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

Abstract

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 18.4% decrease of the abundance of wintering and seed-disperser species, respectively. Seasonal abundance peaks were advanced for at least one month in the 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.

Lasting effects of avian‐frugivore interactions on seed dispersal and seedling establishment

“…For example, most of the (few) seeds arriving at open areas are brought by a single bird species, Turdus merula . Hence, this disperser must play an important role in colonising new spaces, and its eventual local disappearance could have important consequences on P. lentiscus' colonisation ability and plant community structuring (Campo‐Celada et al., 2022; González‐Varo et al., 2017; Isla et al., 2023). The overall spatial clumping of the seed rain was concordant with many previous studies (e.g.…”

“…The loss of certain avian species with specific phenologies (e.g. frugivorous wintering migrants; see Campo‐Celada et al., 2022) and preferences for fruit consumption and land‐use may impact plant recruitment in the most suitable microhabitats, having lasting consequences in plant regeneration and vegetation physiognomy.…”

Lasting effects of avian-frugivore interactions on seed dispersal and seedling establishment

“…For example, most of the (few) seeds arriving at open areas are brought by a single bird species, Turdus merula. Hence, this disperser must play an important role in colonising new spaces, and its eventual local disappearance could have important consequences on P. lentiscus' colonisation ability and plant community structuring (Campo-Celada et al, 2022;González-Varo et al, 2017;Isla et al, 2023). The two major dispersers of P.…”

Biotic Indicators for Ecological State Change in Amazonian Floodplains

“…Community-wide alterations in body condition, with increasing or decreasing trends, driven by changes in food availability and quality have been reported in a broad array of consumers (e.g., Neotropical freshwater fish, Pereira and Agostinho 2019 ; frugivorous birds, Campo-Celada et al. 2022 ; marine fish, birds, and mammals, Harwood et al. 2015 ).…”