plants and thus can influence the success of tropical forest restoration efforts. We used an exclosure experiment to examine the top-down effects of birds and bats on insects and leaf damage in a large-scale forest restoration experiment. Given the potential influence of tree planting design on bird and bat abundances, we also investigated planting design effects on bird and bat insectivory and leaf damage. The experiment included two planting treatment plots: islands, where trees were planted in patches, and plantations, where trees were planted in rows to create continuous cover. In both types of plots, insect biomass was highest on tree branches where both birds and bats were excluded from foraging and lowest on branches without exclosures where both birds and bats were present. In the island plots, birds and bats had approximately equal impacts on insect populations, while in plantations bats appeared to have a slightly stronger effect on insects than did birds. In plantations, the levels of leaf damage were higher on branches where birds and bats were excluded than on branches where both had access. In island plots, no significant differences in leaf damage were found between exclosure treatments although potential patterns were in the same direction as in the plantations. Our results suggest that both birds and bats play important roles as top predators in restoration systems by reducing herbivorous insects and their damage to planted trees. Tropical restoration projects should include efforts to attract and provide suitable habitat for birds and bats, given their demonstrated ecological importance.

EGG TYPE INFLUENCES PREDATION RATES IN ARTIFICIAL NEST EXPERIMENT

Abstract Egg type is one factor that is likely to influence the results from artificial nest experiments. Here I document predation rates on Japanese Quail (Coturnix japonica) and the much smaller Zebra Finch (Taeniopygia guttata) eggs on the edge and interior of a tropical forest in Costa Rica. Predation rates on finch eggs were the same on the edge and in the interior of the forest (60.9 and 60.0%, respectively), while predation rates on quail eggs were significantly different on the edge and in the interior (76.5 and 35.0%, respectively). Hence, results from artificial nest experiments may be highly dependent on the type of egg used and caution is advised in their interpretation.

Nesting bird species in sun coffee, pasture, and understory forest in southern Costa Rica

We investigated avian nest distribution and success in understoryforest, sun coffee plantations, and pasture in southern Costa Rica. Nestsearching occurred in plantations and forest in 1999 and 2000 and in pastures in2000. Nests were monitored until they failed or fledged young. Antbirds(Thamnophilidae) were the most common understory forest nesters and were notfound nesting in the plantations or pastures. Common nesting species in theplantations included Turdidae, Tyrannidae, Cardinalidae, and Thraupidae, many ofwhich are typical of forest edge/canopy or open, scrubby habitats. Two speciesassociated with forest interior, Henicorhina leucostictaand Buarremon brunneinucha, were found nesting in theplantations. Pastures supported similar types of nesting species as theplantations, with the exception of the forest-interior species. Daily mortalityrates (DMRs) for above-ground cup-nesting species in plantations and pastureswere similar to those for species nesting in forest at our site and a site inPanama. The results indicate that conversion from forest to pastures and suncoffee plantations diminishes nesting habitat for forest-interior species, whilenumerous forest edge/canopy species and open-country species are able to nest inthese agricultural land-cover types. As a group, species nesting in theplantations and pastures do not have unusually high nest mortality rates,although species-specific studies are lacking. Nesting species distributionsacross habitat types and DMRs at our study site may be influenced by the largeamount of forest in the landscape.

Migratory bird species in young tropical forest restoration sites: effects of vegetation height, planting design, and season

Summary Tropical land cover change has negatively affected numerous migratory bird populations. Forest restoration can augment migrant wintering habitat. However, almost no information exists about factors that influence migrant use of tropical restoration sites. We sampled migrant birds in young restoration sites in Costa Rica from February 2006 to April 2008 to determine how vegetation height, planting design, season, and landscape forest cover influenced capture rates of four declining species. We also documented total numbers of migratory species and individuals captured in each planting design treatment; each site had a control treatment where seedlings were not planted, an island treatment where seedlings were planted in patches, and a plantation treatment where seedlings were planted to cover the entire area. Sites varied in landscape forest cover within 500 m buffers. Three out of four focal species were captured significantly more often in plantation treatments than island or control treatments. Two of the four species showed seasonal patterns and one species was captured more often in high-vegetation sites. Greater numbers of species and individuals were captured in plantation treatments compared to island and control treatments. The plantation planting design increased migrant use more quickly than the island planting design. When resources are available, we recommend planting plantation-style to rapidly increase the value of restoration sites to a range of species, particularly those that use woody vegetation. When resources are more limited, planting islands may be a cost-effective, although not as ecologically effective, alternative that supports a diversity of migrant species compared to unplanted controls.

Habitat use of adult White-throated Robins during the breeding season in a mosaic landscape in Costa Rica

Abstract Most work on the effects of land-cover change on tropical birds has focused on forest-interior birds because these species are assumed to be the most severely affected by forest loss. However, even species that use human-altered habitat types may be severely affected by forest loss. White-throated Robins (Turdus assimilis) frequently nest in coffee and pasture in southern Costa Rica, although several lines of evidence suggest the species could not exist solely in agricultural habitat. We used radio-telemetry to examine the area and proportion of different habitat types used by adult White-throated Robins. Mean area of use for the tracking period was 0.26 km2 and varied from 0.07 to 0.58 km2. No robins had areas of use solely in either primary forest or agricultural cover, although individuals were initially captured in both primary forest and a coffee plantation. All areas of use contained some forest, pasture, and coffee or regenerating forest. The mean percentages of the habitat types used by the birds were fairly equal with 30% forest, 33% pasture, and 38% coffee or regenerating forest. Our results, combined with other evidence, indicate that the White-throated Robin uses multiple habitat types but that it may require some threshold level of forest to sustain viable populations.