| Abstrakt: |
Birds can be unintentionally injured or killed by mammal traps. Unfortunately, some birds in Hawai‘i, including puaiohi (Myadestes palmeri), and in New Zealand, have been killed by the widely used Goodnature® A24 rat-stoat self-resetting trap (A24s) during rodent control. To help address this problem, we conducted two sets of aviary trials using (1) barriers and (2) existing A24 excluders with red-winged blackbirds (Agelaius phoeniceus), European starlings (Sturnus vulgaris), and a single puaiohi. We conducted barrier trials to inform future bird excluder designs by establishing the minimum gap-height beneath a barrier that blackbirds and starlings successfully overcome. During barrier trials, starlings defeated barriers significantly lower (≥ 1.9 cm) than blackbirds (≥ 2.9 cm). We then presented disarmed A24s with no excluder or with one of two excluders (plastic Goodnature, 11 cm length; and metal mesh, 10 cm, or 15–17 cm length for puaiohi) to each bird species. We placed the A24s and excluders low (11–25 cm trap height, 0–10 cm excluder height) and high (50–83 cm trap height, 37–72 cm excluder height) above ground to test bird entry abilities at trap heights used by land managers to control rodents. During the A24 excluder trials, all three bird species entered the trap at low or high heights with no excluder, confirming bird risk of injury when excluders aren’t used. Excluders greatly decreased entry into A24s by blackbirds and puaiohi, but not by starlings. Plastic and metal excluders prevented puaiohi entry at low height only. Based on our trials and recent field uses, the plastic excluder performed best for excluding all three bird species if placed so the lower edge of the excluder is 0–2 cm above ground. However, plastic and metal excluders can clog with dead rodents when positioned low. Future trials aiming to exclude all small birds from A24s while maintaining trap efficacy against target rodents should consider new excluder designs incorporating the 1.9–2.9 cm gap-height thresholds. When deciding whether to use excluders and appropriate trap heights, managers need to consider both the risk of non-target injuries or deaths and the impact of potentially decreasing trap efficacy. [ABSTRACT FROM AUTHOR] |
