Eric A. Tillman

Evaluation of Bird Shield as a blackbird repellent in ripening rice and sunflower fields

Abstract Chemical repellents sometimes can provide a nonlethal alternative for reducing wildlife impacts to agricultural production. In late summer and autumn 2002, we evaluated Bird Shield™ (active ingredient: methyl anthranilate, Bird Shield Repellent Corporation, Spokane, Wash.) as a blackbird (Icteridae) repellent in Missouri rice fields and North Dakota sunflower fields. We selected 5 pairs of ripening rice fields in southeastern Missouri and randomly allocated treatments (treated and control) within pairs. The repellent was aerially applied by fixed-winged aircraft at the recommended label rate and volume (1.17 L Bird Shield/ha and 46.7 L/ha, respectively); 1 field received 2X the label rate. We observed no difference in average bird activity (birds/minute) between treated and control fields over the 3-day post-treatment period (P = 0.503). We used reversed-phase liquid chromatography to quantify methyl anthranilate residues in treated fields. The maximum concentration of methyl anthranilate in rice samples was 4.71 µg/g. This concentration was below reported threshold values that irritate birds. In North Dakota we selected 6 pairs of sunflower fields used by foraging blackbirds. We randomly selected 1 field from each pair for 2 aerial applications of Bird Shield at the label-recommended rate ∼1 week apart. The remaining 6 fields served as controls. Daily bird counts, starting the first day of application and continuing for 5–7 days after the second application, showed similar numbers of blackbirds within treated and control fields (P = 0.964). We observed no difference in sunflower damage within treated and control fields (P = 0.172) prior and subsequent to the treatment. Bird Shield was not effective for repelling blackbirds from ripening rice and sunflower fields.

Diazacon Inhibits Reproduction in Invasive Monk Parakeet Populations

Abstract Throughout the United States, managers lack safe, effective methods to control expanding populations of the invasive monk parakeet (Myiopsitta monachus). Because the reproductive inhibitor diazacon (20,25 diazacholesterol) has been used effectively in captive monk parakeets, we provided diazacon-treated sunflower seeds to birds at electric utility substations inhabited by parakeets in south Florida, USA. Nest productivity (nestlings plus eggs with embryos) averaged 1.31 (SE = 0.45, n = 100 nests) at 6 treated sites compared to 4.15 (SE = 0.68, n = 50 nests) at 4 untreated sites, a 68.4% reduction. Exposure of native bird species to treated bait was infrequent. Diazacon is an effective means to reduce reproductive success of monk parakeets, and development of methods to limit exposure of nontarget birds will enable more widespread use of this useful population management technique.

Vulture Flight Behavior and Implications for Aircraft Safety

ABSTRACT Growing vulture populations represent increasing hazards to civil and military aircraft. To assess vulture flight behavior and activity patterns at the Marine Corps Air Station in Beaufort, South Carolina, we equipped 11 black vultures (Coragyps atratus) and 11 turkey vultures (Cathartes aura) with solar-powered Global Positioning System (GPS) satellite transmitters during a 2-year study (1 Oct 2006–30 Sep 2008). Turkey vultures had larger seasonal home ranges than did black vultures, and 2 turkey vultures made round-trips to Florida. Black vultures consistently spent less time in flight (8.4%) than did turkey vultures (18.9%), and black vultures flew at higher altitudes than did turkey vultures in all seasons except summer when altitudinal distributions (above ground level) did not differ. Although we recorded maximum altitudes of 1,578 m for black vultures and 1,378 for turkey vultures, most flights were low altitude. A matrix of vulture flight altitude versus time of day revealed that >60% of vulture flight activity occurred from 4 hr to 9 hr after sunrise at altitudes below 200 m. Continuation of aggressive harassment coupled with flexible training schedules to avoid times and altitudes of high vulture activity will decrease hazards to aircraft posed by these birds.

Use of DiazaCon™ as a reproductive inhibitor for monk parakeets (Myiopsitta monachus)

Feral monk parakeet (Myiopsitta monachus) populations have become established in the United States and other countries around the world, and can cause damage to electrical facilities. Because the monk parakeet is a highly visible species and there is often public opposition to lethal control measures, non-lethal methods, such as contraception, are being developed to help control the spread of feral populations. Two gavage studies and one ad libitum nesting study were conducted to assess the efficacy of DiazaCon™ as a potential contraceptive for the monk parakeet. The first gavage study compared daily dose levels of 0, 50, 75, and 100 mg DiazaCon™ (kg bodyweight) -1 administered for 10 consecu- tive days. Cholesterol concentrations decreased significantly concomitant with a significant increase in desmosterol concentrations in the treated groups, but did not vary between sexes. Cholesterol and desmosterol concentrations did not differ significantly among DiazaCon™ groups, and cholesterol remained significantly suppressed 12 weeks after treat- ment. On the basis of these results, the second gavage study compared 5 or 10 consecutive days of DiazaCon™ adminis- tration at 50 mg kg -1 bird -1 day -1 . Cholesterol concentrations decreased significantly concomitant with a significant increase in desmosterol concentrations in the treated groups, but did not vary between sexes. Cholesterol and desmosterol concentrations did not differ significantly between DiazaCon™ groups, and cholesterol remained significantly suppressed 11 weeks after treatment. Parakeets in the nesting study were fed hulled sunflower seeds treated with a target dose of 50 mg DiazaCon™ kg -1 bird -1 day -1 . Birds consumed enough to receive an average dose of 34 mg kg -1 pair -1 day -1 , or 17 mg kg -1 bird -1 day -1 . Birds in the treated group laid an average of 1.6 ± 0.7 eggs per clutch compared with 3.9 ± 1.1 eggs per clutch in the untreated control group. None of the eggs laid by treated birds hatched compared with 1.1 ± 0.6 eggs per clutch hatching in the control group. Reproductive inhibition was effective for the length of the breeding season, at which time the study was stopped and no more data were collected. DiazaCon™ is a promising avian oral contraceptive that should be further investigated in a field setting with monk parakeets.

BIOLOGY OF INVASIVE MONK PARAKEETS IN SOUTH FLORIDA

Abstract Monk Parakeets (Myiopsitta monachus) have been in Florida for >40 yrs, having been imported by the thousands for the pet trade. This conspicuous, charismatic species is now widely established, but relatively little is known about its population biology outside South America. We examined 845 parakeets from 385 nests from nest removals and collections by utility company personnel in 2003/2004 and 2006/2007 to document body size and aspects of reproductive biology and primary molt. Body measurements confirm Monk Parakeets in south Florida belong to the monachus subspecies. Adult males averaged 1.5 to 3.5% larger than females, but the body mass of females exceeded that of males during March–May, the period of egg development. The breeding season in south Florida commences in late winter/early spring with fledglings first appearing in the second week of June. Nest contents (eggs plus nestlings) averaged 5.6 for multiple-entry nests compared to 4.9 for single-entry nests. Over 94% of the adults we examined were replacing primary feathers during June–August. The extent and timing of breeding and molt in south Florida are virtually identical to those in South America, although offset by ∼6 months. Monk Parakeets in south Florida retain a fixed annual cycle characteristic of the ancestral population, but their flexible behavior enables them to adapt and thrive in new environments.

Nicarbazin bait reduces reproduction by pigeons (Columba livia).

Development of effective methods for reducing populations of overabundant nuisance bird species continues to challenge wildlife biologists. Reproductive inhibition, although conceptually pleasing, has been difficult to implement because of the lack of a safe, approved avian contraceptive. Recently, however, nicarbazin received regulatory approval in the United States for use as a bait to decrease hatchability of resident Canada goose (Branta canadensis) and feral pigeon (Columba livia) eggs. In anticipation of the feral pigeon registration, we evaluated efficacy by exposing captive pairs of nesting pigeons to nicarbazin bait for 4 h daily. Egg production was unaffected, but only 9 of 22 eggs hatched, a 59% reduction from pre-treatment when each of the 11 test pairs produced 2 nestlings. In the recovery phase, when treated bait was removed, the 11 pairs produced 18 nestlings. All nestlings produced during the study appeared healthy and normal, and there was no mortality among the adult pairs. Nicarbazin is an effective and safe means of reducing hatchability of feral pigeon eggs that can be used within an integrated management plan to reduce feral pigeon populations.

Impacts from control operations on a recreationally hunted feral swine population at a large military installation in Florida

Feral swine were targeted for control at Avon Park Air Force Range in south-central Florida to avert damage to sensitive wetland habitats on the 40,000-ha base. We conducted a 5-year study to assess impacts from control to this population that had been recreationally hunted for many years. Control was initiated in early 2009. The feral swine population was monitored from 2008 to 2012 using a passive tracking index (PTI) during the dry and wet seasons and using recreational hunter take rates from the dry season. All three indices showed substantial feral swine declines after implementing control, with indices leveling for the final two study years. Military missions and recreational hunting seasons impacted temporal and spatial consistency of control application, thereby limiting further impacts of control efforts on the feral swine population. The PTI was also able to monitor coyotes, another invasive species on the base, and detect Florida black bear and Florida panther, species of particular concern.

Invasive black spiny-tailed iguanas (Ctenosaura similis) on Gasparilla Island, Florida, USA.

The native range of Ctenosaura similis extends from southern Mexico through Panama. From an initial introduction of 3 animals in 1979, the species now numbers in the thousands on Gasparilla Island in southwest Florida. In response to complaints of property damage from residents and threats to native species, local officials and the US Department of Agriculture Wildlife Services began a removal program in 2008. Through 2011, trappers removed 9467 ctenosaurs. The number removed declined from 32 iguanas/day in 2008 to 1.9 iguanas/day in 2011 despite no easing of the control effort. We necropsied 2757 ctenosaurs to document aspects of their natural history. Females outnumbered males overall, although the largest size class (>300 mm snout-vent length) included 32 males and just 2 females. Reproduction was seasonal. We found oviducal eggs in females from early Apr to early Jun, approximately 2 months later than C. similis in its native range. We trapped hatchlings from late Jul to early Oct coincident with the summer rainy season. Clutch size increased with female body size, with 62 being the largest clutch size recorded. In general, the biology of the invasive population on Gasparilla Island resembles native C. similis populations in Central America, except for the lack of large individuals. We suggest that shorter day length and colder temperatures create environmental conditions that are suboptimal for individual growth compared to those in the native range.

Crow Pellets from Winter Roosts in Lancaster, Pennsylvania

Abstract Although crows cast pellets, there is little quantitative information on pellets from Corvus brachyrhynchos (American Crow), and none from C. ossifragus (Fish Crow). During a study of crow roost dispersal in Lancaster, PA, we collected samples of pellets from several locations. By mass, pellets consisted mostly of grit and other fine inorganic material, various seeds (principally Toxicodendron radicans [Poison Ivy] and Celtis occidentalis [Common Hackberry]), and vegetation remnants. Six pellets contained small-mammal bones. Because the Lancaster winter crow population included many Fish Crows, the source of the pellets was not certain. To clarify this, we compared the size of the Lancaster crow pellets to those produced by captive Fish Crows, and we provide the first quantitative description of pellets for either species. Our size comparisons suggest that >90% of the pellets in our sample from Lancaster were produced by American Crows.