Bird Damage to Pistachios

The extent of damage to pistachios by some birds that knock nuts to the ground, where they hull, shell, and eat them, can be measured. Losses to birds that pluck nuts from the tree and fly off to eat them else- where can only be estimated. counties to the south. District I1 (Central) is Merced, Madera, Fresno, and Kings Bird damage to nistachios counties. District I11 (Northern) is Monte- rey, San Benito, Inyo, and all counties to the north of Merced County. Terrell P. Salmon 0 A. Charles Crabb 0 RexE.Marsh Scope of the problem We received 105 responses (23 percent) from the 458 surveys mailed. Thirteen (12.7 percent) were excluded from analy- Crows are the primary culprits sis, because the orchards represented followed by ravens and jays were not in production, were outside Cali- fornia, or were managed by another per- son. The remaining 92 indicated they had pistachio losses due to one or more bird species. Bird damage was widespread throughout the state, as indicated by surveys returned from 18 counties. These 18 counties represent 98 percent of the bearing pistachio acreage in California. The infor- mation we report here is based on the survey returns and does not account for bird Various bird species are pests to a step in defining the problem and evaluat- damage and control that undoubtedly oc- number of California crops. Nut crops ing current bird control methods. cur but were not reported. Our estimates such as pistachios, almonds, and walnuts The major focus of the survey was to should therefore be considered conserva- are particularly hard hit, although infor- identify the bird species involved, the ex- tive. mation on actual losses is limited. Most tent and degree of damage, control meth- The survey included questions about damage occurs when birds feed on nuts or ods used, and their effectiveness. The six potential pest bird species with addi- knock them to the ground when landing in California Pistachio Commission mailed tional questions about birds unidentified trees. the survey to all 458 commercial pista- or not listed. Bird damage was reported Between 1975 and 1984,the acreage of chio growers in the state shortly after the to occur in orchards representing 22,460 bearing pistachios in California increased 1984 harvest. Ten days later, a follow-up of the 31,900 bearing acres (fig. 1). from about 600 to 31,900 acres, with a reminder was mailed to survey recipi- Growers reported the American crow corresponding increase in reported bird ents. We analyzed data using the SAS Sys- (Corvus brachyrhynchos) as the most fre- damage. We are conducting a study to tem on a VAX computer at the University quent pest bird of pistachios, followed by identify the bird problem, evaluate cur- of California, Davis. the Brewer’s blackbird (Euphagus cyano- rent control methods, and, to a limited de- For reporting purposes we grouped cephd[:sjand European starling (Sturnus gree, propose and test new damage con- counties into the three districts used by vulgaris), scrub jays (Aphelocoma coer- trol methods. A survey was mailed to the California Pistachio Commission. Dis- ulescens), common raven (Corvus corax), commercial pistachio growers as the first trict I (Southern) is Tulare County and all and yellow-billed magpie (Pica nuttalli]. CALIFORNIA AGRICULTURE, MAY-JUNE 1986 5 Eleven growers indicated they had dam- south. One grower reported raven damage caused by unknown or unidentified age in Yo10 County, which is within the birds. Some growers recognized bird bird's California range but appears to be damage, but were uncertain of the species an exceptional case of pistachio damage responsible. Others listed birds such as this far north. The raven normally knocks house finch (Carpodacus mexicanus), pistachios from the tree, then moves to sparrow (family Fringillidae), mourning the ground to hull, shell, and eat some of dove (Zenaida rnacroura), domestic pi- the pistachios that have fallen. Raven geon (Colurnba livia), and western mead- damage was calculated to cost just over owlark (Sturnella neglecta) as causing $900,000 (table 1).Most growers indicated damage in their orchards. that ravens were in the pistachio orchard From the results of the survey and our during its most susceptible period, hull- own field observations, it is clear that slip to harvest. most of the pistachio crop damage caused Crows were reported as pests of pista- by birds occurs during the six- to eight- chios by 79 percent of the survey respon- week period between the maturation of dents. We estimated that crows caused the first nuts (hull-slip) and harvest. slightly less than $800,000 damage to pis- To better assess the relative impor- tachios statewide. Crows feed on the nuts tance of pest birds to pistachio produc- either in the tree or on the ground after tion, we estimated the dollar loss caused knocking them from the tree. In areas by each species using the equation given where disturbance is likely, a crow will in the table 1 footnote. remove the nut from the tree and fly out of the orchard to feed in a less disturbed Bird damage location. Crows were most common in the Ravens were reported, with one excep- orchard from hull-slip to harvest, but tion, to damage pistachios only in the many remained after harvest. Some peo- southern region, from Tulare County ple suggest crows are beneficial after 11 am Unknown bird Scrub jays (top), magpies (center), and blackbirds (lower) ranked below crows and ravens as the most serious bird pests in Fig. 1. Distribution of pistachio production and bird damage by district. Each circle pistachio orchards. In total, birds caused represents 1,000 bearing acres. Blacked-out circles represent acreage of the orchards with $1.8 million in damage in 1984. some level of bird damage. 6 CALIFORNIA AGRICULTURE, MAY-JUNE 1986 harvest, because they remove mummy crow damage reported an increasing and hawk kites (kites that look like preda- nuts, a practice important in controlling problem in their pistachio orchards, tory birds). The observed effectiveness of naval orangeworm if present in the area. which they felt was due to higher numbers a control method varied with the bird spe- After-harvest feeding may further condi- of crows in the general area. A majority cies. tion the birds to use pistachios as food, of those indicating losses to scrub jays For ravens, over half of the growers however, creating a greater dependence also reported them as a growing problem using shooting rated it moderate to excel- on the orchard and crop the following because of increasing populations. It was lent (table 2). Av-Alarm and hawk kites year. not clear from the survey responses were reported so infrequently that conclu- Scrub jay damage to pistachios was re- whether magpies were becoming a more sions about their effectiveness are diffi- ported by 53 percent of the growers. serious problem, but none of the growers cult to draw. Scrub jays either hull, shell, and eat pista- with losses to these birds indicated that For crows, shooting was most fre- chio nuts in the tree or remove them from they were decreasing. The seriousness of quently used, and almost half of those us- the cluster and carry them from the or- the blackbird/starling problem, overall, ing this method reported a moderate level chard to either eat or cache in another did not appear to be changing. of control. Most growers using gas can- location. More than 14,000 acres of pista- nons reported slight to moderate control. chios were affected, and we estimate that Control methods used Most growers considered Av-Alarm and scrub jays caused just over $48,000 dam- The growers were asked to specify and hawk kites to be ineffective for crow con- age. While scrub jays occur in orchards rate the methods used, if any, to control trol. throughout the year, their numbers in- each bird species. All of the commonly Shooting was most effective in dispers- crease sharply from hull-slip to harvest. used control measures attempted to ing scrub jays. Gas cannons, Av-Alarm, or Magpies were reported to cause over frighten or disperse birds from the or- hawk kites offered slight or no control. $28,000 damage to pistachios. Reports of chard. Shooting was the most common, Shooting and gas cannons were the these losses came from only eight coun- followed by gas cannons (propane explod- only techniques used by more than one ties, all north of Madera County, fitting er), Av-Alarm (electronic noise maker). grower for controlling magpies. Most re- well with the bird's known geographical distribution. Much like crows in their TABLE 1. Damage by different bird species to pistachios reported by growers on the statewide feeding behavior, magpies feed on nuts in survey, 1984 the tree or knock them to the ground to Growers Average feed on them. Occasionally magpies Surveys reporting Area reported Estimated cache pistachio nuts. District returned damage affected loss loss' ~ ~~ Blackbirds and starlings were grouped Number $6 acres $/acre $ together, because it is difficult to distin- RAVEN guish between them in mixed flocks. Northern 19 5 200 12.19 2,439 Central 34 0 0 0 0 Blackbirds/starlings were the second Southern 39 33 9.848 92.34 909,364 most frequent bird reported to cause TOTAL 15 10,048 90.74 91 1.803 damage to pistachios, and they affected more acres than any other bird. In obser- CROW vations in pistachio orchards, we have Northern 19 79 578 6.42 3.71 1 Central 34 91 10.401 1.82 18,921 found blackbirds to be much more com- Southern 39 69 6,689 115.61 773,320 mon than starlings.

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