Biologging devices are providing detailed insights into the behaviour and movement of animals in their natural environments. It is usually assumed that this method of gathering data does not impact on the behaviour observed. However, potential negative effects on birds have rarely been investigated before field‐based studies are initiated. Seabirds which both fly and use pursuit diving may be particularly sensitive to increases in drag and load resulting from carrying biologging devices. We studied chick‐rearing adult common guillemots (Uria aalge) equipped with and without back‐mounted GPS tags over short deployments of a few days. Concurrently guillemots carried small leg‐mounted TDR devices (time‐depth recorders) providing activity data throughout. Changes in body mass and breeding success were followed for device equipped and control guillemots. At the colony level guillemots lost body mass throughout the chick‐rearing period. When‐equipped with the additional GPS tag, the guillemots lost mass at close to twice the rate they did when equipped with only the smaller leg‐mounted TDR device. The elevated mass loss suggests an impact on energy expenditure or foraging performance. When equipped with GPS tags diving performance, time‐activity budgets, and daily patterns of activity were unchanged, yet dive depth distributions differed. We review studies of tag‐effects in guillemots (Uria spp.) finding elevated mass loss and reduced chick‐provisioning to be the most commonly observed effects. Less information is available for behavioural measures, and results vary between studies. In general, small tags deployed over several days appear to have small or no measurable effect on the behavioural variables commonly observed in most guillemot tagging studies. However, there may still be impacts on fitness via physiological effects and/or reduced chick‐provisioning, while more detailed measures of behaviour (e.g. using accelerometery) may reveal effects on diving and flight performance.

Using a noose-pole, we caught 36 adult common guillemots rearing chicks on a natural rock ledge below the Karlsö Murre lab (8–25th June 2015) (Hentati-Sundberg  et  al. 2012, Evans  et  al. 2013). Individuals were randomly allocated to one of four groups (Fig. 1) following a controlled crossover design (Wellek and Blettner 2012): experimental guillemots (with devices) with two order groups (caught three times); full controls (caught twice); and background controls (caught once). Twelve guillemots were tagged with devices, all of which were followed for 4.3 ± 0.9 days (mean ± SD) with GPS and TDR and also for 3.5 ± 1.0 days with TDR only, with the order of deployments swapped for half the group. We additionally captured 24 control guillemots throughout the study period, five of which were full controls, caught twice, allowing their individual changes in mass to be followed, and 19 of which were captured once. The 19 background controls, together with the first capture information (i.e. prior to any potential treatment effect) for all guillemots (including the 12 experimental and five full controls), were used to infer whether there were any background colony level trends in mass.

Further methods includes in article (https://doi.org/10.1111/jav.02509).

File descriptions

capture_info_all.csv

Capture details for all guillemots, includes capture date, body mass, and experimental group.
Experimental group (TYPE), has control (guillemots caught once), contol2 (guillemots caught twice), device (those with devices).
Capture - capture occasion (1, 2, or 3).

capture_info_deviced.csv

Capture details for guillemots that had devices deployed. Has same information as capture_info_all.csv with addition of chick hatch date and age.
bouts_all.csv
Dive bout level information. Includes key dive bout paramaters. Includes calculated sea surface temperature pre-bout (see article for details).

dives_all.csv

File contains all recorded dives, with summary information for each dive.
Headings provide variable name and unit.
Includes key extracted metadata used in the analysis (sun elevation, day period).
Several variables allow connecting with other files (e.g. ring_number, TDR_deployment_id, dive_bout_id)

time_activity_budget.csv

Time activity budget information for guillemots, derived from TDR data. Includes proportion of each day spent diving (dive_time_p), on post dive intervals per day (pdi_time_p). Also total time for each activity in seconds per day and broken down by night and day time (e.g. dive_time_total_day).