DOI: 10.5061/dryad.b8gtht7fj
title: Data for: Avian use of avocado farms and intact forest in the northern Sierra de Bahoruco, Dominican Repebulic

description: The Dominican Republic is experiencing increased forest loss due to the
 expansion of avocado farming. While agricultural lands can provide viable
 habitat for birds, knowledge of avian use of avocado farms relative to
 native forest is limited. We conducted surveys in fall 2021 to compare the
 bird communities and vegetation complexity of two avocado farm sites and
 two native dry forest sites in the northern Sierra de Bahoruco region of
 the Dominican Republic to assess avian habitat use. Overall, we found that
 habitat associations differed for bird species distinguished by
 contrasting geographic ranges. In particular, the abundance, richness, and
 diversity of bird species endemic to Hispaniola were significantly greater
 in forests than in farms, while non-endemic resident bird species had the
 opposite habitat associations. The abundance, richness, and diversity of
 Neotropical migrants exhibited fewer distinct differences between farm and
 forest sites. Vegetation structural complexity was reduced in avocado
 farms relative to forests and was positively associated with the
 abundance, richness, and diversity of endemic bird species but negatively
 associated with these community measures of non-endemic resident species.
 Collectively, our findings suggest that avocado farms could provide viable
 habitat for non-endemic resident and migrant bird species, but that
 endemic species could be negatively impacted by an increase in avocado
 farming in the region. We offer recommendations for forest preservation,
 farming practices, and future research that could help to inform the
 conservation of endemic species in the region.
description: <strong>Study Sites</strong><br>The study area
 is located near the town of Puerto Escondido, Independéncia Province, in
 the foothills of the northern Sierra de Bahoruco in the southwestern
 Dominican Republic. Natural forests in this area are considered
 subtropical dry forests (Knudson et al. 1988) with elevations ranging from
 421 to 522 m. Dominant vegetation in the region includes large trees such
 as baitoa (<em>Phyllostylon brasiliensis</em>), candelón
 (<em>Acacia scleroxyla</em>), and guayacán (<em>Guaiacum
 officinale</em>) and understory shrubs such as escobón
 (<em>Eugenia monticola</em>) and grenadilla (<em>Eugenia
 ligustrina</em>). The town of Puerto Escondido is situated near
 multiple limestone water outlets, providing water for community needs and
 agricultural irrigation. We conducted field work in four study sites
 within the area: two native forest sites and two avocado farm sites.
 Avocado farms of two sizes were chosen for the comparison to reflect the
 variety of such farms in the region, including potential differences in
 vegetation complexity. Specifically, we chose one farm site comprised of
 multiple, relatively small community parcelas; this is land near town that
 is divided into adjacent plots, each with a single owner who primarily
 cultivates one crop. All parcelas cultivating avocados were included in
 the small farm study site, which was located within 2 km of native dry
 forest dry forest along a portion of a well-known birding trail called
 Rabo de Gato (Figure 1). The other forest site was located in Reserva Loma
 Charco Azul, a federally protected 17,400-ha dry forest reserve (Figure
 1), known for being the main habitat of the endemic Bay breasted Cuckoo. A
 second farm site was located in a large organic commercial farm
 characterized by groves of primarily Hass and Carla avocados. Due to
 restricted permissions by the landowner, we are unable to disclose the
 specific location of our large farm site. Both avocado farm sites border
 native forest, which minimized potential differences in climate,
 topography, and human disturbance as a result of proximity to
 town.<br><br><strong>Bird Community
 Surveys</strong><br>We used point-count surveys (Wunderle and
 Waide 1993, Wunderle and Latta 1996, Greenberg et al. 2000, Marsden et al.
 2001, Latta et al. 2003, Kennedy et al. 2010) to assess overall, endemic,
 and migrant bird communities in the study sites. We designated survey
 points using a grid system in which all points were at least 150 m apart
 to reduce the possibility of double-counting individual birds. We also
 ensured that all points were greater than 25 m away from the boundary of
 the site so that only species within the site were detected during
 surveying. The size and elevation of our study sites and the number of
 survey points in each site are listed in Table 1. We conducted point count
 surveys from October 13 to December 1, 2021, to include overwintering
 migrant species. We visited each point three times during the field
 season, and alternated between forest and farm point counts on consecutive
 days to account for differences due to the effects of weather or other
 short-term temporal events. We began surveys at sunrise and ended no later
 than four hours after sunrise, encompassing the period when birds are most
 active and likely to be detected. We recorded all birds seen and/or heard
 within 25 m of each point for a 10-minute period. Using relatively small
 point-count radius ensured that we were recording bird species within the
 habitat type we were surveying, which was especially critical in smaller
 avocado farms. Birds that flushed upon arrival were included in the point
 count, but birds flying over without stopping in the site were not
 counted. We averaged the number of individual birds and species across the
 three survey dates at each point. To investigate habitat use by non-
 endemic resident, endemic, and Neotropical migrant species, in particular,
 we similarly calculated the mean number of individuals and bird species
 within each group per survey point. Endemic bird species were defined as
 those only found in Hispaniola and its satellite islands (Latta et al.
 2006), and migrant bird species were defined as those that breed north of
 the Tropic of Capricorn but winter south of this location (Hagan and
 Johnston 1992). We used the term ‘non-endemic resident’ to describe more
 geographically widespread, non-migratory species observed in our study
 sites. To characterize the diversity of the non-endemic
 resident, endemic, and migrant bird communities in each study site, we
 calculated the frequency of each species identified as the percentage of
 the total bird survey points in each site in which that species was
 observed across all three site visits. We used the Shannon Diversity Index
 (Shannon 1948) to calculate the diversity of the overall, non-endemic
 resident, migrant, and endemic bird communities in each site during each
 visit. We averaged the diversity scores of the three visits to calculate a
 mean diversity measure per point. Bird survey details, including the
 distance that birds were identified from survey points, method of
 detection, weather variables, and ambient noise are provided in a
 supplementary dataset.<br><br><strong>Vegetation
 Complexity Measures</strong><br>We assessed canopy cover,
 canopy height, and canopy thickness at each bird survey point and at four
 additional subpoints, one in each cardinal direction 25 m from the main
 survey point (see Van Bael et al. 2007). Canopy cover was estimated by
 using a tube densiometer at each survey point and subpoint. To determine
 canopy height and canopy thickness, we used a digital rangefinder to
 measure height of the highest and lowest foliage associated with trees at
 each survey point and subpoint. Canopy thickness was calculated as the
 upper height minus the lower height at each measurement location (see Muth
 and Bazzaz et al. 2002, Mas and Dietsch 2004, Lee et al. 2020). ​​We
 averaged the vegetation data collected at each survey point and its
 subpoints to calculate the mean canopy cover, canopy height, and canopy
 thickness for each survey point. To assess the diversity of vegetation in
 each study site, we identified the five most dominant woody species
 greater than 1-m tall in a 25-m-radius circle around each bird survey
 point and visually estimated the percent cover of each of these species
 (see McClaren et al. 2019). The five woody plant species with the highest
 vegetative cover within the circle were identified as dominant species at
 that point. For cultivated crops, we included horticultural varieties as
 ‘species’ in our analyses given that horticultural vareties are selected
 for distinct differences in traits that could potentially impact habitat
 preference, including leaf shape and size and fruiting phenology. To
 characterize the diversity of the vegetation in each study site, we
 calculated the frequency of each dominant plant species as the percentage
 of the total survey circles in each site in which that species was
 observed across all three site visits.
 <strong>Statistical Analyses</strong><br>We
 tested for the normality of our data distribution within groups (i.e.,
 sites) with Shapiro-Wilk test and for homogeneity of variances with
 Levene’s tests. When the assumptions of normality and homogeneity of
 variances were both met, we used a one-way ANOVA to test for the effect of
 site on vegetation complexity (i.e., canopy height, canopy cover, canopy
 thickness) and bird community measures (i.e., number of individuals,
 species richness, species diversity) followed by least-significant
 difference LSD post-hoc tests when the effect was significant. When the
 assumption of normality was met but variances were not homogenous, we used
 Welch’s ANOVA followed by Games-Howell post-hoc tests when the effect was
 significant. When the assumption of normality was not met but variances
 were homogenous, we used non-parametric Kruskal-Wallis tests to test for
 the main effect of site followed by Dunn-Bonferroni post-hoc tests when
 the effect was significant. In all cases, differences in mean values were
 considered significant if p is less than or equal to 0.05. To examine
 associations between vegetation complexity and bird community measures, we
 performed linear regression analyses in SPSS. To account for the numerous
 associations analyzed, we calculated and utilized corrected p-values to
 control the false discovery rate for the group of tests for each bird
 community type (i.e., non-endemic resident, endemic, migrant) in
 accordance with methods described by Benjamini and Hochberg (1995).
 Results of regression analyses were considered significant if
 FDR-corrected p is less than or equal to 0.05. All data analyses were
 conducted with SPSS (version 29, IBM Corp., Armonk, New York,
 USA).