Year-round at-sea distribution and trophic resources partitioning between two sympatric Sulids in the tropical Atlantic

PLoS One. 2021 Jun 21;16(6):e0253095. doi: 10.1371/journal.pone.0253095. eCollection 2021.

Abstract

In the oligotrophic tropical marine environment resources are usually more patchily distributed and less abundant to top predators. Thus, spatial and trophic competition can emerge, especially between related seabird species belonging to the same ecological guild. Here we studied the foraging ecology of two sympatric species-brown booby (BRBO) Sula leucogaster (breeding) and red-footed boobies (RFBO) Sula sula (non-breeding)-at Raso islet (Cabo Verde), across different seasons. Sexual segregation was only observed during Jun-Oct, when RFBO were present, with larger females BRBO remaining closer to the colonies, while males and RFBO travelled further and exploited different habitats. Overall, species appeared to prefer areas with specific oceanic features, particularly those related with oceanic currents and responsible for enhancing primary productivity in tropical oceanic areas (e.g. Sea Surface Height and Ocean Mixed Layer Thickness). Female BRBOs showed high foraging-site fidelity during the period of sympatry, while exploiting the same prey species as the other birds. However, during the months of co-existence (Jun.-Oct.), isotopic mixing models suggested that female BRBO would consume a higher proportion of epipelagic fish, whereas female RFBO would consume more squid compared to the other birds, possibly due to habitat-specific prey availability and breeding energy-constraints for BRBO. We conclude that divergent parental roles, environmental conditions, habitat preference and competition could be mechanisms simultaneously underlying sexual segregation for BRBO during a period of co-existence, while inter-specific foraging differences appear to be more affected by habitat preference and different breeding stages. These results support previous statements that BRBO can adapt their foraging ecology to different circumstances of environmental conditions and competition, and that marine physical features play an important role in foraging decisions of boobies.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animal Distribution / physiology*
  • Animals
  • Birds / physiology*
  • Ecosystem*
  • Feeding Behavior*
  • Female
  • Male
  • Nutritional Status
  • Oceans and Seas
  • Seasons*
  • Sympatry*

Grants and funding

This work received financial and logistic support (for fieldwork campaigns, GPS tracking devices and laboratory analysis) from the project Alcyon – Conservation of seabirds from Cabo Verde, coordinated by BirdLife International and funded by the MAVA foundation (MAVA17022; http://en.mava-foundation.org), through its strategic plan for West Africa (2017-2022). NA is also most thankful to MAVA foundation for the granted PhD fellowship which allowed to develop this work. This study also benefitted from funding by the strategic program of MARE, financed by FCT (UID/MAR/04292/2020), through national funds. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.