Manufacture and use of hook-tools by New Caledonian crows

Extreme binocular vision and a straight bill facilitate tool use in New Caledonian crows

“…The curved bill characteristic of non-tool-using corvids 12 , on the other hand, results in significantly lower-elevation tool-projection angles (Table 1), which consequently raises the non-working end of the tool above the eye where it cannot be secured against the cheek. Tools held by NC crows are estimated to project 'above' the bill tip (note that, similar to visualfield parameters, sagittal tool-projection angles were measured against the line connecting the bill tip and eye, which provides an unambiguous reference; compare Figs 4a and 5), which is consistent with observations of natural tool-projection angles 5,9,10 . In contrast, tools held by all other investigated Corvus species would fall below the bill tip ( Fig.…”

“…New Caledonian crows Corvus moneduloides ('NC crows' hereafter) use tools for extractive foraging 5 , exhibiting a remarkable degree of dexterity. Using their bills, these tropical birds craft complex tools from sticks, leaf edges and other materials, before inserting them into deadwood or vegetation to 'fish' for invertebrate prey 6 .…”

Preliminary observations of tool-processing behaviour in Hawaiian crowsCorvus hawaiiensis

“…Our preliminary observations have confirmed that ‘Alalā are capable of modifying and manufacturing tools in a variety of ways, paving the way for dedicated experiments that systematically chart the species’ natural tool-making repertoire, as well as its ontogenetic development [4,22–24]. Importantly, subjects need to be tested under conditions where they have access to a wide variety of naturalistic foraging tasks (including those routinely encountered by wild New Caledonian crows [2,3,11,12,16]), and different plant materials for tool manufacture, but not to sticks or other objects that could be used as tools without further processing (as was the case in our first study [4]). This work programme, which we have recently launched, borrows experimental designs we developed for assaying the tool-manufacture behaviour of wild-caught New Caledonian crows [8,25–27].…”

“…Only a handful of bird species habitually make and use foraging tools [1], amongst them the well-known New Caledonian crow Corvus moneduloides [2,3]. Recently, we discovered that a second tropical corvid – the Hawaiian crow or ‘Alalā C. hawaiiensis – is a highly skilled, natural tool user [4].…”

“…New Caledonian crows also frequently engage in bark flaking (43% of recorded bill interactions in a study using bird-borne miniature video cameras [11]), and exhibit a wide range of tool-processing behaviours [2,3,8,11–18], but to our knowledge, there have been no reports of bark tool use in the wild. Interestingly, the only observation to date of a wild American crow C. brachyrhynchos using a tool for (presumed) extractive foraging involved the use of a wooden splinter, which the bird had released from a fence post through pecking and pulling [19].…”