We used the apparatus designed by Webster and Lefebvre
(2001; see their Fig. 1) to assess innovative problem-solving
ability. A clear Plexiglas box (18 cm × 6.5 cm × 4.5 cm)
was filled with the birds’ usual seed mix. The birds could
open the box and obtain seeds by pulling or pushing the
middle drawer, pulling the two end drawers, or removing the
two lids; each lid and drawer was fitted with a metal ring. We
placed the box in the centre of the birds’ home cages for a
single 30 min trial, and recorded the latency to open the box
with the beak (modified from Webster and Lefebvre 2001). If
an individual did not open the box, we recorded the ceiling latency
of 1801 s. Birds were carefully monitored for accidental
openings with the wings or feet, but this never occurred.