DOI: 10.5061/dryad.p2ngf1vrt
title: Assessing short and long-term variations in diversity, timing, and body condition of frugivorous birds

description: Seed dispersal by frugivorous bird species involves a fine temporal tuning
 between fruiting plants and birds. However, this interaction may be
 severely threatened by anthropogenic climate and land-use change, which
 may result in phenological mismatches and pervasive ecological
 consequences for avian communities. In this study, we evaluate changes at
 long (~40 years) and short-time (seasonal) spans in an avian frugivore
 community using a snapshot resampling. Particularly, we focus on changes
 in composition, abundance, migratory timing (i.e., phenology), and
 physical condition in relation to variations in fruit supply. We used bird
 and fruit data collected during 1981-1983 and 2019-2021 in a Mediterranean
 scrubland site in Doñana Natural Area, SW Spain. Our findings indicate a
 profound transformation of species composition, bird phenology, and body
 condition: in ~40 years, the avian community showed a 66% and 13% decrease
 of the wintering and seed-disperser species, respectively. Seasonal
 abundance peaks were advanced for at least one month in 9 out of 11
 frugivorous bird species included in the analyses. Avian body condition
 during the migratory passage has worsened, with fewer individuals showing
 a high-fat percentage now than in the past. Finally, we report a fruit
 production decrease of almost half in 2019-2021 compared to 1981-1983,
 probably linked to habitat encroachment by pine trees and replacement of
 fleshy-fruited shrubs. Vegetation encroachment and climate change are the
 most plausible explanations for the observed changes in the avian
 community, but the relative importance of these factors is yet unknown.
 Our results at a local scale mirror the dramatic consequences of global
 change affecting the diversity, phenology, and physical condition of
 frugivorous bird species reported in multiple studies across the globe.
 The loss of frugivores may trigger feedback mechanisms in which seed
 dispersal is disrupted, leading to impaired recruitment of fruiting plants
 and hence less food availability for the avian community.
description: Data include two different datasets (each one separated in a
 different file): 1) Bird abundance data; 2) Bird trapping data using mist
 nets. Data were collected in Hato Ratón, in Doñana’s Natural Area, close
 to Villamanrique de la Condesa, Sevilla province, southern Spain (37° 10’
 26.4” N, 6° 20’ 17.4” W, 11 m a.s.l.). Sampling was carried on in two time
 periods: 1981-1983 and 2019-2021. Bird abundance was
 estimated using 1-km linear transects to calculate the kilometric
 abundance index. These were conducted 2-5 times per month (40 censuses in
 total). For each individual that was seen or heard, we recorded its
 species and the time it was seen. Bird censusing started one hour after
 sunrise and was carried out when weather conditions were not extreme (in
 absence of rain or strong wind). Data on censed birds include a total of 0
 species. Bird ringing data comes from birds captured by
 mist nets deployed weekly during 1981-1983 (6-10 nets per survey day,
 average 10-25 mist-net m/h) and fortnightly in 2019-2021 (12-20 nets per
 survey day, average 25-50 m/h). Data on trapped birds include a total of
 32 species.
description: Medata information:
 File: <strong>censuses80s_20s.txt</strong>
 Including abundance censuses carried on in 1981-1983 and
 2019-2021- Variable names: yeargroup (study period,
 either 1981-1983 or 2019-2021), Date (Year/Month/Day), year, months,
 Transect, species, count (number of individuals), distance (transect
 length), ikas (relative abundance, individuals/km).
 File: <strong>ringing80s_20s.txt</strong>
 Including bird ringing data carried on in 1981-1983 and
 2019-2021- Variable names: Date (Year/Month/Day),
 Species, Tarsus length (mm), Weight (g), residuals (Weight ~ tarsus
 residuals), Fat_rescaled (fat value after rescaling, from 0 to 8), fat_cat
 (Fat category: low or medium-high fat content), Migratory_type (Resident,
 Summer, Wintering, or Migrant), Trophic_type (combinations of Herbivore,
 Frugivore, Insectivore, Granivore, Carnivore, Omnivore, and
 Necrophage), Functional type (NF, PC, SP, SD, PC/SP/SD, PC/SP). NF = Non
 Frugivore; PC = Pulp Consumer; SP = Seed Predator; SD = Seed
 Disperser.