No Evidence for Sparrowhawks Selecting Redshanks According to Size or Condition

Abstract

During a 10-year study at two adjacent Scottish sites we tested the null hypotheses that Sparrowhawks Accipiter nisus selected overwintering Redshanks Tringa totanus independently of body size and condition. There was no significant difference in wing length, leg length and bill length between Redshanks killed by Sparrowhawks and the Redshank population as assessed from cannon-netted samples. On one site in one winter the survivors (where 20% of the surviving population was sampled) were no different in size from those killed by Sparrowhawks (where over 45% of the wintering population was killed), although shorter-legged adults were killed more frequently than expected. There was no significant variation in the size of Redshanks killed by Sparrowhawks with month. Redshanks maintained the same body condition relative to other Redshanks throughout a winter. The body condition of Redshanks killed by Sparrowhawks was not different from that of Redshanks cannon-netted at the same time of winter, and there was no suggestion that birds in either particularly poor or particularly good condition were selected. The lack of selection according to size or condition was probably due to Sparrowhawks being surprise, short-chase predators that selected prey on the ground.