Effect of GPS tagging on behaviour and marine distribution of breeding Arctic Terns Sterna paradisaea

Abstract

Tracking tags have been used to map the distributions of a wide variety of avian species, but few studies have examined whether the use of these devices has impacts on the study animals that may bias the spatial data obtained. As Global Positioning System (GPS) tags small enough for deployment on terns (family: Laridae) have only recently become available, until now tracking of this group has been conducted by following unmanipulated individuals by boat, which offers a means of comparing distributions obtained from GPS‐tracking. We compared the utilization distributions (UDs) of breeding Arctic Terns Sterna paradisaea obtained by GPS‐tracking 10 individuals over 2 weeks, with UDs derived from contemporaneous visual boat tracks from 81 individuals. The 50% and 95% UDs of both methods had high similarity scores, indicating good agreement in the density distributions derived from the two methods. The footprints of the UDs of tagged birds were ~ 75–80% larger, which may reflect an effect of tagging on foraging range or the occasional inability to follow by boat individuals which roamed further from the colony. We also compared the nest attendance and chick provisioning rates of adults that were (1) fitted with a GPS tag and leg‐flag, (2) handled and marked with a leg‐flag but not tagged and (3) fitted with a leg‐flag in a previous year but unhandled in the year of the study. There was some evidence that birds fitted with both a GPS tag and leg‐flag spent slightly less time at the nest compared with unhandled birds and those fitted with a leg‐flag only. Both treatments where birds were fitted with a leg‐flag in the year of the study had similarly lower provisioning rates to those of unhandled control birds > 48 h after handling, suggesting that negative effects on provisioning are due to capture and handling or leg‐flag attachment rather than to GPS tag attachment/loading per se. Overall brood‐provisioning rate was compensated for by the increased effort by the unhandled partner. Our study suggests that despite slight effects of GPS‐tagging on behaviour, the estimates of marine density distribution obtained were very similar to those of unmanipulated birds.

Foraging Behaviours of Breeding Arctic Terns Sterna paradisaea and the Impact of Local Weather and Fisheries

“…The total area across which arctic terns foraged (average 95% isopleth area) was 16-218 times larger than reported by Robertson et al (2014b) who tracked terns visually. Visually tracking arctic terns in boats appears to lead to smaller utilisation distributions than studies using tracking devices (Seward et al, 2020). However, arctic terns carrying GPS tracking devices in the Skerries, Wales also had smaller mean estimated home ranges (half to one fortieth of those recorded in this study) (Seward et al, 2020).…”

“…It is likely that the distances and home ranges that we report here reflect the space use of arctic terns breeding elsewhere in Iceland as Seward et al (2020) reported that the home ranges of GPS tagged and non-GPS tagged arctic terns were comparable. Indeed, if there is an effect of carrying the device on the birds (Geen et al, 2019;Tomotani et al, 2019), we might expect other arctic terns to travel even further without the burden of a tracking tag.…”

“…Visually tracking arctic terns in boats appears to lead to smaller utilisation distributions than studies using tracking devices (Seward et al, 2020). However, arctic terns carrying GPS tracking devices in the Skerries, Wales also had smaller mean estimated home ranges (half to one fortieth of those recorded in this study) (Seward et al, 2020). The smaller home ranges reported in Wales compared to those we recorded in Iceland could be a result of tracking terns during chick rearing, restrictions by land masses, or interspecific competition with other tern species reducing foraging areas due to resource or niche partitioning (Robertson et al, 2014b).…”

What is our power to detect device effects in animal tracking studies?

“…Nevertheless, we recommend that researchers invest time in designing means of empirically examining the impact of tagging devices (e.g. Cleasby et al., 2020; Evans et al., 2020; Seward et al., 2020). Researchers will have to decide which impacts are most relevant to their study species and over what time period such effects will manifest themselves.…”

Migratory movements of British and Irish Common Shelduck Tadorna tadorna: a review of ringing data and a pilot tracking study to inform potential interactions with offshore wind farms in the North Sea

“…Tags were attached, under licence, by trimming body feathers from the mantle, just posterior to the chestnut mantle band, and supergluing the tag with a muslin base directly to the skin and the 1-2-mm remainder of the trimmed feather shafts. This attachment method was an adaptation of that used by Seward et al (2020). The combined additional weight of metal ring, colour ring, tag, muslin and glue was on average ∼26 ± 0.4 g, which equated to less than 3% of the body mass of each bird (1142.5 ± 197.1 g).…”