  Individuals traversing challenging obstacles are faced with a decision: they
can adopt traversal strategies that minimally disrupt their normal locomotion
patterns or they can adopt strategies that substantially alter their gait,
conferring new advantages and disadvantages. We flew pigeons (Columba livia)
through an array of vertical obstacles in a flight arena, presenting them with
this choice. The pigeons selected either a strategy involving only a slight
pause in the normal wingbeat cycle, or a wings folded posture granting reduced
efficiency but greater stability should a misjudgment lead to collision. The
more stable but less efficient flight strategy was not employed to traverse
easy obstacles with wide gaps for passage, but came to dominate the postures
used as obstacle challenge increased with narrower gaps and there was a greater
chance of a collision. These results indicate that birds weigh potential
obstacle negotiation strategies and estimate task difficulty during locomotor
pattern selection.
