Nasal saddles reduce survival rate in Eurasian teal

Abstract Nasal marks are used to study duck behavior and demography. Earlier tests detected no negative effects on dabbling duck physiology and behavior, but the potential deleterious effect on annual survival probability remained to be evaluated. We relied on multistate capture‐mark‐recapture models applied to 11,874 Eurasian teal ( Anas crecca ) banded in France from 2002 to 2021, of which 308 were recaptured alive at least once and 1,390 yielded dead band recoveries. Of the banded individuals, 6,770 teal (57.0%) were also marked with a plastic nasal saddle to evaluate the cost‐benefit trade‐off of the technique. Saddled teal had a lower annual survival probability (ranging from 0.30 ± 0.02 [SE] in hatch‐year females to 0.45 ± 0.02 in after hatch‐year males) than banded‐only individuals (0.44 ± 0.03 to 0.53 ± 0.02). Incorporating live nasal saddle resighting information in life histories of the individuals did not improve precision of annual survival probability estimates. The mechanism behind such reduced annual survival remains unclear, and a potential greater influence of hunting on saddled birds cannot be excluded, either through greater exposure to hunting owing to birds’ behavior or through greater targeting by hunters. In any case, there were clear drawbacks to bird survival, with very limited benefits for the biologists, so this technique should be abandoned when the unique goal of fitting nasal saddles is to evaluate long‐term demographic parameters in dabbling ducks. The method could remain valuable for other purposes such as shorter‐term monitoring of brood‐rearing females, evaluation of stopover duration, or some migration studies, but even then, results should be interpreted with caution and animal welfare issues should be considered.