Parrot sound tool design: drum tool data

The rarity of tool manufacture in wild parrots is surprising because they
share key life history traits with advanced tool-using species including
large brains, complex sociality, and prolonged parental care. When it does
occur, tool manufacture in parrots tends to be innovative, spontaneous and
individually variable but most cases have been in captivity. In the wild,
only palm cockatoos (Probosciger aterrimus) have been observed using tools
regularly. However, they are unusual because they use tools to enhance
their displays rather than for foraging or self-maintenance. Males in
northern Australia make two types of tool from sticks and seed pods, which
they tap rhythmically against a tree during display. We analysed 256 sound
tools retrieved from 70 display trees. Drum sticks (89% of tools) were
used more often than seed pod tools; most males manufactured only
drumsticks, but some made both types. Individual males differed
significantly in the design of their drumsticks including the length,
width and mass, but we found no evidence that neighbours copied each
other. We discuss the highly individualised preferences for sound tool
design in context of the behavioural predispositions behind the rarity of
tool manufacture in wild parrots.