Assessing short and long-term variations in diversity, timing, and body condition of frugivorous birds

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.Medata information: File: censuses80s_20s.txt 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: ringing80s_20s.txt 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. Funding provided by: Horizon 2020 Framework ProgrammeCrossref Funder Registry ID: http://dx.doi.org/10.13039/100010661Award Number: 798269Funding provided by: Consejería de Economía, Conocimiento, Empresas y Universidad, Junta de AndalucíaCrossref Funder Registry ID: http://dx.doi.org/10.13039/100016970Award Number: P18-HO-4814Funding provided by: Agencia Estatal de InvestigaciónCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100011033Award Number: CGL 2017-82847Data 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