Hearing that loud ‘caw caw caw’ sound in your pistachio orchard can be a signal that one of the most destructive bird pests has invaded.
Scare tactics including rotating distress calls, cannons and gunfire have been standard procedure to convince crows to feed elsewhere. Now, new drone technology may offer improved crop protection.
There are several bird species that can cause substantial crop damage by feeding on developing nuts in almond and pistachio orchards, but crows have nested as the primary bird pest due to their size and habits. In almond orchards, crows will start feeding in the early summer months before, during and after hull split. In pistachio orchards, they feed close to harvest, knocking nuts on the ground and feeding on them. Studies show that a single crow can consume up to a pound and a half of nuts per day from the time of hull split through harvest. Growers report that crows knock even more nuts to the ground than they eat. Crows congregate in large flocks, making their control in orchards difficult, according to guidelines published on University of California Integrated Pest Management program website.
Know Your Birds
With any pest bird species, identification is critical to determine its status and if a depredation permit is required. No permit or depredation order is required for starlings or crows. For crows, the owner or manager must verify the crop damage is due to crows and that a non-lethal means of removal has been tried first. If a legal take occurs, the owner or manager is required to document the take and report it to the Regional Migratory Bird Permit office. Details of this requirement can be found on the Vertebrate Pest Control Research Advisory Committee website vpcrac.org.
According to the Pistachio Production Manual, early morning is the best time to monitor for crow movement or other pest bird feeding. Observing flock movement and noting numbers can help determine probability of crop loss or damage. Watching for bird movement into or within a field, roosting sites and identification of species is advised. Inspection for bird damage in the developing nut crop is also important.
Quality and frequent observations are needed to identify pest birds before their populations increase and damage is done.
Crows, Corvus brachyrhynchos, are large, black birds with black bills and feet. They fly and feed in large numbers, following their scouts into favored feeding areas.
California Fish and Wildlife regulations allow crows to only be taken by landowners or tenants where it is proven they have caused crop damage. Shooting, however, has not been the most successful control method, in part due to time and labor involved. It can be an early intervention strategy, by sending crows elsewhere to feed before they have formed the habit of coming into your orchard.
Crows can adapt readily to control measures and human activity, meaning distress signals and propane cannons need to be changed or moved frequently to remain effective. Scout birds in the flock will identify food sources and then return to the roost to lead the rest back to feed. If scout birds can be deterred, they will lead the rest of the flock to another location. Crows will fly up to 20 miles from their roost to feeding areas.
Another potentially destructive bird species, European starlings, are an invasive bird species with a wide habitat range. They do not feed on nuts, but congregate in trees in large numbers and their droppings can contaminate the crop. These dark colored birds are 7 to 8 inches long and have speckling on feathers. Their bills are yellow during the summer and darken in the winter. As an invasive species, they can be lethally taken at any time.
Scrub-jays, magpies, sparrows and house finches are also listed as possible pest species. They feed in smaller numbers, but can congregate in larger flocks when orchards are located near perennial thick vegetation. Sparrows and house finches can damage fruit buds during the dormant season, leading to loss of production.
Evaluating Drones
Dr. Page Klug, Supervisory Research Wildlife Biologist with the USDA National Wildlife Research Center at the North Dakota Field Station, has conducted evaluations of unmanned aircraft systems as a tool to protect agricultural crops from bird damage.
UAS are known to elicit behavioral and physiological responses in wildlife and have been proposed as a means to protect crops from birds. Klug evaluated behavior responses of blackbirds to fixed wing and rotary wing drones. The UAS platforms used in the study were Fourthwing Vireo (fixed wing) and the DJI Inspire and different hazing approaches were tested.
The birds showed no response to the fixed wing UAS, but did show a response to the rotary UAS and responses were more pronounced with lower altitude approaches. Klug concluded that the rotary UAS has the potential to modify bird behavior in a way that may reduce crop damage, but emphasized in her research that no studies have been done to assess potential effectiveness.
Klug said that to be effective in protecting crops from blackbird depredation, modifications to the physical UAS might be needed. Modifications include addition of an audio system to produce distress or alarm calls or firearm discharge sounds, adding lasers or lights or shapes that mimic an aerial predator.
In addition, a fully automated UAS may be a more effective strategy. This modification could potentially reduce labor, Klug wrote. The UAS could also be programmed to fly patterns which would be most likely to deter birds. Environmental conditions also come into play with UAS use as low temperatures can affect battery packs. Klug noted that their evaluations were done with specific UAS models and other types of drones and responses by birds to approaching UAS can vary based on the specific platform and are likely species and context specific.
While understanding the efficacy of drones may be a way off, they offer one more potential tool in an arsenal required to outwit bird pests in nut crops.
