Damage and Damage Identification

European starling, Sturnus vulgaris

Starlings are frequently considered pests because of the problems they cause, especially at livestock facilities (Fig. 3) and near urban roosts. Starlings may selectively eat the high-protein supplements that are often added to livestock rations.

Figure 3. At livestock facilites such as this pig operations, European starlings consume feed, contaminate feed and water with their droppings, and may transmit disease.

Starlings may also be responsible for transferring disease from one livestock facility to another. This is of particular concern to swine producers. Tests have shown that the transmissible gastroenteritis virus (TGE) can pass through the digestive tract of a starling and be infectious in the starling feces. Researchers, however, have also found healthy swine in lots with infected starlings. This indicates that even infected starlings may not always transmit the disease, especially if starling interaction with pigs is minimized. TGE may also be transmitted on boots or vehicles, by stray animals, or by infected swine added to the herd. Although starlings may be involved in the spread of other livestock diseases, their role in transmission of these diseases is not yet understood.

Starlings cause other damage by consuming cultivated fruits such as grapes, peaches, blueberries, strawberries, figs, apples, and cherries. They were recently found to damage ripening (milk stage) corn, a problem primarily associated with blackbirds. In some areas starlings pull sprouting, grains, particularly winter wheat, and will eat the planted seed. Starlings may damage turf on golf courses as they probe for grubs, but the frequency and extent of such damage is not well documented.

The growing urbanization of wintering starling flocks seeking warmth and shelter for roosting may have serious consequences. Large roosts that occur in buildings, industrial structures, or, along with blackbird species, in trees near homes are a problem in both rural and urban sites because of health concerns, filth, noise, and odor. In addition, slippery accumulations of droppings pose safety hazards at industrial structures, and the acidity of droppings is corrosive.

Starling and blackbird roosts located near airports pose an aircraft safety hazard because of the potential for birds to be ingested into jet engines, resulting in aircraft damage or loss and, at times, in human injuries. In 1960, an Electra aircraft in Boston collided with a flock of starlings soon after takeoff, resulting in a crash landing and 62 fatalities. Although only about 6% of bird-aircraft strikes are associated with starlings or blackbirds, these species represent a substantial management challenge at airports.

One of the more serious health concerns is the fungal respiratory disease histoplasmosis. The fungus Histoplasma capsulatum may grow in the soils beneath bird roosts, and spores become airborne in dry weather, particularly when the site is disturbed. Although most cases of histoplasmosis are mild or even unnoticed, this disease can, in rare cases, cause blindness and/or death. Individuals who are weakened by other health conditions or who do not have endemic immunity are at greater risk from histoplasmosis.

Starlings also compete with native cavity-nesting birds such as bluebirds, flickers, and other woodpeckers, purple martins, and wood ducks for nest sites. One report showed that, where nest cavities were limited, star-lings had severe impacts on local populations of native cavity-nesting species. One author has speculated that competition with starlings may cause shifts in red-bellied woodpecker (Melanerpes carolinus) nesting from urban habitats to rural forested areas where starling competition is less.

Economics of Damage and Control

Consumption of livestock feed by starlings can at times be a substantial economic consideration. Data reported in 1968 from Colorado feedlots estimated the cost of cattle rations consumed during winter by starlings at $84 per 1,000 starlings. Current feed costs and the associated losses would certainly be much higher. A 1967 report indicated that 1 million starlings at a California feedlot resulted in losses of $1,000 per day because of food consumption and contamination, and starling interference with cattle feeding activity. Another report estimated that starlings in Idaho consumed 15 to 20 tons (13.5 to 18 mt) of cattle feed per day. A 1978 study in England estimated that the food eaten by star-lings in a calf-rearing unit over three winters was 6% to 12% of the food presented to the calves. Two other studies in England since then found 4% losses and negligible damage, respectively. Producers who wish to estimate feed losses to starlings at their facilities can do so using one of two methods. The following equation, which was developed from data in Colorado, estimates the cost of feed consumed per day:

Cost of feed ration consumed per day = estimated starlings (to the nearest 1,000) x fraction of birds using trough x cost of feed ration per pound (0.4536 kg) x 0.0625 pound (0.02813 kg) consumed per starling per day.

A second method, which may be applicable to most geographic areas, precludes the need of estimating star-ling populations. It requires the operator to observe the feed troughs several times during the day and estimate the number of starlings entering the troughs per day. From this estimate the cost of the feed ration consumed per day can be estimated with the following equation:

Cost of feed ration consumed per day = estimated starling entries into troughs x 0.0033 pounds (0.0015 kg) consumed per starling entry x cost of feed ration per pound (0.4536 kg).

These losses projected over a 3-to 4-month damage season can assist in evaluating the costs and benefits of proposed control measures.

Feed contamination from starling excreta may not be an economic loss for cattle or pig operations. In 2 years of testing at Western Kentucky University, neither pigs nor cattle were adversely affected by long-term exposure to feed heavily contaminated with starling excreta. As compared to controls, no significant differences were observed in weight gain or feed efficiency (ratio of weight gain to weight of feed offered). In addition, there were no observed differences in feed rejection or disease incidence. These results indicate that there is no economic justification for starling control based solely on feed contamination. However, the effects of livestock water contamination from starling excreta have not been well studied.

Starling interference with livestock feeding patterns may have economic importance. A study in England reported that calves in pens protected from starlings showed higher growth rates and better feed conversion than those in unprotected pens. This protection led to an increased profit margin. The difference observed, however, might have been caused by starlings in the unprotected pens consuming the calf food, especially the high protein portion, rather than by actual interference with the calf feeding.

The costs associated with starlings in the spread of livestock disease may at times be substantial. For example, during the severe winter of 1978-1979, a TGE outbreak occurred in southeast Nebraska, with over 10,000 pigs lost in 1 month in Gage County alone. Starlings were implicated because the TGE outbreak was concurrent with large flocks of starlings feeding at the same facilities. More recent data show that starlings are capable of carrying this disease in their feces. The role of starlings in disease transfer, however, needs further study.

Bird damage to grapes in the United States was estimated to be at least $4.4 million in 1972; starlings were one of the species causing the most damage. Starlings, as well as many other species of birds, also damage ripening cherry crops. A 1972 study in Michigan found 17.4% of a total crop lost to birds. A 1975 study in England estimated damage at 14% (lower branches) to 21% (tree canopy) of the crop; similar 1976 data showed less damage. Starling damage to winter wheat in a study of 218 fields in three regions in Kentucky and Tennessee averaged 3.8%, 0.5%, and 0.4% respectively, with the most serious losses (more than 14%) occurring where wheat was planted late and fields were within 11 miles (16 km) of a large star-ling roost.

Human health and safety problems associated with urban starling roosts include concerns about the disease histoplasmosis and about aircraft-bird collisions. Although serious problems occur only infrequently, they can have grievous consequences where loss of human life and/or permanent disability may occur. Moreover, equipment repair and replacement costs associated with aircraft-bird collisions can be substantial. For example, the costs of aircraft-bird collisions in the United States are estimated to be at least $20 million per year to commercial aircraft and $10 million per year to Air Force aircraft. These consequences mandate a thorough understanding of urban roost situations and timely roost man-agreement where the potential for human health and safety problems exists.

On the beneficial side, starlings eat large quantities of insects and other invertebrates, especially during spring. Many of these invertebrates, such as lawn grubs, are considered to be pests. This benefit, however, is partially off-set by the fact that starlings often take over nest cavities of native insect-eating birds. As trends move toward lower pesticide use and sustainable, low-input turf and agricultural systems, the role of starlings and other birds may become more important. Research is needed to further under-stand potential positive impacts of starlings and to learn how to maximize potential benefits while minimizing problems.

Although starlings are frequently associated with damage problems, some of which clearly cause substantial economic losses, the economics of damage in relation to the cost and effectiveness of controls are not well understood. Several factors contribute to this: (1) Starlings are difficult to monitor because they often move long distances daily from roost to feeding areas, and many migrate. (2) Effectiveness of controls, particularly in relation to the total population in an area, is difficult to document. For example, does population reduction in a particular situation reduce the problem or merely allow an influx of starlings from other areas, and how does this vary seasonally or annually? In addition, does lethal control just substitute for natural mortality or is it additive?

(3) The economics of interactions with other species are difficult to measure. For example, how much is a bluebird or flicker worth, and what net benefits occur when starling interference with native cavity-nesting birds is considered? (4) Other factors such as weather and variation among problem situations complicate accurate evaluation of damage and the overall or long-term effectiveness of controls. These points, as well as others mentioned in this chapter, are examples of factors that must be considered in assessing the total economic impact of starlings. Clearly, to minimize starling-human conflicts we need a better understanding of starlings and their interactions with various habitats and control measures.

Legal Status

European starlings are not protected by federal law and in most cases not by state law. Laws vary among states, however, so check with state wildlife officials before beginning a control program. In addition, state or local laws may regulate or prohibit certain control techniques such as shooting or the use of toxicants.