Project Accomplishments

Project Accomplishments


Methods Development and Population Biology of Blackbirds and Starlings in Conflict with Agriculture, Concentrated Animal Feeding Operations, and Urban Environments

PROJECT GOAL: To develop new and scientifically valid methods to reduce blackbird and starling damage to ripening sunflower crops, feedlots, and dairies.

Project Accomplishments 2010

Wildlife cause significant damage to agricultural resources and property in the United States. A survey conducted by USDA's National Agricultural Statistics Service (NASS) reported wildlife damage to U.S. agriculture at $944 million during 2001 (the most recent year available). Field crop losses to wildlife totaled $619 million, and losses of vegetables, fruits, and nuts totaled $146 million. Blackbirds, starlings, geese, and other birds are a primary cause of damage to grain and fruit crops. Starlings and blackbirds also consume livestock feed and potentially transmit diseases in urban areas and feedlots. National Wildlife Research center (NWRC) scientists are studying ways to refine current damage abatement methods and develop new methods for reducing bird depredation on seeded and ripening sunflower, corn, and rice.

photo of sunflowersBird Damage to Corn and Sunflower in North Dakota— North Dakota is the top sunflower producer in the United States, harvesting about 1 million acres annually. Red-winged blackbirds, common grackles and yellow-headed blackbirds cause significant damage to this crop. The last comprehensive field survey of bird damage to sunflower in the State, conducted in 1979 and 1980, indicated that bird depredations resulted in average annual economic losses of almost $5 million to North Dakota sunflower growers. The losses are probably even greater today, as sunflower prices have increased appreciably since this survey was conducted. There has also been an increase in complaints about bird depredations from corn growers, as acreages of this crop have increased in North Dakota during recent years. However, quantitative surveys of blackbird damage to corn have never been conducted in the State. A current survey of bird damage to both sunflowers and corn (many growers plant both crops) could be useful for allocating resources to manage depredating blackbird populations and plan perennial sunflower planting locations.

In 2008, NWRC researchers surveyed blackbird damage to sunflower and corn crops in the Prairie Pothole Region, the principal corn and sunflower growing area in North Dakota. Despite a reduction in planted sunflower acres from approximately 2 or 3 million acres in 1979 and 1980 to about 1 million in 2008, the percentage of loss due to bird damage in sunflower crops was nearly identical between the 2008 survey and the 1979/1980 surveys. In 1979 to 1980, damage averaged 1.4% (range = 0.0 to 26.4 percent) over approximately 2.8 million acres, whereas the 2008 damage averaged 1.2% over approximately 1 million acres. The researchers found that birds damaged approximately 0.7% (range = 0.0 to 9.5%) of the 2 million acre corn crop in 2008. Based on these findings, the researchers speculated that corn—which was not commonly available to the blackbirds 30 years ago in North Dakota—served as an alternative food source for the birds. Additionally, growers might have benefited from APHIS Wildlife Services' cattail management program, which was implemented in the early 1990s to thin cattail stands and thereby disperse blackbird roosts away from sunflower fields.

Anthraquinone-Based Bird Repellent for Sunflower Crops—NWRC scientists continue to explore nonlethal alternatives for managing bird damage to confectionary and oilseed sunflower crops. Ring-necked pheasants ( Phasianus colchicus) and blackbird species are of particular concern due to the extensive localized damage they cause to newly-planted and ripening sunflower crops. NWRC scientists conducted several laboratory and field studies to determine whether an anthraquinone-based repellent can decrease bird depredations to seeded and ripening sunflowers.

Prior to testing the repellency of Avipel® repellent (50% 9,10-anthraquinone), NWRC scientists determined that the product did not hinder germination rates of confectionary and oilseed sunflower seeds. In preference tests with captive birds, pheasants avoided seedlings derived from anthraquinone-treated seeds. Grackles ( Quiscalus quiscula) avoided anthraquinone-treated sunflower seeds in cage trials and in penned enclosure trials. In cage trials, grackles avoided treated seeds in a dose-dependent manner. These trials showed an 80% repellency rate for confectionary sunflower seeds at a concentration application rate of 9,200 parts per million (ppm) anthraquinone (Avipel). Penned enclosure trials confirmed the utility of Avipel as a repellent for grackles. Enclosures containing ripening confectionary sunflower treated with Avipel sustained 18% damage compared to 64% damage for the enclosure containing untreated crops. The biomass of seeds harvested from treated enclosures averaged 2.54 kilograms (dry weight) compared to 1.24 kilograms among untreated enclosures. These tests suggest that anthraquinone-based repellents may be effective in preventing blackbird damage to sunflowers and result in increased yields for Avipel-treated crops.

Use of Anthraquinone To Alleviate Nontarget Take From Rodenticides—Rodenticides are a key component for crop protection, and reducing nontarget exposure to rodenticides is an important consideration in the maintenance of existing pesticide labels and the development of new products. In an effort to reduce the nontarget risk associated with rodenticides, NWRC scientists explored the possibility of adapting a currently registered bird repellent (anthraquinone) for incorporation into these materials.

The results of this study showed that adding an anthraquinone repellent prevents the consumption of rodenticide baits by Canada geese ( Branta canadensis) and ring-necked pheasants ( Phasianus colchicus) . Captive geese avoided baits treated with 2% zinc phosphide (typical concentration level used in rodenticide applications) and 2% to 2.5% anthraquinone (Arkion® Life Sciences). Although some geese and pheasants initially sampled treated baits, all birds subsequently avoided treated baits. No mortality or signs of zinc phosphide poisoning were observed among 10 geese and 40 pheasants that were offered the repellent-treated zinc phosphide baits.

Additional NWRC studies are underway to evaluate the efficacy of the new anthraquinone-zinc phosphide bait for target rodent species. NWRC researchers also plan to investigate possible uses of this new bait in reducing nontarget hazards with other pesticides, to compare costs relative to expected damage at unmanaged sites, and to assess the bait's environmental impacts.

photo of acorn woodpeckerWoodpecker Deterrent for Utility Pole Crossarms— Woodpeckers cause millions of dollars in damage to wooden utility pole structures around the world by pecking or drumming at the structures when searching for insects, announcing their territory, or excavating nesting or roosting cavities. The resulting damage presents a safety hazard to utility workers, promotes decay (due to water entrapped in the holes), necessitates premature replacement, and can lead to collapse under adverse conditions. In the United States, pileated woodpeckers (Dryocopus pileatus) cause some of the most severe damage to poles.

During studies of captive pileated woodpeckers, NWRC researchers evaluated the effectiveness of a polyurea elastomer coating material (applied in a process developed by Brooks Manufacturing Company in Bellingham, WA) for eliminating or reducing woodpecker damage. The company supplied coated, Douglas-fir crossarms that measured 8.5 x 11 centimeters wide and 243 centimeters long. In the study, researchers presented 18 pileated woodpeckers (which were captured and later returned to national forests in Missouri and Arkansas) with coated and uncoated crossarms for 10 days. Researchers recorded daily the dried weight of wood chips removed; the length, depth, and area of damage; and the condition of the coating on the crossarms. Woodpeckers removed an average of 29.5 grams of wood chips from non-coated crossarms, but caused no measurable damage to the fully coated crossarms.

The cost of an uncoated wood crossarm is approximately $22 to $35, compared to approximately $65 to $120 for a fiberglass composite crossarm. The cost of a wooden crossarm with protective polyurea elastomer ranges from $52 to $80, which is less or comparable to the cost of crossarms made of fiberglass composites or other resistant materials on the market. However, additional research is needed to determine whether coated wood crossarms are more cost effective than other materials over the lifetime of the utility structure.

Movements and Site Use of Rural and Suburban European Starlings—NWRC researchers tracked the movements and habitat use of European starlings radio tagged in central New Jersey during December 2009. The study area was a mosaic of rural and suburban land features, including three photo of tagging of European starlingstudy sites—a game bird facility and two dairies. The sites were separated by an average of 40 kilometers.

By late December, a majority of the radio-tagged birds at the game bird facility had either abandoned or severely limited use of the facility. The researchers speculate that the birds stopped coming to the site after the facility switched from a meal-based food to whole kernel corn. Even though use of the study site declined, the cohort remained within 15 kilometers of the study site.

Of the two diaries, one was embedded within a suburban area, whereas the other was in a predominately rural area. The dairies were used differently by the starling cohorts. The rural dairy received more consistent and intensive use than the suburban-embedded dairy. The differences also extended to roosting behavior, with the rural dairy being a favorite roosting site of its cohort, whereas the suburban-embedded dairy was never used for roosting. Starlings in suburban areas typically roosted in the dense vegetation of evergreen stands or in low-lying areas with wetland emergents (e.g., Phragmites spp. and Typha spp.).

Compared to the rural group, turnover rates at suburban roosts were higher, resulting in less cohesive roosting congregations. The difference in behaviors between rural and suburban starlings was probably related to increased habitat diversity in the suburban environment, which decreased daily site fidelity and increased sporadic use of small satellite roosts lying near major roost sites. By contrast, starlings in the rural environment existed in a rather homogenous landscape that consisted of large portions of infrequently used habitats. The used habitats were isolated and island-like, perhaps promoting greater site fidelity to daytime sites and roosts. (Note: The researchers do not consider the observed dichotomous behavior to be an anomalous result of this study, as they have had results similar to these in five other radio telemetry studies in rural study areas [Texas, Kansas, and Ohio] and suburban-urban areas [Indianapolis, IN, and Omaha, NE]).

The results of this study provide useful information for those tasked with lethally managing populations of nuisance starlings in suburban-urban areas using DRC-1339. Because the product is a slow-acting avicide, birds usually fly away from the bait site and, in suburban environments, can die in a wide array of habitats where they are difficult to find. Therefore, prior to baiting with DRC-1339, managers should know the general directions of arriving and departing flight lines that may provide an approximate bearing to the roosting site where their carcasses can be recovered.

Bioenergetics Model for European Starlings—DRC-1339 is an avicide registered for use with European starlings ( Sturnus vulgaris) to protect agricultural crops, feedlots and dairies, and other resources. To better estimate starling mortality during DRC-1339 baiting operations, NWRC scientists developed a bioenergetics model. The model uses environmental variables and avian characteristics to estimate metabolic energy demands of individual starlings and then generates a mortality estimate based on the total number of treated baits eaten and DRC-1339 toxicity.

To verify that the model makes realistic estimates of daily metabolic rates during varying environmental conditions, the scientists compared predictions from the model with actual energy requirements associated with the maintenance metabolism of caged starlings held outdoors during a 12-day feeding trial in Kansas. A broad range of temperatures (­17 to 14° C), wind speeds (0 to 40 kilometers per hour), and percent cloud cover (0 to 100%) were encountered during the trial. Daily feeding rates of caged starlings indicated that metabolic rates ranged from 157 to 305 kilojoules per bird per day, compared to 208 to 274 kilojoules per bird per day predicted by the bioenergetics model. There was no significant difference between the bioenergetics model estimates of daily metabolic rate when compared against estimates generated in the feeding trial.

The bioenergetics model produced robust predictions under varying meteorological conditions typical of winters in the interior United States. Thus, the model can be used to estimate starling mortality under the wide variety of conditions where DRC-1339 is used to reduce populations of this species.

Evaluating Handheld Lasers To Disperse Roosting Blackbirds—Red-winged blackbirds, yellow-headed blackbirds, and common grackles cause an estimated $15 million worth of damage to sunflowers in North Dakota and South Dakota each year. Many blackbird populations roost in wetland areas near sunflower fields, and wildlife managers need a cost-effective, user-friendly method for dispersing birds from roosts in these areas. To help address this issue, NWRC researchers tested the effectiveness of moderately-powered red and green lasers for dispersing blackbirds roosting in a cattail marsh. Preliminary results showed no significant differences among the control (non-laser), red laser (650 nanometers) and green laser (520 nanometers).

Evaluation of Large, Mobile Decoy Traps for Managing Blackbirds—Each year, an estimated 75 million blackbirds migrate through the sunflower-growing regions of the Great Plains and cause severe damage to ripening sunflower and corn. It is important for wildlife managers to have effective options available to control blackbird populations and protect the region's crops from damage.

In a recent study, NWRC scientists evaluated large, mobile decoy traps for capturing blackbirds that were damaging or preparing to cause damage to sunflower fields in North Dakota. Over a period of 1 month, researchers captured 154 red-winged blackbirds (from an estimated population of 15,000) in two decoy traps. All of the birds were captured in the last two weeks of the study—after the sunflower crops had reached physiological maturity and become slightly less palatable or harder to open. In this regard, the traps did not reduce blackbird depredation on the sunflowers. Researchers concluded that large decoy traps are not cost effective because of the high labor and travel costs associated with maintaining decoy birds and the relatively few numbers of captured free-ranging blackbirds. The results of this study corroborate those obtained by researchers in Canada and suggest that decoy traps would not be an effective component of an integrated bird management plan to protect ripening sunflowers.

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