# Data from: Differences in foraging range between white-tailed tropicbirds breeding on inner and outer Seychelles Islands This dataset is published in the following paper: Ensanyar-Volle O, Appoo J, Bunbury N, Clucas G, Khan N, Rocamora G, Sanchez C, Fayet AL (2023) Differences in foraging range between white-tailed tropicbirds breeding on inner and outer Seychelles Islands. *Marine Ecology Progress Series* 724, 141–154, [https://doi.org/10.3354/meps14454]() There are two datasets: one with the birds' **GPS data** and associated metadata (*GPS_data.csv*), and one with the birds’ **GPS foraging locations and environmental variables** used in the Generalised Additives Models (GAMs) (*GAM_data.csv*). ## Description of the data and file structure All variables in each file are listed below. Details about the methods employed to obtain/calculate the variables are in the above paper. **GPS_data.csv** Each row corresponds to a GPS location – note these data are interpolated (see paper for details). · Lon: interpolated longitude, in decimal degrees · Lat: interpolated latitude, in decimal degrees · Bird: unique ring number to identify the bird · Local datetime: date and time in local time (GMT+4) · Sex: sex of the bird obtained from DNA (M=male, F=female, NA=unknown) · Colony: birds’ breeding colony, Aldabra Atoll or Aride Island · Stage: breeding stage (INC=incubation, CR= chick-rearing, INCCR=the egg was still intact when the trip started, but the chick had hatched by the time the trip ended) · Behaviour_HMM: behaviour (rest, foraging or relocation) as classified by Hidden Markov Models · Date: date · Trip_nb: trip number (each trip of each bird gets a unique number) **GAM_data.csv** Each row corresponds either to a foraging location recorded by GPS, or to a pseudo-random location used to generate a null distribution for the GAMs (see the paper for details). · Lon: longitude, in decimal degrees (note, for the “real” points this is interpolated) · Lat: latitude, in decimal degrees (note, for the “real” points this is interpolated) · Bird: unique ring number to identify the bird · Colony: birds’ breeding colony, Aldabra Atoll or Aride Island · Sex: sex of the bird obtained from DNA (M=male, F=female) · Trip_nb: trip number (each trip of each bird gets a unique number) · Datetime: date and time in local time (GMT+4) · Stage: breeding stage (INC=incubation, CR= chick-rearing) · Distance_from_nest_km: distance from the nest, in km · Date: date · chlA_monthly_mean: average chlorophyll A level at this location over the past month, in mg.m-3 · SST_monthly_mean: average SST at the location in the past month, in degrees Celsius · Bathymetry: water depth at the location, in m · Dist_seamount: distance to nearest seamount, in km · wind_speed: wind speed at the location and time, in m.s-1 · sum_fishing_effort: total fishing effort at that location during the study period, in hours. NA values mean no data were available for this location during the study period. · slope_degrees: slope of the sea floor at the location, in degrees Location_type: whether the location is a real foraging location recorded by a GPS logger (“real”) or a pseudo-randomly generated location (“pseudo”) ## Sharing/Access information The GPS data are also available on the BirdLife Seabird Tracking Database.

The foraging ecology and distribution of Phaethontiformes, an order of tropical seabirds, remains generally poorly understood, despite being essential to inform their conservation. Here, we tracked, for the first time, the foraging movements of breeding white-tailed tropicbirds Phaethon lepturus, a common but poorly studied seabird, in the Indian Ocean. We compared the foraging movements and habitat preferences of 2 populations, one from Aride Island in the inner Seychelles and the other from Aldabra Atoll in the outer Seychelles, ca. 1200 km to the southwest. We found considerable differences in foraging trip metrics between populations, with birds from Aride having an average foraging range 2 times greater (231 km on Aride vs. 105 km on Aldabra), and both populations feeding far beyond the protected areas around their respective colony. We also found differences in foraging range between incubation and chick-rearing stages and sexes. Using habitat models, we highlight the birds’ preference for deep waters, which may explain the greater foraging range of Aride birds, although human activities may also play a role. Our study provides unprecedented insight into the foraging ecology of white-tailed tropicbirds in the Western Indian Ocean.

The data collection methods are described in the paper and its electronic supplementary materials.