DOI: 10.5061/dryad.0cfxpnwcj
title: Data from: Interannual variation in foraging decisions in chick-rearing black-legged kittiwakes

description: Long-lived species must balance allocation between reproduction and
 self-maintenance, and such a trade-off is expected to affect their
 foraging behaviour. A bimodal foraging strategy, where individuals
 alternate between long trips for self-maintenance and short trips for
 offspring provisioning, may reflect this compromise. Using tracking data
 collected over three breeding seasons, we investigated the occurrence of a
 bimodal foraging strategy and inter-annual variation in foraging decisions
 among black-legged kittiwakes (Rissa tridactyla) breeding in Kongsfjorden,
 Svalbard. Kongsfjorden, a glacial fjord with six tidewater glacier fronts,
 provides close foraging opportunities to breeding sites. The continental
 shelf break outside the fjord offers another foraging area but involves
 higher commuting costs. We tested the hypothesis that breeding adults
 perform foraging trips outside the fjord for self-maintenance. We
 predicted that 1) adults were more likely to undertake foraging trips
 outside the fjord when their body condition was low and that 2)
 individuals foraging outside the fjord were likelier to improve their body
 condition than those foraging within. Our results indicate that kittiwakes
 in Kongsfjorden may adopt a bimodal foraging strategy during
 chick-rearing, but not every year. Contrary to our first prediction, we
 found no evidence that adult body condition affected the probability of
 foraging at distant sites. However, adults were more likely to maintain or
 improve body condition during outside-fjord foraging trips, supporting the
 hypothesis that long-distance trips can be used for self-maintenance.
 Overall, our results suggest that bimodal foraging is not a fixed
 characteristic of kittiwake foraging behaviour and may be influenced by
 environmental conditions.
description: # Interannual variation in foraging decisions in chick-rearing
 black-legged kittiwakes
 [https://doi.org/10.5061/dryad.0cfxpnwcj](https://doi.org/10.5061/dryad.0cfxpnwcj) **Overview** This dataset contains summarised GPS tracking data of black-legged kittiwakes (Rissa tridactyla), collected in Kongsfjorden, Svalbard, between 2016 and 2018. It provides detailed information on individual trips, distances travelled, and various biometric measurements. The dataset has been used in "Interannual variation in foraging decisions in chick-rearing black-legged kittiwakes" by Bertrand et al. 2025, published in Behavioral Ecology. ### Files and variables | **Column Name** | **Description** | | :-------------- | :-------------------------------------------------------------------------------------------------------------------------------------------- | | datetime | Timestamp of the first tracking point (UTC). Format: POSIXct/POSIXt. | | trackID | Unique identifier for each tracking session between capture and recapture. | | birdTrip | Unique identifier for each trip within a tracking session. Multiple trips can be associated with a single trackID. | | maxDist | Maximum distance flown per trip (in kilometers). | | ring | Individual ring number assigned to each bird. | | colony | Name of the colony where the bird was captured. | | stage | Breeding stage of the bird: "Incubation" or "Chick Rearing". | | sex | Sex of the bird (Male/Female). NA indicates unknown sex. | | Nest | Unique identifier for the bird's nest. | | Year | Year of data collection. | | WS | Weight of the bird at capture (in grams). | | WE | Weight of the bird at recapture (in grams). | | start | Timestamp of the bird's release at capture (UTC). Format: YYYY-mm-dd hh:mm. | | end | Timestamp of the bird's release at recapture (UTC). Format: YYYY-mm-dd hh:mm. | | HB | Head-bill measurement (in millimeters). | | MDbin | Binary variable indicating if the bird flew out of the fjord (1 = Yes, 0 = No). The threshold is determined relative to the colony of origin. | **Usage Notes** * The dataset is recorded in UTC time to ensure consistency across different locations. * The "trackID" represents the full tracking duration, whereas "birdTrip" identifies individual trips within a tracking session. * The "MDbin" column is based on a threshold specific to each colony, providing insight into whether birds venture beyond a defined area. * The "stage" variable can help differentiate movement behaviors between incubation and chick-rearing periods. **Citation & Acknowledgments** --- If using this dataset for research or publication, please cite the original data source and associated manuscript. For further inquiries or collaboration opportunities, please contact Philip Bertrand (mailto:[philip.bertrand1@gmail.com](mailto:philip.bertrand1@gmail.com)).