Michael W. Collopy

Bat activity in thinned, unthinned, and old-growth forests in Western Oregon

Many aspects of the influences of forest management activities on bats (Chiroptera) in the Pacific Northwest are poorly known, We compared thinned and unthinned forest stands of the same age and old-growth forest stands to determine potential differences in structure and amount of use by bats. We hypothesized that activity levels of bats would differ in stands differing in structure as a result of management bistory and that activity of bats would be similar in stands of similar structure. We used automated ultrasonic detectors (Anabat II) to record calls of bats in 50-100-year-old thinned and unthinned stands, and in old-growth (200 yr old) stands in the Oregon Coast Range during the summers of 1994 and 1995. Our median index of bat activity was higher in old-growth than in unthinned stands and higher in thinned than in unthinned stands, We were not able to detect a significant difference between the index of median bat activity for old-growth and thinned stands. More than 90% of identifiable passes were identified as calls from Myotis species. The 3 stand types we examined differed in certain structural characteristics such as density and size of trees, and amount of overstory and understory cover. We concluded that the structural changes caused by thinning may benefit bats by creating habitat structure in young stands that bats are able to use more effectively.

The Role of Predation in Determining Reproductive Success of Colonially Nesting Wading Birds in the Florida Everglades

In a sample of 1,609 marked nests of five species of Ciconiiformes in 21 colonial nesting aggregations in the Everglades, evidence of abandonment without destruction of nest contents accounted for 31.3% of failures. In 66.9% of the failures, evidence at the nest suggested either predation resulting in nest failure or postabandonment scavenging of nest contents. In a sample of 106 nests isolated by a nonrepelling tracking medium, we found predation by snakes to account for 23% of nest failures; mammals accounted for an additional 20%. Failures due to these two categories accounted for 12% of the treated nests; abandonments may have been considerably underrepresented in this sample of nests. Mammalian predators rarely visited widely distributed baited tracking stations in the marsh, and we hypothesize that even 5-10 cm of water can substantially restrict travel by raccoons, foxes, and rats. Visitation by mammals to colonies occurred only when the water surrounding them receded, and was not related to the presence of alligators or distance from permanently dry land. We found little evidence of avian predation on wading bird nests, though birds readily scavenged abandoned nest contents. We discuss several attributes of the Everglades marshes which may limit access of predators to nesting colonies.

Effectiveness of Avian Predator Perch Deterrents on Electric Transmission Lines

Abstract A new high-voltage transmission line in north-central Nevada, USA, was considered a potential threat to greater sage-grouse (Centrocercus urophasianus) because avian predators are attracted to and hunt from elevated perches. As a mitigation measure, perch deterrents were installed on the transmission line towers at the time of construction; in addition, 2 existing high-voltage transmission lines were retrofitted with deterrents. Previous published studies have investigated the efficacy of perch deterrents in preventing or reducing electrocution of avian predators and fecal contamination of insulators, but none have evaluated deterrents as a means of eradicating perching on towers. We conducted point transect surveys and perching-duration observations of corvids and raptors and determined that although perch deterrents did not prevent perching, the perching duration of raptors on the deterrents was reduced compared to other perching substrates. Perching of raptors indicated that some hunting most likely took place from the towers; therefore, the deterrents did not completely obviate the threat that avian predators posed to greater sage-grouse. Although the deterrents reduced the probability of avian predators perching on the towers, avian predators overcame the deterrents to take advantage of the height of the towers where no other perches of similar height existed. The perch deterrents as designed did not have the desired short-term effect on avian predators, but further monitoring may reveal longer-term effects and distinguish perching behaviors specific to different species of avian predators.

Survival Probability and Mortality of Migratory Juvenile Golden Eagles from Interior Alaska

Abstract The conservation of golden eagles (Aquila chrysaetos) requires a thorough understanding of their demographic parameters. Productivity, commonly measured as the number of nestlings or fledglings per pair, is the parameter reported by most studies of nesting golden eagles and is often used as a measure of their population status. Survival may be an equally or more important parameter to measure; however, survival rates of golden eagles are not well documented. We used satellite telemetry to estimate the probability of first-year survival for migratory golden eagles raised in Denali National Park and Preserve, Alaska, USA. We calculated the probability of first-year survival using program MARK. Based on the best approximating model, monthly survival probability was 0.88 ± 0.04 (mean ± SE) during the autumn migration and early winter period for golden eagles marked in 1997 and 0.78 ± 0.05 during the same period for golden eagles marked in 1999. Monthly survival during the remaining 3 periods (i.e., late winter, spring migration, summer) was 0.94 ± 0.03 for both cohorts. Survival during the entire 11-month period was 0.34 ± 0.10 for the 1997 cohort and 0.19 ± 0.07 for the 1999 cohort. Causes of mortality included starvation, electrocution, and poaching. Our results indicate that low first-year survival may limit recruitment and we recommend that golden eagle monitoring programs include survival estimates.

Movements of Golden Eagles (Aquila chrysaetos) from Interior Alaska During Their First Year of Independence

Abstract We used satellite telemetry to study year-round movements of two cohorts of juvenile Golden Eagles (Aquila chrysaetos) from Denali National Park and Preserve, Alaska. Radiotagged Golden Eagles started autumn migration between 15 September and 5 October and arrived on their winter areas 31 to 86 days later. Cumulative tracking distances during autumn migration ranged from 818 to 4,815 km. Peak tracking velocities during autumn migration reached 261 km day−1 in 1997 and 472 km day−1 in 1999. Golden Eagles wintered from southern Yukon Territory to southern New Mexico, and most spent the winter within 75 km of the location where they terminated their autumn migration. Spring migration occurred from late March through mid-June. Eagles showed little fidelity to their autumn migration paths as they migrated northwest in spring through western Canada and into Alaska. Duration of spring migration ranged from 24 to 54 days, and cumulative tracking distance during spring migration ranged from 2,032 to 4,491 km. Peak tracking velocities during spring migration reached 284 km day−1 in 1998 and 330 km day−1 in 2000. In contrast to juvenile Golden Eagles raised at temperate latitudes in North America, juveniles raised in Denali traveled thousands of kilometers across western North American during their first year of independence. Our results suggest that conservation strategies for migratory Golden Eagles from Denali, and perhaps from other areas in northern North America, require a continental approach. Movimientos de Individuos de Aquila chrysaetos desde el Interior de Alaska durante su Primer Año de Independencia

Food Caching by Female American Kestrels in Winter

Prey caching is documented for many birds of prey. A review of some raptor species which cache food was provided by Mueller (1974). Additional records of caching among falconiforms were reported by Roest (1957), Gullion (1965) and Balgooyen (1976). Prey caching has also been noted in many owl species (Allen 1924, Lockley 1938, Wallace 1948, Mossman 1955, Jansson 1964, Norburg 1964, Grant 1965, Ligon 1968, Catling 1972). For the purposes of this study, I designated caching behavior as any activity involved in storing or retrieving prey. Storage is that aspect of caching in which a food item is placed in a cache. Retrieval is that aspect of caching in which a stored food item is removed from a cache. Typical prey retrieving behavior which failed to produce a food item is called here an attempt to retrieve. Most accounts of caching by American Kestrels (Falco sparverius) are based on relatively few observations of wild or captive birds (Pierce 1937, Tordoff 1955, Roest 1957). Stendell and Waian (1968) observed a female kestrel store 17 prey items in one cache over a 40-day period. Balgooyen (1976) watched kestrels caching food during the breeding season. He discussed the advantages of caching food, especially during periods when inclement weather is common and

Researcher Disturbance in Colonies of Wading Birds: Effects of Frequency of Visit and Egg-Marking on Reproductive Parameters

-In two closely matched colonies of Tricolored Herons (Egretta tricolor) we found no differences in reproductive parameters of the one visited frequently (16 times) and the other visited infrequently (7 times). Visits to colonies were standardized and were initiated only after most of the herons had partially completed their clutches. These results suggest that limited colony visitations beginning after courtship and early egg-lalying do not result in large disturbance effects. We caution, however, that these findings should not be applied without further testing, especially since the colonies we studied were relatively free of aerial and ground predators. We also found that letters marked on the sides of eggs were turned down by parental birds significantly more often than expected due to chance. We suggest researchers label eggs inconspicuously on the ends or not at all. Received 13 December 1988, accepted 29 June 1989.

Effects of Egg Removal on Bald Eagle Productivity in Northern Florida

We removed eggs from bald eagle (Haliaeetus leucocephalus) nests in northern Florida from 1985 through 1988 to determine if pairs would lay again and to evaluate how egg removal affected subsequent productivity. Of 58 pairs that had first clutches removed, 45 (78%) laid a second clutch within an average of 29.4 days. In 1 study area, productivity of pairs that had their first clutch removed (1.00 young fledged/ breeding attempt) was less (P = 0.02) than control pairs (1.47) that produced their clutches during the same time period. In contrast, no difference (P = 0.75) in productivity occurred between donor (1.17) and control pairs (1.09) produced during the same period in a second study area

Postfledging nest dependence period for bald eagles in Florida

We studied the postfledging dependency period in bald eagles (Haliaeetus leucocephalus), a little studied but important period in the life cycle of avian species. Bald eagles in Florida had a postfledging dependency period of 4-11 weeks (15-22 weeks old). The length of the dependency period did not vary by year of study, sex, number of fledgings, timing of fledging, or hatch order (P > 0.05). Mean distance fledglings ranged from the nest increased with age, but they were observed in the nest or nest tree throughout the postfledging dependency period. Distance from the nest did not vary by sex, number of fledglings, or timing of fledging (P > 0.05). Over 80% of the fledgling observations were within 229 m of the nest. The boundary of the primary protection zone specified in the bald eagle habitat management guidelines for the southeastern United States is 229 m. Restrictions on human disturbance around nest sites should remain in place during the postfledging dependency period because of the close association of fledglings with the nest site. Restrictions also should be flexible because of the varying length of the dependency period.

POSTFLEDGING DEPENDENCE PERIOD OF MIGRATORY GOLDEN EAGLES (AQUILA CHRYSAETOS) IN DENALI NATIONAL PARK AND PRESERVE, ALASKA

Abstract The postfledging dependence period is not well documented for many species of raptors, including Golden Eagles (Aquila chrysaetos). From 1997 to 1999, we used satellite telemetry to estimate the length of the postfledging dependence period, and the finite survival rate of fledglings during that period, for migratory Golden Eagles in Denali National Park and Preserve, Alaska. Length of the postfledging dependence period averaged 50.1 days and ranged from 39 to 63 days. The post- fledging dependence period was longer for Golden Eagles that hatched earlier, but hatching date did not influence the date they departed their natal area. Average date of departure from the natal area was 25 September. The departure period spanned a 17-day period from 15 September to 5 October, and coincided with a series of environmental changes including decreases in day length, temperature, and prey diversity. Probability of survival during the postfledging dependence period was 0.98 (95% CI = 0.94 to 1.00). Período de Dependencia Posterior al Emplumamiento de Aquila chrysaetos en el Parque Nacional y Reserva Denali, Alaska