Michael R. Conover

Stimuli Eliciting Distress Calls in Adult Passerines and Response of Predators and Birds to Their Broadcast

This study examined the response of birds and captive predators to the broadcast of distress calls and the effect of different stimuli on the elicitation ofthese calls. In doing so, this study tested two hypotheses about why adult passerines should distress call when physically constrained: the calls are designed 1) to attract attention, or 2) to startle the predator into releasing the caller. Birds often responded to both interspecific and intraspecific distress calls by approaching the sound source, but they rarely mobbed or engaged in any behavior that would aid the caller in escaping. The playback of a distress call had little effect on most captive opossums (Didelphis marsupialis) and raccoons (Procyon lotor) which were attacking a caged starling (Slurnus vulgaris). However, distress calls startled one opossum and two raccoons and provoked two other raccoons into a more severe attack. Birds only distress called when physically constrained. All passerine species that were tested, except brown-headed cowbirds (Molothrus ater), emitted distress calls, but in no species did every individual call. Distress calls usually were of short duration, interrupted by periods of silence, and paired with struggling behavior. Birds were more likely to distress call when held by the limbs rather than the body or neck, when moved, or when viewing a rapidly approaching object. These results indicate that one function of distress calls for most passerines is to startle the predator, but that other functions also are likely. My results also support the hypothesis that birds approach a distress caller to acquire information about the predator that has captured the caller.

Herbivory by Canada Geese: Diet Selection and Effect on Lawns.

Flocks of free-ranging Canada Geese (Branta canadensis) often are considered nuisances when they graze on lawns because they litter the sites with fecal material, and their grazing often is perceived to be detrimental to the turf. I tested whether goose grazing had changed the composition of grass species at 20 sites in Connecticut where geese were considered nuisances. At these sites Kentucky bluegrass (Poa pratensis) was less prevalent in areas grazed heavily by geese than in areas of the same lawn that received light grazing. At six sites where up to several hundred geese wait daily for food handouts, 46% of the ground was devoid of vegetation except for a moss. I examined the palatability of different grass species to Canada Geese by giving captive birds the opportunity to feed in plots of five cool-season turf-grass species. The birds spent more time feeding in plots of Kentucky bluegrass and less time feeding in plots of tall fescue (Festuca Araneidae cv. K-31) that would have been expected if the geese were grazing among plots at random. Time spent grazing in plots of colonial bent grass (Agrostis tenuis cv. Highland), perennial ryegrass (Lolium peatland), and red fescue (F. rubra) did not differ from the expected. Feeding preferences for grass species were negatively correlated with the ash content of the leaves and with the amount of force required to sever a specific leaf mass. Captive Canada Geese would not feed on common periwinkle (Inca minor), Japanese pachydermum (pachydermum terminals), or English ivy (headnotes helix). These results suggest that Canada Goose numbers can be reduced at sites where they are foraging on turf if lawns are replaced by an unpalatable ground cover, or, to a lesser extent, with a tough-leaf grass species such as tall fescue.

Characteristics of Ungulate Behavior and Mortality Associated with Wire Fences

Abstract We studied the characteristics of pronghorn (Antilocapra americana), mule deer (Odocoileus hemionus), and elk (Cervus elaphus) mortalities associated with wire fences along roads in Colorado and Utah, USA, from June 2004 to June 2005. We estimated an average annual mortality occurrence of 0.25 mortalities/km for the wire fences studied (0.08 mule deer mortalities/km, 0.11 pronghorn mortalities/km, and 0.06 elk mortalities/km) or 0.5 mortalities/km of road. The highest wire fence–mortality rates in our study area occurred during August, which coincided with weaning of fawns. Mule deer and pronghorn jumped fences in >81% of observed crossings. Mortalities were largely caused by animals getting caught between the top 2 wires. Mule deer experienced higher fence-mortality rates than elk or pronghorn because they crossed fences more frequently (P < 0.001) and spent more time in road right-of-ways (P < 0.001) than the other species. Juveniles were 8 times more likely to die in fences than adults. Woven-wire fences topped with a single strand of barbed wire were more lethal to ungulates than woven wire with 2 strands of barbed wire above it or 4-strand barbed-wire fences (P < 0.01). There was a direct relationship between the frequency of fence mortalities and ungulate abundance (r2 = 0.83). Traffic volumes were inversely related to fence-mortality frequencies (r2 = 0.50) and ungulate densities along the right-of-way (r2 = 0.50).

EFFECT OF PREVENTIVE COYOTE HUNTING ON SHEEP LOSSES TO COYOTE PREDATION

Aerial hunting is commonly used by agriculture agencies in the Intermountain \Vest to reduce coyote (Canis latrans) predation on domestic sheep. \Ve assessed the effect of aerial hunting of coyotes on sheep losses to coyotes, and the need for corrective pedation management (hours of work, device nights) on the same pastures when sheep arrived for the subsequent summer grazing season (3-6 months after aerial hunting). Comparisons were made between paired pastures with (treated) and without (untreated) winter aerial hunting from helicopters. Average (I t SE) pasture size was 45.2 t 14.1 km2 (n = 21) for treated pastures and 30.9 t 4.6 km2 (n = 21) for untreated pastures. There was an average of 1,098 t 88 ewes and 1,226 2 149 lambs in treated pastures, and 1,002 t- 149 ewes and 1,236 t 79 lambs in untreated pastures. The number of dead lambs located and confirmed killed by coyotes (confirmed hlls) was less in treated pastures (2.7 t 0.6) than in untreated pastures (7.3 i 1.6; P = 0.01). To estimate total lamb losses to coyotes, we multiplied the proportion of knowvn lamb deaths that were confirmed coyote kills by the number of missing lambs and added the resulting figure to the number of confirmed kills. These estimates of lamb loss to coyotes were also lower in treated (11.8 t 6.2) than untreated pastures (35.2 t 8.1; P = 0.02). Hours required for summer coyote control also were less (P = 0.01) in treated pastures (37.3 t 8.5) than in untreated pastures (57.2 t 11.3). Winter aerial hunting increased the mean number of coyotes killed annually per pasture from 2.0 t 1.0 to 5.7 t 1.1 (P = 0.04), but it did not affect the number of coyotes removed during summer coyote control (P = 0.52). Based on 1995 values for Utah lambs and labor, winter aerial hunting of coyotes had a benefitcost ratio of 2.1:l. JOURNAL OF WILDLIFE MANAGEMENT 63(2):606-612

Response of birds to different types of food repellents

Birds varied in their response to food treated with a taste repellent (copper oxalate) or either of two aversive conditioners, (lithium chloride and methiocarb). All repellents reduced the amount of treated food consumed by captive birds having easy access to unlimited alternate food supplies, although copper oxalate was ineffective against free-ranging birds. Once copper oxalate and methiocarb were removed from food, food consumption returned to normal. Birds, however, continued to avoid foods previously treated with LiCl that was disguised by micro-encapsulation or adding it to previously salted food. These results indicate that birds avert from the taste or sight of the repellent when it is detectable and avert from the food when the repellent is undetectable. Hence, non-detectable aversive conditioners have a greater potential to protect untreated food sources.

Feeding preferences and changes in mass of Canada Geese grazing endophyte-infected tall fescue

In the late 1940s and 1950s southern farmers began planting a newly-discovered tall fescue cultivar (Kentucky-3 1), which was much hardier and more productive than other cultivars. Unknown at the time, this cultivar was infected with the endophytic fungus Acremonium coenophialum. By the 1910s there were over 14 million ha of tall fescue pastures in the U.S., mostly in the southern and south-central states, and most were infected with the fungus (Shelbv and Dalrvmule 1987. Stuedemann and Ho>eland 1988). The total infected area may have increased recently, because tall fescue has been the predominant grass seeded in Conservation Reserve Program plantings in the central and southern

EXPERIMENTAL-EVIDENCE THAT FEMALE-FEMALE PAIRS IN GULLS RESULT FROM A SHORTAGE OF BREEDING MALES

The Condor 8 6:472~ 76

Biases in bird strike statistics based on pilot reports

Collisions between birds and aircraft are a concern because they threaten human safety and result in costly repairs. Most data on bird strikes have been provided by pilots and may be incomplete or biased. To assess whether bird strike statistics derived from pilot reports are biased, we compared the number of pilot-reported bird strikes at a Hawaiian airport during 1990-94 to the number of bird strikes obtained from regular runway searches for dead birds. We documented 526 bird strikes, of which only 25% were reported by pilots. Pilot reporting rates (percentage of all strikes reported by pilots) varied by species involved, number of birds struck, season, time of day, location on the runway during the landing phase, and the birds mass. Reporting rates were not, however, correlated to size of the bird. Pilot reporting rates were independent of wind speed, wind direction, and percent cloud cover, and reporting rates were similar during landings and takeoffs. We found that bird strike statistics derived from pilot reports were biased. A sole reliance on such data can lead to incorrect conclusions and may cause airports to select inappropriate measures and times to reduce bird strikes.

Analysis of bird strikes at a tropical airport

Bird-aircraft collisions (bird strikes) are a major problem worldwide because they threaten passenger safety and result in costly repairs and lost revenue for the commercial air carrier. From 1990 to 1994, we conducted runway sweeps at Lihue Airport on Kauai, Hawaii searching for avian remains from bird-aircraft collisions. Three species of granivorous birds, 2 owl species, and the Pacific golden-plover (Pluvialis julva) composed >80% of the bird strikes. Ninety-one percent of the strikes involved solitary birds; 9% involved >1 bird. Bird strikes were positively correlated with mean monthly rainfall, perhaps due to increased seed production along runways during the rainy months, resulting in increased bird use in hazardous areas. Bird strike rates were also higher when winds were from a southwesterly direction and lower when cloud cover was 100%. Larger, faster commercial air carriers exhibited higher strike rates than military or general aviation types, with engine ingestions being most common, followed by strikes on the windshield and nose. Ingestions resulted in losses >

Concentrations of selenium and mercury in eared grebes (Podiceps nigricollis) from Utah's great Salt Lake, USA

1.5 million in damage. Damage was caused by species ranging in mass from 13-1,300 g. More bird strikes occurred during landings than takeoffs with strikes unevenly distributed along the runway. During the landing phase, more bird strikes than expected occurred at the point of touchdown, whereas most strikes occurred in the mid-portion of the runway during takeoffs.