Ringing or colour-banding does not increase predation mortality in redshanks Tringa totanus

Abstract

The use of metal and colour-rings or bands as a means of measuring survival, movements and behaviour in birds is universal and fundamental to testing ecological and evolutionary theories. The practice rests on the largely untested assumption that the rings do not affect survival. However this assumption may not hold for several reasons, for example because the ‘oddity effect’ predicts predators select prey that appear different to their neighbours in order to avoid the ‘confusion effect’. We compared the foraging behaviour and the death rates of redshanksTringa totanusconspicuously marked with six colour rings and one metal ring each to unmarked birds in a study system, where routinely up to 50% of the total population are killed by avian predators during a winter. If avian predators selectively target and/or have a higher capture success of ringed birds then we would predict the proportion of colour-ringed birds in the population to decline through a winter. The proportion of colour-ringed birds in the population did not change over the course of three separate winters, and in one winter the ratio of marked:unmarked birds found killed by sparrowhawksAccipiter nisuswas the same as the ratio of marked birds alive in the population. In the year with largest sample size, power was sufficient to detect a greater than 2.2% difference in predation rate between ringed and unringed groups. The average kill rate difference between ringed and unringed birds across the three winters was less than 1% (0.73±2.2%) suggesting that even if there were differences in predation rate that were not detected because of low statistical power they were extremely small. There were no differences in any foraging measures comparing ringed and unringed birds, suggesting that the rings did not affect the ability of birds to meet their daily energy budgets. The results showed that colour-ringed birds were not preferentially targeted or killed by avian predators, and suggest that the presence of a metal and even several large colour-rings is unlikely to affect behaviour and predation mortality even under extreme selection.