For many aquatic and semiaquatic mammal, amphibian and fish species, environmental DNA (eDNA) methods are employed to detect species distribution and to monitor their presence, but eDNA is much less employed for avian species. Here, we developed primers for the detection of true geese and swan species using eDNA and optimized a PCR protocol for eDNA. We selected taiga bean goose (Anser fabalis fabalis) as our focal (sub)species and sampled water from lakes, from which the presence of taiga bean goose was visually confirmed. We filtered the lake water and extracted eDNA. We also included field negative controls (sterile water) which were handled similarly as eDNA samples to control sterility of equipment. For testing if taiga bean goose DNA could be detected among DNA of other goose species, we similarly sampled eDNA from a zoo pond housing several Anatidae species. We were able to detect taiga bean goose DNA in all but one of the tested lakes, including the zoo pond. The primers developed are not species-specific, but rather specific for the genus Anser, due to close relatedness of Anser species. We also developed eDNA primers for Branta-species and Cygnus-species and tested these primers using the same samples. Canada goose (B. canadensis) and barnacle goose (B. leucopsis) DNA were only detected in the zoo pond (in which they were present), as the sampled natural lakes fall outside the range of these species. We detected whooper swan (C. cygnus) DNA in three lakes and the zoo pond (in which the species was present). The eDNA method presented here provides a potential means to monitor elusive goose species and to study the co-occurrence of large waterfowl.

Telomere length is increasingly used as a biomarker of long-term life history costs, ageing and future survival prospects. Yet, to have the potential to predict long-term outcomes, telomere length should exhibit a relatively high within-individual repeatability over time, which has been largely overlooked in past studies. To fill this gap, we conducted a meta-analysis on 74 studies reporting longitudinal telomere length assessment in non-mammalian vertebrates, with the aim to establish the current pattern of within-individual repeatability in telomere length and to identify the methodological (e.g. qPCR/TRF, study length) and biological factors (e.g. taxon, wild/captive, age class, species lifespan, phylogeny) that may affect it. While the median within-individual repeatability of telomere length was moderate to high (R = 0.55; 95% CI: 0.05-0.95; N = 82), marked heterogeneity between studies was evident. Measurement method affected strongly repeatability estimate, with TRF-based studies exhibiting high repeatability (R = 0.80; 95% CI: 0.34-0.96; N = 25), while repeatability of qPCR-based studies was only half of that and more variable (R = 0.46; 95% CI: 0.04-0.82; N = 57). While phylogeny explained some variance in repeatability, phylogenetic signal was not significant (λ = 0.32; 95% CI: 0.00-0.83). None of the biological factors investigated here had a statistically significant association with the repeatability of telomere length, being potentially obscured by methodological noise. Our meta-analysis highlights the need to carefully evaluate and consider within-individual repeatability in telomere studies to ensure the robustness of using telomere length as a biomarker of long-term survival and fitness prospects.