Weir, A.A.S., Chappel, J. and Kacelnik, A. (2002) Shaping of Hooks in New Caledonian Crow. Science, 297, 981.
http://dx.doi.org/10.1126/science.1073433

has been cited by the following article:

• TITLE: What a Parrot’s Mind Adds to Play: The Urge to Produce Novelty Fosters Tool Use Acquisition in Kea

  AUTHORS: Gyula K. Gajdon, Melanie Lichtnegger, Ludwig Huber

  KEYWORDS: Animal Cognition; Tool-Use Behaviour; Object Play; Object Exploration; Animal Innovation

  JOURNAL NAME: Open Journal of Animal Sciences, Vol.4 No.2, March 28, 2014

  ABSTRACT: Motivational and cognitive aspects of spontaneous tool-use acquisition in species that do not do so habitually, remain an open but most relevant question. To address this, we studied captive kea (Nestor notabilis), New Zealand mountain parrots renowned for their playful cleverness. The majority of adolescent, but not the adult kea, showed a toddler-like motivation to insert objects into empty tubes and also spontaneously used objects in order to eject food from inside a tube. This parallel what is known from object exploration in large brained mammals and shows for the first time in a habitually non-tool using bird that such a technical innovation is based on object-combining acquired outside the foraging context.