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Lesser-known vertebrate pests of almonds in California


During a three-year study to assess the effectiveness of broadcast distress calls on American crows (Corvus brachyrhynchos) in almond orchards, we had the opportunity to identify other vertebrate pests, some of which are not well documented. We describe the damage caused by these "lesser-known" species and in selected cases estimate the crop loss from these other pests in eight orchards in the Central Valley of California. In addition to crows and California ground squirrels (Spermophilus beecheyi), we recorded the presence of seven other vertebrate pests: scrub jays (Aphelocoma coerulescens), yellow-billed magpies (Pica nutalli), common ravens (Corvus corax), deer mice (Peromyscus spp.), western gray squirrels (Sciurus griseus), wild pigs (Sus scrofa), and beaver (Castor canadensis). Jays and magpies were found in six of eight orchards and caused damage of at least $56/ha at one site. Jays and magpies showed a preference for the soft-shelled Nonpariel variety of almond and tended to damage trees throughout the orchards, as opposed to concentrated damage along the edges. Ravens and wild pigs were found only in two Fresno County orchards located next to wildlands of the Coast Range Mountains. We could not specifically identify nor value damage by ravens as they may have reacted to the broadcast crow distress calls and abandoned the treated orchard. Nut loss from pigs amounted to $17/ha. Pig damage could be identified from tracks, broken branches, and the smashed appearance of damage nuts. Deer mice were the most serious pest in the two Fresno County orchards with damage of up to $51/ha. Signs of deer mouse damage included small, fine incisor marks around the edge of the hole in the nut, small shavings from the hull and shell, and a concentration of damaged nuts in the crotch of the tree and around the base of the trunk. Tree squirrels were the most serious pest in one orchard with damage of $46/ha. Tree squirrel damage was concentrated on particular trees in the orchard and damaged nuts were opened in a characteristic manner. Beavers felled almond trees at one orchard located next to a watercourse. We speculate the presence and abundance of a vertebrate pest relate to local habitat conditions, geographic location, the adaptability of species, and the dynamic nature of wildlife populations.

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