Granadeiro, J. P. | bioRxiv Science

bioRxiv2026

Associations of waterbirds with harvesting and ploughing events in rice fields: increasing foraging opportunities or just gathering for the feast?

Surges in food availability create localized but intense foraging opportunities, often attracting multi-species consumer groups. Agricultural practices can trigger these surges, prompting bird associations. However, the strength and duration of the association, as well as its drivers, remain unclear. This study examines waterbird association with harvesting and ploughing events in rice fields. The duration and magnitude of these associations were determined and three hypotheses addressed to explain them: (1) increased food availability, (2) enhanced foraging success and (3) reduced time allocated to vigilance. Waterbird counts and GPS tracking revealed strong associations with management events. Bird numbers spiked during events but declined within one to two days. Food availability (and soil penetrability) increased significantly during events - crayfish and rice during harvesting, worms and soil penetrability during ploughing - supporting Hypothesis 1. However, this did not improve foraging performance (intake rate, foraging success), rejecting Hypothesis 2. Higher competition, interference or kleptoparasitism in these large mixed-species flocks may offset increased food availability benefits. Alternatively, functional responses of target species may limit prey intake due to physiological or behavioural constraints. Hypothesis 3 was also unsupported, as birds did not reduce vigilance. It is plausible that birds may be drawn to events by the perception of a feast, not actual benefits. Gregariousness and foraging behaviour by "local enhancement" may explain such associations. Results highlight the complexity of bird responses to food surges while suggesting waterbirds in rice fields maintain stable foraging performance during agricultural management events and otherwise, indicating resilience to agricultural timing shifts.

ecology↗

bioRxiv2023

Connectivity of marine predators over the Patagonian Shelf during the highly pathogenic avian influenza (HPAI) outbreak

Animal movement and population connectivity are key areas of uncertainty in efforts to understand and predict the spread of infectious disease. The emergence of highly pathogenic avian influenza (HPAI) in South America poses a significant threat to globally significant populations of colonial breeding marine predators in the South Atlantic. Yet, there is a poor understanding of which species or migratory pathways may facilitate disease spread. Compiling one of the largest available animal tracking datasets in the South Atlantic, we examine connectivity and inter-population mixing for colonial breeding marine predators tagged at the Falkland Islands. We reveal extensive connectivity for three regionally dominant and gregarious species over the Patagonian Shelf. Black browed albatrosses (BBA), South American fur seals (SAFS) and Magellanic penguins (MAG) used coastal waters along the Atlantic coast of South America (Argentina and Uruguay). These behaviours were recorded at or in close proximity to breeding colonies and haul-out areas with dense aggregations of marine predators. Transit times to and from the Falkland Islands to the continental coast ranged from 0.2 - 70 days, with 84% of animals making this transit within 4 days - a conservative estimate for HPAI infectious period. Our findings show the incursion of HPAI to the Falkland Islands marine predator community is a highly credible threat, which may be facilitated by BBA, SAFS and MAG connectivity with South America. This information is vital in supporting HPAI disease surveillance, risk assessment and marine management efforts across the region. SignificanceThe recent emergence of highly pathogenic avian influenza (HPAI) in South America poses a major threat to globally significant marine predator populations in the South Atlantic. There is extensive connectivity over the southern Patagonian Shelf between regionally dominant seal and seabird populations, with potential for large-scale pathogen spread. Despite this connectivity, outbreaks of HPAI are unevenly distributed across the region. Connectivity information is integral for regional disease surveillance, predictive modelling and population viability assessments.

ecology↗