Colour-ring wear and loss effects in citizen science mark-resighting studies

Background: Ring wear and loss may have important consequences for mark-recapture studies that aim to estimate survival trends. Our study quantifies the rates of wear and loss from a long-running colour-ringing project of the Eurasian Oystercatcher (Haematopus ostralegus) in the Netherlands. Methods: Our analysis included 8909 colour-ringed oystercatchers with 118,071 resightings, predominantly ringed and observed by citizen scientists. We quantified how ring wear and loss may vary with ring colour and age, and how this may impact resighting probabilities. We then determined how ring loss may impact survival estimates and resighting probabilities of mark-recapture models by simulating four scenarios of how citizen scientists may resight and report birds with lost colour rings. Results: Annual rates of colour ring loss averaged 2.5% compared with 1% for ring wear, but lost rings also had a higher reporting probability (31.2%) than worn rings (10.3%). Lost rings may not directly impact survival estimates since 50% of oystercatchers with lost rings could still be uniquely identified. Ring wear and loss rapidly increased between 10 and 15 years after ringing. Rates of ring loss were comparable amongst ring colours, but the wear rate appeared higher for red and white rings compared to other colours. Rates of ring wear and loss varied significantly amongst different regions in our study, which were characterised as having different habitat features. Differential rates of ring wear may have important implications for studies conducted over large geographical scales or of multiple species. Conclusions: Based on simulations of ring loss in our population, estimates of apparent survival may be 0.3–1.2% lower whilst the impact of ring wear was deemed even lower. We developed a table of recommendations containing advice for ring fitting, data collection, study design, and mark-recapture analyses, so that future colour-ringing studies can benefit from our experiences in collecting and analysing data of ring wear and loss through citizen science.

Disturbance increases high tide travel distance of a roosting shorebird but only marginally affects daily energy expenditure

Background:Anthropogenic disturbance can negatively affect an animal's energy budget by evoking movement responses.Existing research focuses mainly on immediate displacement as a disturbance effect,since this can be easily observed in the field. However, effects on movement over longer timescales are poorly examined and it is largely unknown if and to what extent they reflect immediate responses.Longer-term responses could for example be larger than immediate responses if birds, after disturbance, return to the original location and thereby travel twice the immediate disturbed distance. Methods:We combined GPS tracking data with observational data to quantify the effects of anthropogenic (air force and walkers) and non-anthropogenic disturbances on distances travelled by roosting Eurasian Oystercatchers (Haematopus ostralegus) during the non-breeding season. We compared immediate displacement after a disturbance with distance travelled during the entire high tide period (longer-term response), while accounting for environmental factors.Additionally,we calculated energy expenditure due to disturbance based on observed disturbance frequencies.Results:Disturbance resulted in an immediate displacement response of ~200 m (median).Air force disturbances tended to yield larger immediate responses than walker and,especially,than non-anthropogenic disturbances.Longer-term responses and immediate responses were approximately similar,suggesting that,over longer timescales,spatial disturbance effects in the study area remain confined to immediate effects.However,disturbances were infrequent (0.17 disturbances per bird per hour) and most disturbances were of natural origin (62%).Consequently, anthropogenic disturbance of roosting oystercatchers in the study area on average costs 0.08% of the daily energy expenditure. Conclusions:Our results suggest that immediate spatial responses to disturbance can be a useful proxy for spatial responses over longer timescales.Over the non-exhaustive range of conditions investigated,energetic consequences of spatial disturbance responses for an oystercatcher in the study area are marginal due to low disturbance levels.