Survival probability in a small shorebird decreases with the time an individual carries a tracking device

Abstract

Effects of tracking devices on survival are generally considered to be small. However, most studies to date have been conducted over a time-period of only one year, neglecting the possible accumulation of negative effects and consequently stronger negative impacts on survival when the individuals have carried the tracking devices for longer periods. We studied the effects of geolocators in a closely monitored and colour-ringed southern dunlin Calidris alpina schinzii population breeding in Finland. Our capturerecapture data spans 2002-2018 and includes individual histories of 338 colour-ringed breeding adult dunlins (the term 'recapture' includes resightings of colour-ringed and individually recognizable birds). These data include 53 adults that were fitted with leg-flag mounted geolocators in 2013-2014. We followed their fates together with other colour-ringed birds not equipped with geolocators until 2018. Geolocators were removed within 1-2 years of attachment or were not removed at all, which allowed us to examine whether carrying a geolocator reduces survival and whether the reduction in survival becomes stronger when geolocators are carried for more than one year. We fit multi-state open population capture-recapture models to the encounter history data. When assessing geolocator effects, we accounted for recapture probabilities, time since marking, and sex and year effects on survival. We found that carrying a geolocator reduced survival, which contrasts with many studies that examined return rates after one year. Importantly, survival declined with the time the individual had carried a geolocator, suggesting that the negative effects accumulate over time. Hence, the longer monitoring of birds carrying a geolocator may explain the difference from previous studies. Despite their larger mass, females tended to be more strongly affected by geolocators than males. Our results warrant caution in conducting tracking studies and suggest that short-term studies examining return rates may not reveal all possible effects of tracking devices on survival.

Animal lifestyle affects acceptable mass limits for attached tags

“…One direct aspect that exemplifies this is, for example, measurable physical harm to the animal, such as pressure sores [12], the severity of which might be expected to depend on movement patterns. However, physical harm can also effectively occur if tagged animals or their offspring cannot balance energy budgets owing to compromised foraging stemming from tag interference [6,30,31]. Often, this is simply a result of higher movement costs or reduced performance in tagged animals as they travel [18].…”

Natal dispersal does not entail survival costs but is linked to breeding dispersal in a migratory shorebird, the southern dunlinCalidris alpina schinzii

“…Analyses were performed in program MARK (White and Burnham 1999). In order to control for the effect of geolocators on survival (Pakanen et al 2020), we added to each model an individual covariate (binary variable) distinguishing individuals that carried a geolocator from year i to year i + 1 (1) from those that did not (0). Starting from the full model, we explored all possible sub‐models down to the constant model (i.e.…”

“…In the Finnish population, adult birds were fitted with geolocators during 2013-2014 for the purpose of studying migration ecology and wintering site use (Pakanen et al 2018). These tracking devices did not affect reproduction but affected survival especially when the individuals carried them for more than one year (Pakanen et al 2015a(Pakanen et al , 2020.…”

“…This model fitted the data (Bootstrapping goodness of fit, p = 0.10, ĉ = 1.08; White et al 2002). Our model did not account for temporal variation in survival because a previous analysis based on a larger data set did not find support for differences between years (Pakanen et al 2020). Analyses were performed in program MARK (White and Burnham 1999).…”

Casting the Net Widely for Change in Animal Welfare: The Plight of Birds in Zoos, Ex Situ Conservation, and Conservation Fieldwork

“…One study used several species of migratory geese and found that those with attached harnesses had lower return rates [ 222 ]. Another 18-year-long study of the southern dunlin Calidris alpina schinzii , a small migratory wader in Finland, confirmed that the attachment of geolocators resulted in reduced survival [ 223 ]. Importantly, death rates increased more markedly the longer the birds carried the device [ 223 ].…”