Western jackdaw amounts of silicaceous and calcareous grit to aid digestion of vegetable food and supply dietary calcium. Opportunistic and highly adaptable, the western jackdaw varies its diet markedly depending on available food sources. They have been recorded taking eggs and nestlings from the nests of the skylark ("Alauda arvensis"), Manx shearwater ("Puffinus puffinus"), razorbill ("Alca torda"), common murre ("Uria aalge"), grey heron ("Ardea cinerea"), rock pigeon ("Columba livia"), and Eurasian collared dove ("Streptopelia decaocto"). A field study of a large city dump on the outskirts of León in northwestern Spain showed that western jackdaws forage there in the early morning and
Trevor H. Worthy the Waitomo frog ("Leiopelma waitomoensis"). In the 1990s Worthy discovered several fossil bird species new to science, including the long-billed wren ("Dendroscansor decurvirostris") in 1991, Scarlett's shearwater ("Puffinus spelaeus") in 1991, and the Niue night heron ("Nycticorax kalavikai") in 1995. In 1991 he also described the Northland skink, a fossil skink species new to science. In 1998 Worthy excavated subfossil bones in Fiji, where he found remains of the flightless Viti Levu giant pigeon ("Natunaornis gigoura"), the Viti Levu scrubfowl ("Megapodius amissus"), the Viti Levu snipe ("Coenocorypha miratropica"), the giant Fiji ground frog ("Platymantis megabotoniviti"), and the small freshwater crocodile