DOI: 10.5061/dryad.1c59zw3tn
title: Hornbill abundance and breeding incidence in relation to habitat modification and fig fruit availability

description: Asian hornbills are known to forage and breed in fragmented rainforests
 and agroforestry plantations in human‐modified landscapes adjoining
 contiguous protected forests. However, the factors influencing year‐round
 hornbill abundance, demography and tracking of key food resources such as
 wild fig Ficus fruits in modified habitats and protected forests remain
 poorly understood. We carried out monthly surveys of two species of high
 conservation concern, the Vulnerable Great Hornbill (GH, Buceros bicornis)
 and the endemic Malabar Grey Hornbill (MGH, Ocyceros griseus) for 15
 months and monitored ripe fig fruit availability for 12 months along 11
 line transects (total length 24 km) in shade‐coffee plantations and
 adjoining continuous rainforests in a protected area (PA) in the Anamalai
 Hills, Western Ghats, India. Both hornbill species used plantations and
 the PA year‐round but distance sampling density estimates were higher in
 the PA in both nesting (GH by 57%; MGH by 50%) and non‐nesting (GH by 53%;
 MGH by 144%) seasons. Relative to estimates from 2004 to 2005, mean GH
 density appeared stable or increasing, whereas MGH had declined by 39% in
 the PA and by 56% in plantations. Monthly encounter rate of both hornbills
 tended to be higher in the PA and that of MGH was also positively related
 to the density of fig trees with ripe fruit. Sex ratios of observed adult
 birds in the non‐nesting season were relatively even (GH) or slightly
 female‐biased (MGH), but became male‐biased in both species during the
 nesting season when females were confined in tree‐cavity nests. We used
 change in the adult sex ratio of observed birds from the non‐nesting to
 nesting season to estimate an index of the proportion of adult pairs
 breeding at any point within the season, providing the first such
 estimates for any hornbill species. The proportion of breeding pairs was
 higher in the PA (GH – 56%, MGH – 64%) than in the plantations (GH – 33%,
 MGH – 30%). Although hornbills use shade‐coffee plantations year‐round,
 partly due to fig fruit availability, differences in hornbill density and
 breeding incidence, as assessed from the sex ratios of observed adult
 birds, indicate that plantations are a sub‐optimal habitat for both
 species.
description: The data were collected as described in Pawar et al.
 (2020), <em>Ibis
 </em>(https://doi.org/10.1111/ibi.12895). This includes hornbill
 observations data from 11 line transects from the protected area (PA) and
 plantations (see file: Sites.csv). It includes fig phenology monitoring
 data from belt transect surveys as described in the publication.
description: The 01_ReadMe.txt file contains details of each column of data in
 the following files that are included in the dataset.
 02_Transects.csv: Details of 12 transects, survey efforts in each
 season and habitat for two hornbill species
 03_Hornbill_observations.csv: Contains details of 778 hornbill
 encounters during the transect surveys, including habitats and
 seasons 04_Hornbill_Distance.csv: Hornbill detections
 dataset from transect surveys used as input for density estimation
 analyses using Distance package in R
 05_Ficus_phenology.csv: Tree-wise observation dataset on fruiting
 phenology of figs from May 2017 to April 2018
 06_HornbillGLM.csv: A consolidated input file including
 covariates data used in the GLM analyses for both species of
 hornbills Sites.csv: This file provides details
 including locations of the transects surveyed. This file includes the
 following columns: <code>Sample.Label: Name of
 transect</code> <code>Transect_code: Unique
 code used for transect</code> <code>Length:
 Length of transect in km</code>
 <code>Effort: Total survey effort in
 km</code> <code>Start_lon: Start point
 (latitude) of transect in decimal degrees N</code>
 <code>Start_lat: Start point (longitude) of transect in
 decimal degrees E</code> <code>Start_elev:
 elevation at starting point in m, where available</code>
 <code>End_lon: End point (latitude) of transect in decimal
 degrees N</code> <code>End_lat: End point
 (longitude) of transect in decimal degrees E</code>
 <code>End_elev: elevation at ending point in m, where
 available</code> <code>Habitat: Whether
 Protected Area (PA) or plantation (Plantation)</code>
 <code>Remarks: Description of
 transect</code>