DOI: 10.5061/dryad.2z34tmq07
title: Loggers affect the foraging behaviour and fitness of European shags

description: Biologgers enable real-time collection of detailed behavioural and
 physiological data from wide-ranging animals, including seabirds
 inhabiting remote regions. However, the number of studies using tracking
 devices has not been matched by research exploring the behavioural and
 fitness costs of deployment, and the effects on data reliability. We
 assessed how GPS loggers, video loggers, and time depth recorders (TDRs)
 affect the behaviour, physiology, and reproductive performance of European
 shags (Gulosus aristotelis) breeding on Sklinna, Norway. The loggers
 varied in mass, attachment location, and deployment duration, allowing
 comparison of their relative effects. Birds without loggers served as
 controls to assess logger-related changes in adult body mass, chick
 growth, reproductive success, and survival. Birds with long-term
 tail-mounted GPS loggers and leg-mounted TDRs showed altered foraging
 behaviour, including shorter trips and dives, compared to birds with
 tail-mounted GPS and TDRs of the same weight, instrumented for only two
 days. A mean loss in body mass was experienced by adult birds regardless
 of the logger-type used, while chick growth rate dropped to 20% of that
 observed in control nests when video, TDR and GPS loggers (~4% of body
 mass) were deployed together. Logger attachments did not impact
 reproductive success and overall logger birds showed higher survival than
 controls. However female survival was lower than males among birds fitted
 with video and long-term GPS loggers. Our results demonstrate the
 importance of measuring behavioural and physiological effects that can
 scale over time. The advances in our understanding of animal ecology and
 behaviour generated by biologging have been impressive, but there is a
 need to consider the impacts on animal welfare and data quality.
 Consistent reporting of logger deployment details is essential to assess
 biologging impacts across species and refine protocols that account for
 device weight, drag and attachment location.
description: # Loggers affect the foraging behaviour and fitness of European shags
 Dataset DOI:
 [10.5061/dryad.2z34tmq07](https://doi.org/10.5061/dryad.2z34tmq07) ##
 Description of the data and file structure Below are the definitions of
 each variable included in the six datasets used for the analysis in our
 paper *“Loggers affect the foraging behaviour and fitness of European
 shags.”* These descriptions are provided to aid correct interpretation and
 reuse of the data. **1. Foraging behaviour (dataset: Foraging_trip.csv)**
 | **Variable** | **Definition** | | :----------- |
 :--------------------------------------------- | | trip\_id | Unique ID
 for each recorded foraging trip | | sex | Male or Female | | year | Year |
 | TripComp | Trip completed | | N | Number of GPS locations | | maxdist |
 Maximum distance from the colony in metres | | start | Start date and time
 (format: DD.MM.YYYY HH:MM) | | end | End date and time (format: DD.MM.YYYY
 HH:MM) | | length | Length of trip in decimal hours | | tag | Type of
 logger used (IgotU, pathT or video) | | duration | Time since the logger
 was deployed in days | **2. Dive behaviour (dataset: Dive_behaviour.csv)**
 | **Variable** | **Definition** | | :---------------- |
 :----------------------------------------------------------- | | botttim |
 Bottom time in seconds | | divetim | Total dive time in seconds | | maxdep
 | Maximum depth in metres | | observation | Observation number | | year |
 Year | | tag | Type of logger used (IgotU, pathT or video) | | duration |
 Time since the logger was deployed in days | | sex | M or F | |
 begdesc\_original | Date and time that a dive started (format: DD.MM.YYYY
 HH:MM) |   **3. Adult body mass (dataset: Adult_weight_diff.csv)** |
 **Variable** | **Definition** | | :----------- |
 :---------------------------------------------------------------------------- | | sex | Male or Female | | weight\_diff | Change in weight (g) over duration of season (control) or deployment (logger) | | tagged | Tagged or untagged birds | | logger | Control (no logger), IgotU, video or pathT | **4. Chick growth rate (dataset: Chick_growth_rate.csv)** | **Variable** | **Definition** | | :------------ | :----------------------------------------- | | UniqueChickID | Unique ID number for each chick | | growth\_rate | Growth rate (g/day) | | logger | Control (no logger), IgotU, video or pathT | **5. Chick survival (dataset: Chick_survival.csv)** | **Variable** | **Definition** | | :-------------- | :----------------------------------------------------------------------------- | | nest\_no | Nest number | | year | Year | | start\_clutch | Number of eggs or chicks in the clutch at first observation | | end\_clutch | Number of eggs or chicks in the clutch at the final observation | | prop\_surv | Proportion of chicks that survived | | adj\_prop\_surv | Adjusted proportion accounting for small sample size (see methodsin the paper) | | data | Control (no logger) or PathTrack |   **6. Adult survival (dataset: Adult_survival.rds)** An rds file containing capture history, logger assignments, and sex. The file `Adult_survival.rds` can be loaded into R using `data &lt;- readRDS("Adult_survival.rds")`. This creates a list containing the capture history matrix (`CH`), logger assignment matrix (`Logger_mat`), and sex vector (`Sex`). Users can access these components (e.g., `data$CH`) to explore the data or use the capture histories directly in mark–recapture or survival analyses with packages such as** RMark **or** marked.** | **Object** | **Variable** | **Definition** | | :------------------- | :----------- | :----------------------------------------------------------------------- | | Capture history (CH) | – | Record of capture occasions for each individual (mark–recapture format). | | Logger matrix | – | Matrix showing which individuals carried which logger type in each year. | | Logger codes | 2 | IgotU, Pathtrack\_short | | | 3 | Video, Video\_dummy | | | 4 | Pathtrack\_4weeks, Pathtrack, Ornitela | | Sex | 0 | Female | | | 1 | Male |