Thesis (M.Sc.)--Acadia University, 1999. / Includes bibliographical references (leaves 68-71). Also available on the Internet via the World Wide Web.

Abstract I studied the ecology of the goshawk-grouse relationship in Oulu, northern Finland, during and outside the breeding season, by radio-telemetry. This included museum samples of goshawk to obtain a better ecological as well as a better evolutionary understanding of it. The proportion of grouse in the diet of goshawks has decreased since the 1960's, in accordance with the decline of grouse populations. The main prey groups replacing the lacking grouse were corvids, squirrels and hares. The proportion of grouse was highest in spring and it decreased towards the end of the nestling phase. The most preferred grouse species were hazel grouse Bonasa bonasia and willow grouse Lagopus lagopus. Preferences for different prey types are not explained by active choices of goshawk, but by changes in the vulnerability of the prey species. The nestling phase, when food demand is highest, is not adjusted to when prey supply is highest, but before it. The size and shape of the goshawks has changed from the 1960's. Adult males became smaller but females larger. Both became relatively longer winged and tailed. Decrease of male's size may be a response to the change in the food supply. Prey types replacing grouse are generally smaller, which may cause the change in the male's morphology. Females being less active during the breeding season may not be affected. For the female to be larger is advantageous in winter when they kill 'over large' prey like mountain hares Lepus timidus and capercaillie cocks Tetrao urogallus. Wintering goshawks were mainly females in adult plumage that tended to stay in the study area. However, only one third bred locally. More than one quarter of all hawks died during the study. Although known to be inhabitants of old forests, which this study supports, goshawks are fairly well adapted to mosaic landscape resulting from modern forestry, providing that suitable sized prey is available. Females have less problems, probably because hares, the main winter prey for females, are not affected negatively by forestry, like grouse and squirrels are, the main prey for males. Goshawks have a remarkable impact on grouse populations, especially when non-territorial hawks, 'floaters' are also included. About one half of the total mortality rate of grouse may be due to goshawk predation. Goshawk predation accords to predictions of general predation theory and may be a noticeable factor contributing to cyclicity in grouse.

The ability of northern goshawks (Accipiter gentilis) to persist in intensively managed and selectively harvested forest habitats is largely unknown. To address the concern that populations of northern goshawks in eastern Oregon may be declining in response to habitat alteration, I studied occupancy rates and habitat relationships of nesting goshawks on the Fremont National Forest and adjacent private lands during 1992-1994. My objectives were to determine if historic territories (i.e., those occupied ��� 1 season during 1973-1991) were still occupied, document current site conditions and quantify changes in forest cover on those territories between 1973-1994, and compare present conditions of forest vegetation between nest sites that were currently occupied and those where I did not detect the presence of territorial goshawks (no-response sites). In 1994, I surveyed a forest-wide random sample of 51 historic nest sites, stratified by forest cover type. Occupancy of historic sites by goshawks was 29% (15 of 51), compared to 79% (30 of 38) mean annual occupancy rate of current territories (found initially during 1992-1994). Across all strata, 86% of current nest sites (n=38) were in Mid-aged or Late structural stage forest (trees >23 cm DBH) with >50% canopy closure. Among the historic territories used for analysis (n=46), those found occupied (n=15) in 1994 had significantly more Mid-aged Closed forest (average stand DBH 23-53 cm, <15 trees per ha >53 cm DBH; >50% canopy closure) and Late Closed forest (15 trees per ha >53 cm DBH; >50% canopy closure) than no-response sites (n=31). This relationship was significant (P<0.05) for circular scales of 12, 24, 52, 120, and 170 ha surrounding goshawk territory centers. Within the 52 ha scale around historic nest sites surveyed in 1994, occupied sites had 49% (SE=6.6) total Late Closed and Mid-aged Closed forest, while sites with no response had 19% (SE=3.0) total Late and Mid-aged Closed forest. Historic sites had 51% (SE=3.8) total Late and Mid-aged Closed forest when last known occupied before 1992. Among historic territories, mean percent area of habitat in Late Closed forest at the 12 ha nest stand scale was 4 times greater in occupied (27%) than in no-response sites (6%) (P<0.05). A logistic regression model for occupied sites confirmed the importance of Late Closed and Mid-aged Closed forests as indicators of quality habitat within the 52 ha scale on historic sites where goshawks were still present in 1994. Goshawk pairs were more likely to persist in historic territories having a high percentage of mature and older forest (about 50%) in closed-canopied conditions within the 52 ha scale, suggesting that little or no habitat alteration within aggregate nest stands is important to ensure the persistence of nesting pairs. I recommend preserving multiple nest stands within the 52 ha scale and discourage further cutting of large, late and old structure trees (>53 cm DBH) within the PFA to preserve stand integrity, maintain closed canopies, maintain connectivity to alternate nest stands, and optimize conditions for breeding goshawk pairs to persist. / Graduation date: 1998

Understanding the role that extrinsic processes play in shaping animal population dynamics and demography is a central tenet of population ecology and an issue of vital importance for conservation and wildlife management. The top-down impact of predation and bottom-up influence of food availability are thought to be two of the most important extrinsic processes affecting population dynamics and demography of species occupying middle trophic levels. However, many studies only focus on quantifying the impact of one of these processes in isolation and it is not clear whether the impact of one extrinsic factor on population dynamics and demographic rates is augmented or lessened by changes in other extrinsic factors. In this thesis I examine the extent to which both top-down and bottom-up processes shape population dynamics (population size, recruitment and immigration) and demography (survival, reproduction, life-history trade-offs and reproductive strategies) in a long-lived species, the tawny owl, by taking advantage of a natural increase in predation risk (goshawk abundance) and a decline in food availability (field vole densities). Despite the increase in predation and the decline in food availability, the owl population remained stable, which we posit is due to goshawk predation being selective on individuals with a low reproductive value (juveniles and old individuals) and an increasing number of immigrants entering the population. Selective predation on older owls had a negative impact on the survival of this age class and appeared to be shaping the pattern of actuarial senescence and influencing the strength of the intrinsic trade-off between survival and reproduction. As food availability declined and predation risk increased owls appeared to be switching from an 'eggs in one basket strategy' of saving resources to invest more in fewer breeding attempts in the future, to a 'bet-hedging' strategy of reproducing more often, but investing less per breeding attempt.

The identification of resources animals select provides valuable insight into the factors that limit populations and control distributions. My objective in this thesis was to examine how the northern goshawk (Accipiter gentilis atricapillus) selects resources during the nesting and fledging life-history stages. This work was conducted in southeastern British Columbia, Canada, from 1998 to 2006. Using Information-Theoretic techniques, I described the forest characteristics selected by goshawks when locating their nest sites within their breeding territories, and the forest characteristics selected by fledgling goshawks around the nest while they are still dependent on their parents for food. I found that goshawks select nesting sites with a relatively large amount of high canopy cover (>40%) forest within 200 m of the nest. The amount of high canopy cover forest remained higher than comparison points up to 1100 m from the nest, but goshawks also will select for forest openings relatively close to the nest (- 174 m). Fledgling goshawks selected for continuous areas of forest cover, particularly areas with higher amounts of forest between 40-80 years old within 525 m distance from the nest. Presumably, goshawks selected these younger stands in order to avoid predation. Fledglings also selected areas with more high canopy cover forest and areas without large amounts of recently-harvested forest (<10 years of age) stands within 525 m of the nest. Thus, the structural characteristics of forests required by goshawks for nesting are complex, and different competing characteristics are selected at different distances from the nest. Although goshawks do require mature forest stands with high canopy cover close to the nest, a greater diversity of forest types appears to be either tolerated or required as the distance from the nest increases. Additionally, limited evidence suggests that the movements of fledgling goshawks may be governed by a combination of forest structure and inter-familiar interactions.

The Northern Goshawk has been a species of concern since its decline in the early 1990s, which has been attributed in part to loss of critical breeding and wintering habitat. Nest site selection of goshawks has been correlated with certain specific site characteristics including, but not limited to, forest species composition, forest stand size, diameter of nest tree, percent cover, tree height, site slope, and aspect. The goshawk holds the status of a Management Indicator Species (MIS) on all of the six national forests in Utah. This status requires annual monitoring to track goshawk numbers and to address any activities on the forests that may affect nest site activity. Findings from the annual nesting data showed that some territories have been more active than others. We summarized the data from the three national forests in southern Utah in order to understand differences in nesting habitat among the forests. We also analyzed the nesting habitat variables slope, elevation, and nest tree species statistically to determine if they could be used as predictors of nest activity. We found that slope and elevation were not good predictors while nest tree species was significant in its ability to predict nest activity. We concluded the nesting habitat variables we selected were insufficient in their ability to predict nest activity and other variables such as prey species availability, weather conditions in the spring, and forest cover type might be needed to create a model that more accurately predicts nest activity.