Conservation of Neotropical migratory birds in tropical hardwood and oil palm plantations

Abstract

Tropical forests in the Americas are undergoing rapid conversion to commercial agriculture, and many migratory bird species that use these forests have experienced corresponding populations declines. Conservation research for migratory birds in the tropics has focused overwhelmingly on shade coffee plantations and adjacent forest, but both cover types are now in decline, creating an urgent need to evaluate conservation opportunities in other agricultural systems. Here we compare how a community of 42 Neotropical migratory bird species and a subset of five conservation-priority species differ in usage and habitat associations among a secondary forest baseline and four expanding commercial plantation systems in Guatemala: African oil palm, teak, rubber, and mixed-native hardwoods. We found that mixed-native hardwood plantations supported the highest richness and diversity of all migrants and that the three hardwood plantation types generally outperformed oil palm in richness and diversity metrics. Despite this, oil palm supported high abundance of several common and widespread species also experiencing range-wide population declines and may therefore play an important role in conserving common species. Mature secondary forest hosted low abundance and diversity of the full migratory community, but high abundance and richness of conservation priority migrants along with native hardwood and teak plantations. Likewise, the percentage of forest cover on the landscape was positively associated with priority migrant abundance and richness but negatively associated with the abundance of migrants in general, highlighting how individual species within the broad group of Neotropical migratory landbirds respond differently to anthropogenic changes in land use. Across all cover types, the retention of tall overstory trees increased the abundance, richness, and diversity of all migrants, which indicates that vertical structural diversity and remnant trees are important habitat features for birds in agricultural landscapes. Our findings show that conservation opportunities exist in hardwood and oil palm plantations, though the species likely to benefit from conservation action will vary among plantation types. For the subset of conservation priority migrants, our results suggest that conservation efforts should combine strategies that retain and restore secondary forest, promote the adoption of native hardwood and teak plantations, and promote the retention of tall, remnant trees in agricultural landscapes.

Migratory bird community structure in oil palm (Elaies guineensis) plantations and native forest fragments in southern Mexico

“…Our results suggest that, although species richness of migratory birds in native forest and oil palm plantations did not differ significantly, the community assemblages of migrant birds differed significantly between the two habitats. These results partially corroborate the findings of Bennett et al (2018) in Guatemala, where species richness and diversity of migratory birds were similar in oil palm and secondary forest. The community assemblage in native forest was characterized by species with narrower habitat tolerances and less plasticity in habitat use and foraging behavior (e.g., Kentucky Warblers, Worm‐eating Warblers, Wood Thrushes, Blue‐winged Warblers, and Swainson's Warblers) (Forbush 1929, Ficken and Ficken 1968, Lack and Lack 1972, Greenberg 1987, Holmes and Robinson 1988, Graves 1998).…”

“…Within this radius, we measured six structural features: (1) diameter at breast height (DBH; we only considered trees with DBH ≥ 10 cm), (2) tree density, (3) tree species richness, (4) tree height, (5) understory density, and (6) canopy cover. Variables were chosen based on the results of previous studies relating bird communities with vegetation complexity in plantations (Greenberg et al 1997, 2000, Philpott et al 2008, Bakermans et al 2012, Bennet et al 2018, Colorado et al 2018). Tree height was measured using an electronic clinometer.…”

“…The secondary matrix for each ordination contained a categorical variable for habitat type. We included “tallest tree” in the vegetative structure PCA based on recommendations from Bennet et al (2018), where the tallest tree was found to be an important predictor of migratory bird abundance, richness, and diversity. Prior to our ordination analysis, we used ANOVA to assess homogeneity of multivariate dispersion (Anderson 2005).…”

“…Few investigators have examined the use of oil palm plantations by migrant birds in the Neotropics. In Guatemala, Bennet et al (2018) compared migratory bird communities in oil palm and secondary forest and found a similar species richness, but a greater abundance of migratory birds in oil palm than in secondary forest. Conversely, in Tabasco, Mexico, Moo‐Culebro (2018) found greater species richness of migratory birds in oil palm than in secondary forest and pasture.…”

Annual temperature variation influences the vulnerability of montane bird communities to land‐use change

“…We contrasted the proportion of forest use by region across all species, but to ensure our results were not influenced by differences in species' natural histories, we also contrasted the proportion of forest use within foraging guilds and by migratory strategy, two ecological traits that are generally thought to be associated with sensitivity to forest loss (Newbold et al 2013). For example, forest conversion and fragmentation are thought to particularly affect insectivorous birds (Şekercioḡlu et al 2002) and to reduce nesting success in long-distance migratory birds (Robinson et al 1995), but forests that have been converted to some types of agriculture can retain a substantial number of migrant species on winter territories (Bennett et al 2018). We assigned each species in each region to a primary foraging guild and to a migratory strategy following Grimmett et al (1999) (Supplementary material Appendix 1 Table A1).…”