Joseph L. Guarino

Foods of the Red-Winged Blackbird in Brown County, South Dakota

An analysis of the gizzard contents of 702 red-winged blackbirds (Agelaius phoeniceus) collected from l9S9 through 1965 during the spring, summer, and early fall in northeastern South Dakota showed that a weed seed, bristle grass (Setaria spp.), occurred most frequently (68 percent of the gizzards ) and in the largest quantity ( 23 percent of the volume ) . Corn ( Zea mays ) was eaten more frequently (30 percent) and in larger amounts (11 percent) than all other cultivated grains. Oats (Avens sativa), wheat (Triticum aestivum), and millet (Panicum miliaceum) made up most of the remaining plant food consumed. Animal matter, mostly l}eetles (Coleoptera), contributed 25 percent of the total volume eaten, with the greatest incidence and volume ( 96 and 45 percent ) being recorded duling the nesting period. Grit accounted for 14 percent of the volume eaten. FOODS OF REDWINGS * Mott et a. 983 In contrast, the circular trap allowed a magpie to walk into the entrance from any point of origin on the trap, without rounding right-angle corners or other obstacles.

Decoy plantings for reducing blackbird damage to nearby commercial sunflower fields

Field tests were conducted in North Dakota in August, September and October 1981 to 1983 inclusive, to determine if decoy plantings of nine sunflower fields and one interplanted corn/sunflower field would reduce blackbird (Icterinae) damage to nearby commercial sunflower fields. Total seed consumption by blackbirds of sunflower (90 ha) and corn (7 ha) was 87860 kg, worth US

A METHOD FOR APPRAISING BLACKBIRD DAMAGE TO CORN

26533·72 based on the average 3-year market price of

Use of 4-Aminopyridine to Protect Ripening Corn from Blackbirds

0·302/kg. The average cost of planting a decoy field was

Fertility of Eggs Produced on Territories of Vasectomized Red-Winged Blackbirds

74/ha for a total cost of

Reducing Bird Damage to Ripening Cherries with Methiocarb

7178. The yearly cost-benefit ratio varied from 1:2 · 1 to 1:4·7 with an overall study average of 1:3·7. From 1981 to 1983, the annual median seed consumption in decoy fields was 917, 1210, and 1121 kg/ha compared with surrounding commercial fields within 11 km of the decoy fields which had losses of 4,99 and 115 kg/ha, respectively. In 1981, a comparison of losses between sunflower fields in Bottineau County and commercial sunflower fields within 11 km of decoy fields provided statistical evidence (P =0·0651) that there was less damage to commercial fields surrounding the decoy crops; this difference in losses was attributed to the presence of the decoy fields. Average blackbird numbers observed entering decoy fields per minute per hectare were 69 (1981), 49 (1982) and 91 (1983). Peak roost populations associated with decoy fields ranged from 72000 to 215000 blackbirds. Overall, redwings constituted about 83% of all blackbirds observed in decoy fields.

Costs of Wintering Starlings and Red-Winged Blackbirds at Feedlots

The appraisal method described was developed from 19161 to 1965 at the Sand Lake Na- tional Wildlife Refuge, South Dakota. In 1962, 600 undamaged corn ears were collected at random dried, and sorted by half-inch lengths into 15 size classes, and the kernels of each half-inch section were shelled off and weighed. The average cumulative weight of the kernels on each half-inch section for each size class was listed in a table that allowed an estimate of the dry weight lost to be read off from the length of the ear and the length of the damaged section. After adjustment by a standard percentage (by which any 1 years crop was heavier or lighter than the 1982 crop), the data showed a uniform relationship between length and weight. Regression equations derived for each size class (Rq at least 0.90 in all but one case) permitted a more accurate table to be generated mathematically. Total weight of corn lost to blackbirds each year was estimated by sampling two plots ( each a 100-ft section of a corn row) per field on about 15 percent of the fields in the 94-square-mile study area. Damage on each plot was measured after the bird damage season simply by counting the number of damaged and undamaged ears and measuring the length of the damaged ears and the length of dam- age they had sustained. The chief advantage of this appraisal is the small amount of time it requires. Plots are examined only once, only damaged ears are measured, and damage is recorded directly from the length-weight table as weight of marketable corn lost per ear.

Protecting Ripening Corn from Blackbirds by Broadcasting 4-Aminopyridine Baits

A toxic, fright-producing chemical, 4-aminopyridine, was tested for alleviating damage by redwinged blackbirds (Agelaius phoeniceus) to ripening corn in Brown County, South Dakota. The treatment reduced losses by about 7() percent in 8 contiguous sections colntaining 1,013 acres of corn. Numbers of blackbirds using the treated area fell sharply during a 5-day period after treatment began and remained at a low level for the remainder of the damage season. The technique was highly specific for blackbirds. Although pheasants (Phasianus colchicus) were abundant, there was no evidence that any were affected, and mortality among other species of birds was negligible. Blackbirds, principally red-winged blac3<birds, damage ripening corn in many areas of the United States and create a need for an effective, safe, and economical means of controlling damage. Many techniques have been tried, some providing a degree of relief ( Neff 194S, Neff and Meanley 1957, Bird and Smith 1963), but, for the effort expended, most have failed to give the protection desired. Since 1, the Denver Wildlife Research Center has investigated methods of controlling blackbird damage to ripening field corn at Sand Lake National Wildlife Refuge, South Dakota ( De Grazio 1964 ) . From 1961 to 1963, we detennined that redwings destroyed an average of about 3 bushels of com per acre in a 94-section survey area surrounding the marshes of this refuge. In 1962 and 1963 experiments, we sprayed partially husked ears of standing corn with a chemical frightening agent, 4-aminopyridine. Some species of birds affected with 4aminopyridine emit distress cries and perform aerial distress displays, and a few affected individuals often frighten the other 1 Deceased. birds in the floek and cause thenr to leave. Although this chemieal was first synthesized by Koenigs and Gredner ( 1931), its unique aetion on birds was discovered by Goodhue et al. (l964), and its utility for controlling damage by birds in some situations was demonstrated by Goodhue and Baumgartner (1965s, b). In redwings, we found that a lethal dose of 4-aminopyridine was necessary to produee distress behavior. The acute oral LD50, as well as the dose necessary tol produce distress in 50 percent of the birds, was 2.4 mg/kg (95 pereent eonfidence limits, 1.5-3.8 mg/kg). At this level, distress usually began about 15 minutes after dosing and lasted for about 20 to 30 minutes. Our studies in 1963 indieated the eonditions for using 4-aminopyridine sprays effectively, the number of treatments necessary to provide proteetion during the damage season, and the number of treated ears required per aere. These investigations showed that the feedingl habits of blackbirds could be disrupted after they had beeome established in a field, and that a field could be protected even though only a few birds were affeeted. Often, a few