Richard T. Reynolds

Sexual Dimorphism in Accipiter Hawks: A New Hypothesis

morphism from vulturine species, through the intermediate mammalian and insect-feeding predators, to the extreme found in the highly active bird-capturing hawks (e.g., certain accipiters and falcons). Most of the theories offered in explanation of reversed sexual dimorphism can be categorized into two groups: (1) those which propose that the condition arose as an adaptation reducing intraspecific competition by creating differential feeding habits of the sexes (Briill 1937; Hagen 1942; Dementiev 1951; Storer 1955, 1966; Selander 1966); and (2) those that cite the need of female dominance to prevent the occurrence of filicidal behavior by the male (Hagen 1942; Amadon 1959). Another aspect of female dominance, proposed by Cade (1960), and presently accepted by Brown and Amadon (1968), is that dimorphism arose in response to the need of female dominance of the male in order to maintain him in his role

Post‐Fledging Survival Of Northern Goshawks: The Importance Of Prey Abundance, Weather, And Dispersal

Effective wildlife conservation strategies require an understanding of how fluctuating environmental conditions affect sensitive life stages. As part of a long-term study, we examined post-fledging and post-independence survival of 89 radio-marked juvenile Northern Goshawks (Accipiter gentilis) produced from 48 nests in northern Arizona, USA, during 1998-2001. Information-theoretic methods were used to examine within- and among-year variation in survival relative to environmental (prey abundance, weather), territory (hatching date, brood size), and individual (gender, body mass) sources of variation. The results support age- and cohort-specific differences in survival that were best explained by behaviors occurring at distinct stages of juvenile development, annual changes in the density of primary bird and mammal prey species, and gender-related differences in body mass. Survival between fledging and independence increased linearly with age and varied among annual cohorts of radio-marked juveniles from 0.81 (95% CI = 0.60-0.93) to 1.00 (95% CI = 0.95-1.00) in association with annual differences in prey density; the slope coefficient for the additive effect of prey density on survival was 1.12 (95% CI = 0.06-2.19). Survival declined to 0.71 (95% CI = 0.60-0.93) shortly after juveniles initiated dispersal (weeks 8-12 post-fledging) and moved to more open habitats at lower elevations. Survival was not closely associated with weather or territory-level parameters. A comparison of the predictions of environmental-, territory-, and individual-based models of survival demonstrated that food availability was the primary factor limiting juvenile survival. This finding indicates that forest management prescriptions designed to support abundant prey populations while providing forest structural conditions that allow goshawks to access their prey within breeding areas should benefit juvenile survival.

EFFECTS OF RADIOTRANSMITTERS ON NORTHERN GOSHAWKS: DO TAILMOUNTS LOWER SURVIVAL OF BREEDING MALES?

Abstract We used the Cormack-Jolly-Seber model to estimate the effects of radiotransmitters on survival of breeding northern goshawks (Accipiter gentilis). We separately compared apparent annual survival of leg-banded goshawks with (1) tailmount- and (2) backpack-style radiotransmitters (hereafter tailmounts and backpacks) to apparent annual survival of breeding adults with legbands only. The best model without radiotransmitter effects, evaluated with Akaikes Information Criterion (AICc), suggested no gender- or year-specific effects on survival. We then added radiotransmitter attachment type (tailmount or backpack) and mass of radiotransmitter as covariates to the base model to estimate the effect of radiotransmitters. Tailmounts on males significantly reduced apparent annual survival from 0.75 (SE = 0.02, 95% CI: 0.71 to 0.78) without radiotransmitters to 0.29 (SE = 0.15, 95% CI: 0.09 to 0.63) with radiotransmitters. Backpacks had no significant effect on survival of adults (0.79, SE = 0.17, 95% CI: 0.33 to 0.97). The strikingly lower survival of goshawks with tailmounts was surprising because tailmounts weighed less (10 g, 1.5% body mass) than backpacks (16–23 g, max = 3.4% body mass) and likely were carried for shorter periods. Due to the small number of goshawks with tailmounts (n = 14) in this study, our results possibly were due to chance. We therefore recommend additional study of the effects of tailmounts on survival of breeding male northern goshawks.

A non-parametric, supervised classification of vegetation types on the Kaibab National Forest using decision trees

Traditional land classification techniques for large areas that use Landsat Thematic Mapper (TM) imagery are typically limited to the fixed spatial resolution of the sensors (30 m). However, the study of some ecological processes requires land cover classifications at finer spatial resolutions. We model forest vegetation types on the Kaibab National Forest (KNF) in northern Arizona to a 10-m spatial resolution with field data, using topographical information and Landsat TM imagery as auxiliary variables. Vegetation types were identified by clustering the field variables total basal area and proportion of basal area by species, and then using a decision tree based on auxiliary variables to predict vegetation types. Vegetation types modelled included pinyon-juniper, ponderosa pine, mixed conifer, spruce- and deciduous-dominated mixes, and openings. To independently assess the accuracy of the final vegetation maps using reference data from different sources, we used a post-stratified, multivariate composite estimator. Overall accuracy was 74.5% (Kappa statistic = 49.9%). Sources of error included differentiating between mixed conifer and spruce-dominated types and between openings in the forest and deciduous-dominated mixes. Overall, our non-parametric classification method successfully identified dominant vegetation types on the study area at a finer spatial resolution than can typically be achieved using traditional classification techniques.

Juvenile movement and natal dispersal of Northern Goshawks in Arizona

Abstract We investigated the departure, transient movement, and local settlement stages of natal dispersal in a population of Northern Goshawks (Accipiter gentilis) on the Kaibab Plateau of northern Arizona. The study included 614 color-banded juveniles produced at 555 nests during 1991–2003, 89 of which were radio-marked during 1998–2001. Radio-marked juveniles initiated dispersal between 71 and 103 days posthatching, and spent between 33 and 66 days in the natal territory after fledging. Our best-fitting proportional hazards models predicted the timing of dispersal as a function of annual differences in the density of primary bird and mammal prey species, weather conditions, and natal brood size. Once dispersal was initiated, most juveniles moved into the more open habitats that surrounded the study area and few eventually returned to breed; first-year fidelity to the local natal population was 28%, and only 69 (11%) color-banded juveniles had entered the territorial population by 2004. Median natal dispersal distance on the Kaibab Plateau was 15.0 km (range  =  0.1–58.1 km), a distance equivalent to about four times the diameter of an average breeding territory (3.8 km). Local settlement behavior of Northern Goshawks appeared to be driven by a combination of intraspecific competition for a limited number of breeding opportunities and inbreeding avoidance. However, much of the natal dispersal process operated at broad spatial scales beyond our study population, indicating a potentially high level of demographic connectivity among naturally fragmented breeding populations in the American Southwest.

An Improved Extraction Method to Increase DNA Yield from Molted Feathers

Abstract To assess the value of molted feathers as a noninvasive source of DNA for genetic studies of Northern Goshawks (Accipiter gentilis), we isolated and quantified DNA from molted feathers and compared yields across five feather types. We also compared PCR success across the same five feather types using five microsatellite genetic markers of varying size. In addition, we compared DNA yields from a commonly used extraction method versus one we modified to increase DNA yield. Results indicated molted feathers provided on average 24 ng μl−1 of DNA, which is a relatively high DNA yield compared to other noninvasive tissue sources. Tail feathers yielded significantly more DNA than primary, secondary, and smaller feathers, yet all feather sizes produced equally high rates of PCR success. Although our modified extraction method increased the time required for processing feathers, it resulted in significantly higher yields of DNA as compared to the unmodified protocol.

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.

RETURN RATE, FIDELITY, AND DISPERSAL IN A BREEDING POPULATION OF FLAMMULATED OWLS (OTUS FLAMMEOLUS)

Abstract We estimated annual return rate, fidelity, and breeding dispersal in a migratory population of Flammulated Owls (Otus flammeolus) in central Colorado. Return rates, based on capture-recapture histories of 39 males and 52 females from 1981 to 2003, were higher for males (84%) than for females (45%). Annual recapture probability was higher for females, because breeders are easier to capture than nonbreeders and females always attempted to nest, whereas some males were unpaired (did not nest) for up to four years. Territory fidelity was male biased (92%, vs. 56% for females, adjusted for undetected emigration), and mean tenure on territories was more than twice as long for males as for females. Females, but not males, had lower return rates to territories in the year following nesting failure compared with females whose nests were successful. Most males appeared to occupy one territory their entire reproductive lives, countering predictions of habitat-selection models that individuals should move to higher-quality habitats when they become available. We estimated that 74% of pairs retained the same mate in consecutive nesting attempts, but mates that bred together for multiple years had no reproductive advantages over mates that bred together for the first time. In most cases, females dispersed from territories if their mates did not return. When females dispersed, they went to territories where total productivity over the study and lifetime reproductive success of new mates were higher than on original territories, which supports the hypothesis that dispersal by females increases individual fitness. Tasa de Retorno, Fidelidad y Dispersión en una Población Reproductiva de Otus flammeolus

Genetic Evidence for Low Frequency of Extra-Pair Fertilizations in Northern Goshawks

We collected blood for allozyme analysis from Northern Goshawks (Accipiter gentilis atricapillus) on the Kaibab Plateau in northern Arizona during 1991-1993 to quantify frequency of extra-pair fertilizations (EPFs). Northern Goshawks are socially monogamous, territorial, noncolonial, synchronous breeders, and their nests are relatively far apart, characteristics that suggest that EPFs should be low. We sampled 103 adults and 122 nestlings from 64 nests. Both putative parents were sampled at 39 nests, but we were able to capture and sample only one putative parent at 25 other nests (84%, female only; 16%, male only). Of the 39 complete families sampled, only 1 of 77 (1.3%) nestlings (or in 1 of 39 clutches, 2.6%) had a genotype not consistent with both parents; the male was excluded as the genetic father of this nestling. When this estimate was adjusted based upon the probability of excluding a putative father when he is not the actual father, the estimate of nestlings sired by EPFs was 9.4% in 1991 and zero in 1992 and 1993. There was no evidence of egg-dumping. Our data suggest that EPFs are infrequent in Northern Goshawks breeding in northern Arizona, a result consistent with characteristics of their mating system.

Lifetime Reproduction of Flammulated Owls in Colorado

ABSTRACT We investigated lifetime reproductive success (LRS) of 22 male and 46 female adult Flammulated Owls (Otus flammeolus) in Colorado from 1981–2003. Sexual differences in LRS were at least partially attributable to incomplete breeding histories of females, due to females having a higher estimated emigration rate from the study area than males. The mean number of lifetime breeding attempts for males was 3.4 ± 0.6 (SE; range  =  1–12), and for females it was 1.9 ± 0.3 (range  =  1–8). Adjusted for emigration beyond the study area, the estimated mean number of lifetime breeding attempts was 3.6 for males and 2.5 for females. The mean number of lifetime successful breeding attempts (fledging at least one owlet) was similar to lifetime breeding attempts for each sex, reflecting the fact that 84% (85 of 101) of all breeding attempts were successful. Breeding lifespan was correlated with lifetime reproduction for both sexes. Males tended nests that produced 6.9 ± 1.2 fledglings over 4.3 ± 0.8 yr, while females produced 4.0 ± 0.6 fledglings over 2.0 ± 0.3 yr; adjusted for emigration beyond the study area, males tended nests that produced 7.2 fledglings over 4.5 yr, while females produced 5.2 fledglings over 2.6 yr. Relatively few individuals of each sex produced most of the offspring, as 18% of females and 24% of males produced 50% of total owlets. Our finding that relatively few adults accounted for most offspring appears to be associated with habitat quality in territories. Flammulated Owls tend to have a life-history strategy similar to larger raptors by having a relatively low annual reproductive rate and a relatively long lifespan.