Effects of geolocators on hatching success, return rates, breeding movements, and change in body mass in 16 species of Arctic-breeding shorebirds

Background Geolocators are useful for tracking movements of long-distance migrants, but potential negative effects on birds have not been well studied. We tested for effects of geolocators (0.8–2.0 g total, representing 0.1–3.9 % of mean body mass) on 16 species of migratory shorebirds, including five species with 2–4 subspecies each for a total of 23 study taxa. Study species spanned a range of body sizes (26–1091 g) and eight genera, and were tagged at 23 breeding and eight nonbreeding sites. We compared breeding performance and return rates of birds with geolocators to control groups while controlling for potential confounding variables. Results We detected negative effects of tags for three small-bodied species. Geolocators reduced annual return rates for two of 23 taxa: by 63 % for semipalmated sandpipers and by 43 % for the arcticola subspecies of dunlin. High resighting effort for geolocator birds could have masked additional negative effects. Geolocators were more likely to negatively affect return rates if the total mass of geolocators and color markers was 2.5–5.8 % of body mass than if tags were 0.3–2.3 % of body mass. Carrying a geolocator reduced nest success by 42 % for semipalmated sandpipers and tripled the probability of partial clutch failure in semipalmated and western sandpipers. Geolocators mounted perpendicular to the leg on a flag had stronger negative effects on nest success than geolocators mounted parallel to the leg on a band. However, parallel-band geolocators were more likely to reduce return rates and cause injuries to the leg. No effects of geolocators were found on breeding movements or changes in body mass. Among-site variation in geolocator effect size was high, suggesting that local factors were important. Conclusions Negative effects of geolocators occurred only for three of the smallest species in our dataset, but were substantial when present. Future studies could mitigate impacts of tags by reducing protruding parts and minimizing use of additional markers. Investigators could maximize recovery of tags by strategically deploying geolocators on males, previously marked individuals, and successful breeders, though targeting subsets of a population could bias the resulting migratory movement data in some species. Electronic supplementary material The online version of this article (doi:10.1186/s40462-016-0077-6) contains supplementary material, which is available to authorized users.

download. The exact date and time of activation for each device was also recorded as a baseline time stamp for the data collected.
All birds caught received a metal bird band issued by the Australian Bird and Bat Banding Society which was placed on the left tarsus along with a green engraved leg flag placed on the right tibia. Those birds selected for geolocator attachment also received a yellow leg flag with the geolocator attached which was placed on the left tibia. Returning birds were caught using cannon nets and the flag with geolocator removed in the field. The metal band and green engraved flag was left on the bird to allow further observations of the individual.

GeoSpoi
Site: B19 Species: WHIMisl Detailed field methods have been published for the control birds [10,11]. Geolocators were Intigeo-W65, Migrate Technology Ltd and were attached with a cable tie and leg flag for a total mass of ~ 1 g.

Gilg, Lang, & Bollache
Sites: B17, B20 Species: SANDalb Field methods followed those described in the main text. Details about field site B17 are available in the literature [12,13].

Lanctot & Yezerinac
Sites: B02, B05 Species: DUNLpac Field methods followed those of the Arctic Shorebird Demographics Network [6], except no defined study plots were used and nests were not monitored.

Reneerkens et al.
Site: B18 Species: SANDalb The field site is approximately 60 km 2 large and was annually visited for 4-8 weeks in June and July by 1-2 teams of 1-3 persons. Researchers, on foot, were solely focusing on sanderlings and used spotting telescopes to read color-banded sanderlings [18,19]. Adult and juvenile sanderlings were annually color-banded in the whole area. Each year the whole area was searched for nests and color-banded individuals, but especially early in the season snow cover limited the time that can be spend in areas further away from the field station. It is for this reason that we tried as much as possible to deploy geolocators to birds nesting in two sub-areas within the total study area, that were close to the field station and/or bred in areas that are usually snow-free early in the season. Birds were mostly captured on the nest using a small clapnet, but adults guiding chicks were also captured with mistnets. Small spacer bands were applied below the flag with the geolocator to enable free movement of the flag and distribute the weight equally on the leg joint.

Taylor et al.
Site: B01 Species: BLTU We trimmed feathers from a geolocator-sized area about 2 cm above the uropygial gland and glued the geolocator to this site using Loctite 454 cyanoacrylate instant adhesive. We used 1.0 mm thick Stretch Magic beading cord to secure the geolocator in place with the leg-loop harness described by Warnock & Warnock [10]. The light sensor of the geolocator (Lotek MK 5780, 1.5 g) was on a 20mm stalk attached at 30 degree angle. We searched for all birds that were banded in 2013 when we returned in 2014; this entailed spending ~200 hours searching the plots. We spent about 4 hours off-plot looking specifically for geolocator birds.

Ward & Helmericks
Site: B09 Species: RUTUmor Observations and captures of ruddy turnstones were made at the Helmericks homestead located on the north end of Anachlik Island at the mouth of the Colville River Delta, Alaska, 2011-2014. All captures were made with a bow trap by baiting birds to a trap site with food and marking followed procedures in Brown et al. [6]. Observations of marked birds were made primarily at the trap site and occasionally at other locations on the island.  Table S1. Study sites included in the analysis of geolocator effects on shorebirds. Breeding areas are indicated with "B" code while nonbreeding areas are indicated with an "N"; sites in each category are numbered from west to east.   Figure 2). Table S3. Model-averaged effects of geolocators on nest success for six species of Arctic-breeding shorebirds. Species are sorted by ascending body mass; codes are defined in Table 1. All models included random effects of site and year. Submodel sets are given in Table S4; sample sizes are given in Table 2 Table S8. Model-averaged effects of geolocator orientation on nest success and return rate for semipalmated sandpipers at site B03 and return rate for American golden-plovers at site B16. Effect size estimates are given as mean (SE), and effects of two geolocator leg attachments were tested: PAB = parallel-band; PEF = perpendicular-flag. Top model sets are provided in Table S9; sample sizes are in Table S2. See Table S4 Figure S1. Nest success and partial hatching of clutches of control and geolocator nests for Arcticbreeding shorebirds. a) Proportion of nests hatched of those with known fate for control and geolocator groups of six species of Arctic-breeding shorebirds at a subset of sites. b) Proportion of hatched nests with unhatched eggs remaining for control and geolocator birds for five species. A dash instead of a bar indicates no data available for a given group to distinguish from groups for which no successful nests or no unhatched eggs were recorded. Species are ordered from smallest to largest; species codes are defined in Table 1 and site codes are in Table S1; sample sizes are given in Table S2. Figure S3. Proportion of shorebirds with and without geolocators that returned to each site one year after capture. A dash instead of a bar indicates no data for a given group to distinguish from cases where birds were marked but none returned. Species are ordered from smallest to largest; species codes are defined in Table 1, site codes are given in Table S1, and sample sizes are given in Table S2.