Teryl G. Grubb

Effects of helicopter noise on Mexican spotted owls

Military helicopter training over the Lincoln National Forest (LNF) in southcentral New Mexico has been severely limited to protect nesting Mexican spotted owls (Strix occidentalis lucida). To evaluate nesting and nonnesting spotted owl responses to helicopter noise, we measured flush frequency, flush distance, alert behavior, response duration, prey delivery rates, female trips from the nest, and nest attentiveness during manipulated and nonmanipulated periods, 1995-96. Chain saws were included in our manipulations to increase experimental options and to facilitate comparative results. We analyzed stimulus events by measuring noise levels as unweighted one-third-octave band levels, applying frequency weighting to the resultant spectra, and calculating the sound exposure level for total sound energy (SEL) and the 0.5-sec equivalent maximum energy level (LEQ max 0.5-sec) for helicopters, and the 10-sec equivalent average energy level (LEQ avg. 10-se) for chain saws. An owl-weighting (dBO) curve was estimated to emphasize the middle frequency range where strigiform owls have the highest hearing sensitivity. Manipulated and nonmanipulated nest sites did not differ in repro- ductive success (P = 0.59) or the number of young fledged (P = 0.12). As stimulus distance decreased, spotted owl flush frequency increased, regardless of stimulus type or season. We recorded no spotted owl flushes when noise stimuli were >105 m away. Spotted owls returned to predisturbance behavior within 10-15 min after a stimulus event. All adult flushes during the nesting season occurred after juveniles had left the nest. Spotted owl flush rates in response to helicopters did not differ between nonnesting (13.3%) and nesting seasons (13.6%; P = 0.34). Spotted owls did not flush when the SEL noise level for helicopters was <102 dBO (92 dBA) and the LEQ level for chain saws was -59 dBO (46 dBA). Chain saws were more disturbing to spotted owls than helicopter flights at comparable distances. Our data indicate a 105-m buffer zone for helicopter overflights on the LNF would minimize spotted owl flush response and any potential effects on nesting activity.

Assessing human disturbance of breeding bald eagles with classification tree models

We recorded 4,188 events of human activity and associated bald eagle (Haliaeetus leucocephalus) response in the vicinity of 13 central Arizona nest sites during 1983-85. A hierarchical classification of 9 dependent and 3 independent parameters was developed to quantify pedestrian, aquatic, vehicle, noise (gunshot/sonic boom), and aircraft disturbance groups. Type and frequency of response varied inversely with the distance from an eagle to the disturbance. Bald eagles were more often flushed from perches than nests and were most easily disturbed when foraging. Pedestrian was the most disturbing human activity, whereas aircraft was the least. We developed classification tree (CART) models for pooled and group disturbances to evaluate response severity and to formulate disturbance-specific management criteria. Response frequencies and critical distances for pooled disturbance were 64% at 583 m. Frequencies, distances, and the influence of secondary characteristics varied among disturbance groups. The CART models ranked distance to disturbance as the most important classifier of eagle response, followed in decreasing order of discriminatory value by duration of disturbance, visibility, number of units per event, position relative to affected eagle, and sound. This procedure offers improved specificity in human disturbance assessment. J. WILDL. MANAGE. 55(3):500-511 The variable effects of human activity on the reproductive performance of bald eagles (Grier 1969, Fraser 1985) imply a threshold for detrimental impact between pristine isolation and outright destruction. Because that threshold can be highly variable and often subtle, its determination is difficult and requires controlled experimentation (Grier and Fyfe 1987). Yet, experimental disturbance research on bald eagles is limited, with major emphasis on flushing distances and frequencies (Stalmaster and Newman 1978, Knight and Knight 1984, Fraser et al. 1985). Distance has been the primary mechanism of protection in traditional breeding bald eagle management, with distance guidelines typically applied unilaterally to all disturbance types. Management concepts to protect nesting bald eagles have evolved from concentric-circle buffer zones at nest sites (Mathisen 1968), through single territory zonation (Mathisen et al. 1977, U.S. Fish Wildl. Serv. 1981), to a multiple territory, regional approach (e.g., F. B. Isaacs and G. Silovsky, Bald Eagle Manage. on the Fremont Natl. For., U.S. For. Serv., Lakeview, Oreg., 1981). These distance-oriented zonation approaches also have included temporal control and audio/visual buffering guidelines. Because of the complex, multivariate nature of disturbance thresholds, site-specific management guidelines have been consistently recommended. Various aspects of disturbance (i.e., distance, noise, timing, position, visibility) have been mentioned or specifically addressed in previous bald eagle research (Grubb 1980, Hansen et al. 1980, Andrew and Mosher 1982). Knight and Knight (1984) postulated that flight distances licited by different types of disturbances during different bald eagle behaviors could be used to develop zones for restricting human activities. However, simultaneous identification and analysis of an inclusive range of dependent and independent factors inherent in disturbance management are lacking. We present a hierarchical scheme for evaluating potentially disturbing human activity. With data collected following that scheme, we develop disturbance-specific, quantitative models for predicting bald eagle response frequencies and for formulating management criteria. Although we do not present a disturbance threshold for detrimental impacts on reproductive performance, we intend these techniques to be a step toward that goal by being more specific in assessing disturbance. We thank the 71 Forest Service volunteers and the many professional personnel of the Tonto, Prescott, and Coconino national forests whose dedication and field assistance during 1983-85

HABITAT ASSOCIATIONS OF SYMPATRIC RED-TAILED HAWKS AND NORTHERN GOSHAWKS ON THE KAIBAB PLATEAU

Abstract We investigated habitat association of sympatric red-tailed hawks (Buteo jamaicensis) and northern goshawks (Accipiter gentilis) at 2 spatial scales centered on nest sites: (1) fine-scale patterns of forest structure and topography within 16-m radius circles (0.08 ha), and (2) midscale patterns of forested and nonforested areas, forest fragmentation, and topography within 2,085-m-radius circles (1,367 ha). Nonforested areas were defined as any area lacking >20% canopy closure within a 30 × 30-m cell. At both scales, red-tailed hawk associations were more variable and goshawk associations less variable. At the fine scale, goshawks were consistently associated with open understories, tall trees, and gentle slopes (x̄ = 9.6°, SD = 6.9) while red-tailed hawks were associated, on average, with steep, north-facing slopes (x̄ = 17.4°, SD = 8.1) and dense understories. At the midscale, goshawks were consistently associated with patches of continuous forest and level terrain within 645 m of nest sites. Red-tailed hawks were associated with nonforested areas located within 105–645 m of nest sites and steep slopes within 105 m of nest sites. Forest fragmentation was greater around red-tailed hawk nest sites, and forested regions were more aggregated around goshawk nest sites when compared with the other species. These patterns indicate that on the Kaibab Plateau, red-tailed hawks will gain habitat at the midscale and goshawks will lose habitat at both scales if forests are fragmented and mature forest structure is lost.

Activity patterns of nesting Mexican Spotted Owls

We collected 2,665 hr of behavioral information using video surveillance on 19 Mexican Spotted Owl (Strix occidentalis lucida) pairs between 25 April and 26 July 1996. Prey deliveries per day increased as the nesting season progressed, with an average of 2.68 prey deliveries during incubation, 4.10 items during brooding, and 4.51 items during the nestling phase. The highest delivery rates were concentrated between l-3 hours before sunrise (02:00-05:00) and l-3 hours after sunset (18:00-21:00). Trip duration during diurnal hours increased 14 fold from incubation through the nestling phase, compared with a 7.2 fold increase during nocturnal hours. Nest bout duration decreased during both diurnal (36%) and nocturnal hours (76%) across the nesting season. Nest attentiveness decreased as the nesting season progressed, from 97% during the incubation phase to 47% during the nestling phase. Owls attended nests at higher rates during diurnal hours than nocturnal hours across all nesting phases. Activity patterns of Mexican Spotted Owls showed marked cyclical changes in response to ecological factors. Fluctuations in nesting behavior were related to changes in nesting phase and time of day.

Canopy closure around nest sites of Mexican spotted owls in northcentral Arizona

We analyzed variation in canopy closure around 47 Mexican spotted owl (Strix occidentalis lucida) nest sites and 47 random forest sites on the Coconino National Forest in northcentral Arizona. We mapped distinct habitat polygons on 1:15,840 color aerial photographs, assigned each polygon to one of 4 canopy-closure classes ( 70%), and measured the area in each canopy class within 5 concentric analysis zones with radii of 0.1, 0.4, 0.8, 1.2, and 1.6 km (delineating rings of about 4, 47, 150, 252, and 352 ha). Landscape composition differed between spotted owl nest and random sites (P 70% canopy-closure class and less area in the 70% canopy predominated. Nesting spotted owls selected areas with denser canopy than randomly available forest landscapes, but outside the immediate nest area (>0.8 km) canopy closure approached that of the surrounding forest.

Clinial genetic variation at enzyme loci in bald eagles (Haliaeetus leucocephalus) from the western United States

Five polymorphic enzyme loci of about 50 sampled were discovered in blood extracts of bald eagles from Alaska, Washington, Oregon, and Arizona, representing the first biochemical genetic variation described for the species. All five loci exhibited trends of north-to-south clinical geographic variation in gene frequencies. Gene frequencies at three loci culminated in fixation in the Arizona population, which consists of 12 known breeding pairs. The Arizona birds were maximally heterozygous at the other two loci, suggesting the possibility of maintenance of some clines by natural selection. No significant discontinuities in gene frequencies were observed which correlated with earlier descriptions of two subspecies (northern and southern races) of bald eagles.

Logging truck noise near nesting northern goshawks

We measured noise levels of four logging trucks as the trucks passed within approximately 500 m of two active northern goshawk (Accipiter gentilis) nests on the Kaibab Plateau in northern Arizona in 1997. Neither a brooding adult female nor a lone juvenile exhibited any discernable behavioral response to logging truck noise, which peaked at 53.4 and 50.3 decibels (dBA). Spectral analysis showed most of the truck sound energy was in the vicinity of 80 Hz.

Summer diet of the peregrine falcon in faunistically rich and poor zones of Arizona analyzed with capture-recapture modeling

Abstract We collected prey remains from 25 Peregrine Falcon (Falco peregrinus) territories across Arizona from 1977 to 1988 yielding 58 eyrie-years of data. Along with 793 individual birds (107 species and six additional genera), we found seven mammals and nine insects. In addition, two nestling peregrines were consumed. We found a larger dependence upon White-throated Swifts (Aeronautes saxatalis) and birds on migration in northern Arizona, while in southeastern and central Arizona average prey mass was greater and columbiforms formed the largest dietary component. In northern, central, and southeastern Arizona, 74, 66, and 56 avian prey taxa, respectively, were recorded. We used capture-recapture modeling to estimate totals of 111 ± 9.5, 113 ± 10.5, and 86 ± 7.9 (SE) avian taxa taken in these same three areas. These values are counterintuitive inasmuch as the southeast has the richest avifauna. For the entire study area, 156 ± 9.3 avian taxa were estimated to be taken by peregrines. Dieta Estival de Falco peregrinus en Arizona Comparando Zonas Ricas y Pobres en Avifauna Mediante un Modelo de Captura-Recaptura Resumen. Desde 1977 a 1988 colectamos restos de presas en 58 nidos de Falco peregrinus a través de Arizona. Conjuntamente con 793 aves individuales (107 especies y seis géneros adicionales), encontramos siete mamíferos y nueve insectos. Además, fueron consumidos dos pichones de Falco peregrinus. En la zona norte encontramos una mayor dependencia sobre Aeronautes saxatalis y aves en migración, mientras que en las zonas sureste y central la masa promedio de presa fue más grande y los columbiformes constituyeron el componente principal de la dieta de Falco peregrinus. En las zonas norte, central y sureste se registraron 74, 66 y 56 taxa de aves presa, respectivamente. Para estimar el número total de taxa capturados por Falco peregrinus usamos un modelo de captura-recaptura. Los valores calculados fueron 111 ± 9.5, 113 ± 10.5 y 86 ± 7.9 (EE) taxa para las zonas norte, central y sureste, respectivamente. Estos valores no reflejan los que esperábamos, ya que la zona sureste tuvo una avifauna más rica. Se estimó que 156 ± 9.3 taxa fueron capturados por Falco peregrinus en la totalidad del área de estudio.

WINTERING BALD EAGLE TRENDS IN NORTHERN ARIZONA, 1975–2000

Abstract Between 1975 and 2000, 4,525 sightings of wintering bald eagles (Haliaeetus leucocephalus) were recorded at Mormon Lake in northern Arizona. Numbers of wintering eagles fluctuated little in the 20 years from 1975 through 1994 (5.5 ± 3.0 mean sightings per day). However, during the winters of 1995 through 1997 local record highs of 59 to 118 eagles increased mean sightings per day to 22.4 ± 9.6. This dramatic population increase led to a major change in social behavior favoring consistent communal roosting; maximum roost counts of 2 to 8 eagles scattered among 11 roosts in prior years shifted to maximums of 33 to 45 eagles regularly using 2 roosts during 1996 and 1997. Winter population averaged 58% adults and 42% immatures, but during 5 recent years of greatest numbers (≥40 eagles in 1989, 1995 through 1997, and 2000), the proportion of immatures increased to 58%. Local increases in the wintering eagle population at Mormon Lake were largely attributable to this greater proportion of immature bald eagles. Both age classes peaked in February, with adults more abundant during October through December and immatures more abundant from January through April. Weekly maximum counts for 1995 through 1997 indicated changing weather and prey conditions resulted in annual variation in local numbers and habitat use of wintering bald eagles.

Bald Eagle Predation on Double-Crested Cormorant and Herring Gull Eggs

Bald Eagles (Haliaeetus leucocephalus) are known predators of adults and juveniles of many species of colonial waterbirds, including gulls (Larus spp.), terns (Sterninae), cormorants (Phalacrocorax spp.), pelicans (Pelecanus spp.), and herons (Ardea spp.; Todd et al. 1982, Norman et al. 1989, Hobson 1997, Wright 2004, Buchanan and Watson 2010). Direct predation by Bald Eagles has caused local population declines in many of these species (Chatwin et al. 2002; Carter et al. 2007; Hayward et al. 2010). Disturbance by Bald Eagles has also been linked to facilitation of egg predation of colonial waterbirds by American Crows (Corvus brachyrhynchos) and Herring Gulls (L. argentatus) (Verbeek 1982, S. Windels unpubl. data). Direct predation by Bald Eagles on eggs of colonial waterbirds has been observed for a few marine species (e.g., Glaucous-winged Gulls [L. glaucescens]; Thompson 1989, Hayward et al. 2010) but evidence is lacking for freshwater species. Here, we report repeated Double-crested Cormorant (P. auritus) and Herring Gull egg predation events by Bald Eagles on a Double-crested Cormorant–Herring Gull rookery in Rainy Lake along the U.S.–Canada border between Voyageurs National Park (VNP), MN, and Ontario, Canada. On 19 July 2011, as part of an ongoing long-term study (Pittman et al. 2015), we visited a Bald Eagle nest (Nest 266, West Fox Island III) in the Fox Islands, Rainy Lake, MN (48u37.2849N, 92u58.3989W) to band nestlings, but the nest had recently failed. We found fragments from several Herring Gull and Double-crested Cormorant eggs under the nest tree, suggesting that the eggs had been brought back to the nest as food for the nestlings. This nest site was ,1100 m from an active Herring Gull and Doublecrested Cormorant rookery (328 pairs Double-crested Cormorants and 38 pairs of Herring Gulls in 2011 [S. Windels unpubl. data]) on the Seven Sisters Islands, Rainy Lake, Ontario (48u37.8669N, 92u58.3329W). We returned to this eagle nest site on 28 July 2011 to search for additional signs of egg predation. We searched around the base of the nest tree for 10 min and found several Herring Gull feathers but no additional gull or cormorant eggs. Another nearby eagle nest (Nest 209, West Fox Island II, MN; 48u37.5669N, 92u57.9669W), ,700 m from the rookery, was briefly occupied by another breeding pair in April–June of 2011 and