Ryan J. Fisher

From Wiens to Robel: A Review of Grassland-Bird Habitat Selection

Abstract Efforts to stabilize or increase grassland bird populations require identification of suitable habitat as a first step. Although the number of studies examining grassland-bird habitat selection has increased substantially in recent years, much uncertainty exists regarding local-scale habitat variables that researchers should consider. We reviewed 57 studies and identified important vegetation features correlated with grassland bird abundance, density, occurrence, and nest and territory selection. Our objectives were to 1) guide future studies of grassland-bird habitat use by providing a reduced set of relevant vegetation characteristics, 2) challenge researchers to critically think about what variables to consider, and 3) highlight the need to include consistent definitions of terms used to describe grassland bird habitat. We identified 9 variables that were important predictors of habitat use by grassland birds: coverage of bare ground (important in 50% of the instances where it was included), grass (34% of instances), dead vegetation (33% of instances), forbs (31% of instances), and litter (29% of instances), along with an index of vegetation density (39% of instances) and volume (39% of instances), litter depth (36% of instances), and vegetation height (41% of instances). Only 25% of studies provided information on effects sizes and measures of variance. Furthermore, definitions of measured habitat variables were not consistent among studies. We provide definitions of the 9 important variables and implore authors to report effect size and measures of variance. Standardization of terms and reporting of meaningful results will facilitate replication of wildlife research and enhance our ability to recognize general patterns that emerge from observational studies of habitat use.

Effects of Sex and Age on Survival of Northern Flickers: a Six-Year Field Study

Abstract Although many forestry management strategies rely on population estimates of indicator species such as woodpeckers (Picidae), empirical estimates of demographic parameters within this taxon are few. We used program MARK to assess influences of age and sex on apparent survival of adult Northern Flickers (Colaptes auratus) from a six-year mark-recapture study. The top model suggested no differences in apparent survival between the sexes with an overall survival estimate of 0.43 (95% CI: 0.38–0.48). Other models suggested that recapture efficiency differed between the sexes (males: 0.87; females: 0.78), perhaps because males were more philopatric to nest sites. We suggest that high parental investment by male flickers relative to other taxa such as passerines may lead to relatively equal mortality rates between the sexes, rather than the common pattern of female-biased mortality. Survival rates relative to age were constant at least up to the age of three years. Overall, flickers appear to have lower survival than some other woodpecker species and may invest relatively heavily in current reproduction.

Comparing food limitation among three stages of nesting: supplementation experiments with the burrowing owl

Abstract Food availability is an important limiting factor for avian reproduction. In altricial birds, food limitation is assumed to be more severe during the nestling stage than during laying or incubation, but this has yet to be adequately tested. Using food-supplementation experiments over a 5-year period, we determined the degree and timing of food limitation for burrowing owls (Athene cunicularia) breeding in Canada. Burrowing owls are an endangered species and food limitation during the nestling stage could influence reproductive performance of this species at the northern extent of their range. Supplemented pairs fledged on average 47% more owlets than unfed pairs, except during a year when natural food was not limiting (i.e., a prey irruption year). The difference in fledgling production resulted from high nestling mortality in unfed broods, with 96% of all nestling deaths being attributed to food shortage. Supplemental feeding during the nestling period also increased fledgling structural size. Pairs fed from the start of laying produced the same number of hatchlings as pairs that received no supplemental food before hatch. Furthermore, pairs supplemented from egg laying to fledging and pairs supplemented during the nestling period alone had the same patterns of nestling survival, equal numbers of fledglings, and similar fledgling mass and structural size. Our results provide empirical support for the hypothesis that the nestling period is the most food-limited phase of the breeding cycle. The experimental design we introduce here could be used with other altricial species to examine how the timing of food limitation differs among birds with a variety of life-history strategies. For burrowing owls, and other species with similar life histories, long-term, large-scale, and appropriately timed habitat management increasing prey abundance or availability is critical for conservation. Our results provide empirical support for the hypothesis that the nestling period is the most food-limited phase of the breeding cycle. For burrowing owls, and other species with similar life histories, long-term, large-scale, and appropriately timed habitat management increasing prey abundance or availability is critical for conservation.

Post-fledging Movements of Sprague's Pipit

Abstract Spragues Pipit (Anthus spragueii) is a threatened grassland songbird that has been described as one of the least known species in North America. We attached radio transmitters to 19 Spragues Pipit nestlings in south-central Saskatchewan in 2004 and 2005 as part of a study to quantify post-fledging movements. Eleven juveniles died before leaving the nest (58%) and five survived for at least 9 days. Predation was the most common cause of mortality of young pipits both before and after fledging. Distances moved between days steadily increased but fledglings typically remained within 100 m of their nest during the first week post-fledging. Movement by fledglings after the first week were typically >100 m.

Roost Selection and Roosting Behavior of Male Common Nighthawks

Abstract Many studies to date have documented clear energetic costs and benefits of avian roost selection. Male Common Nighthawks (Chordeiles minor) spend at least half of each day during the summer on a day-roost. Therefore selection of roost-sites likely has implications for survival and long-term fitness. Our objective was to identify characteristics of day-roosts used by male Common Nighthawks in Cypress Hills Provincial Park, Saskatchewan, Canada. We measured features of roost trees and monitored behavior of roosting birds. Nighthawks preferred trees situated on north facing slopes surrounded by trees with significantly lower canopy height compared to randomly measured trees. Roost trees were taller than random trees and occurred in less dense patches of forest. Birds always roosted parallel to branches and adopted a motionless posture. There was a non-significant trend for birds to roost on branches facing east. Birds typically roosted in a direction pointing away from the sun and away from the roost tree trunk. Roost trees emerging from the canopy may provide landmarks for birds as they search for suitable day-roosts, whereas a low tree density surrounding roost trees likely reduces flight costs associated with maneuvering. Our results suggest that roosts chosen by male nighthawks may provide selective benefits in terms of microclimate, energetics and predator avoidance, but further studies are needed to determine which is the most important.

Habitat use by Sprague's Pipits (Anthus spragueii) in Native Pastures and Planted, Non-Native Hay Fields

ABSTRACT. The addition of planted grasslands (i.e., fields that have been planted with exotic grass and forb species) to the North American landscape has been beneficial for the conservation of many species, but not necessarily for species that show a preference for native grasslands. Under what conditions these planted fields are attractive to native grassland specialists is unclear. Spragues Pipit (Anthus spragueii) is a native grassland specialist, but it breeds in planted grasslands in some parts of its range. We conducted a comparative study of territory and nest use by Spragues Pipits in native pastures and planted hay fields from 2006 to 2008. In planted hay fields, territories were characterized by vegetation height of 25 cm and litter depth of <1.5 cm; in native pastures, the birds used territories with 15% bare ground and <1.5 cm litter depth. Nests in both habitats were located in areas with vegetation height of 25–30 cm, whereas random areas had either taller or shorter vegetation. Territories were associated with different vegetation characteristics in both habitats. Spragues Pipits used the same nest characteristics in both habitat types, which suggests that they found areas within planted grasslands that closely resembled areas that they might use for nesting in native grasslands. Planted fields with a low amount of alfalfa and suitable vegetation height (20–30 cm) should be attractive to breeding Spragues Pipits.

INVESTMENT IN NEST DEFENSE BY NORTHERN FLICKERS: EFFECTS OF AGE AND SEX

Abstract At early breeding stages, male woodpeckers invest heavily in nest construction and defense, but parental contributions to brood defense among Picidae are not well known. We studied the Northern Flicker (Colaptes auratus) to determine whether sex, age, brood size, body size, or body condition influenced defense behavior. When presented with a model predator (red squirrel, Tamiasciurus hudsonicus) during the brood-rearing period, parents exhibited a range of behaviors, such as blocking the nest hole, diving at the model, and striking the model; however, defense scores did not differ between males and females aged 1, 2, or 3+ years old. Although we predicted that defense level would be positively correlated with brood size, we found no such relationship. Adult body size and condition also were not related to defense intensity. We conclude that the sexes may exhibit similar levels of defense because they have similar apparent annual survival rates and males are only slightly larger than females. If flickers optimize clutch size according to the number of offspring they can rear, then there may be no relationship between defense and brood size.

Apparent survival of adult Burrowing Owls that breed in Canada is influenced by weather during migration and on their wintering grounds

ABSTRACT Understanding factors that influence the survival of endangered migratory species is critical for making informed management decisions, yet this understanding relies on long-term recapture datasets for species that are, by definition, rare. Using 3 geographically widespread (Saskatchewan, Alberta, and Manitoba, Canada) and long-term (6–15 yr) mark–recapture datasets, we quantified spatial and temporal variation in apparent annual survival and recapture probabilities of Burrowing Owl (Athene cunicularia), an endangered species that breeds in Canada. We then examined how large-scale weather patterns during migration (storms) and on the wintering and breeding grounds (precipitation), in addition to prey irruptions on the breeding grounds, influenced apparent survival of Burrowing Owls. Female Burrowing Owls had lower apparent survival than males in all 3 study areas. Storms during fall migration and above-average precipitation on the wintering grounds were associated with reduced apparent survival of Burrowing Owls in the longest-running study area, Saskatchewan; in Alberta and Manitoba, there were few correlations between apparent survival of Burrowing Owls and weather or prey irruptions. Increases in stochastic events such as storms during migration or precipitation on the wintering grounds could have adverse consequences on the already small Burrowing Owl population in Canada. Local management actions that focus solely on improving adult apparent survival within Canada are likely insufficient for mitigating susceptibility of adults to inclement weather or other factors outside the breeding season, underscoring the need for management of this species across multiple jurisdictions within North America.

Statistical Confusion Among Graduate Students: Sickness or Symptom?

Abstract Statistics is one of the most important yet difficult subjects for many ecology and wildlife graduate students to learn. Insufficient knowledge about how to conduct quality science and the ongoing debate about the relative value of competing statistical ideologies contribute to uncertainties among graduate students regarding which statistical tests are most appropriate. Herein, we argue that increased education of the available statistical tests alone is unlikely to ameliorate the problem. Instead, we suggest that statistical uncertainties among graduate students are a secondary symptom of a larger problem. We believe the root cause lies in the lack of education on how to conduct science as an integrated process from hypothesis creation through statistical analysis. We argue that if students are taught to think about how each step of the process will affect all other steps, many statistical uncertainties will be avoided.

Ferruginous Hawks Buteo regalis alter parental behaviours in response to approaching storms

AbstractHeavy and frequent rain, low temperatures, and strong winds may decrease adult foraging time, cause thermoregulatory stress on nestlings, and lead to nest damage or destruction, all of which can negatively affect breeding success. However, certain parental behaviours can mitigate these potentially negative effects of inclement weather. We examined how parents could mitigate these negative weather effects by adjusting three behaviours—nest attendance, prey deliveries, and nest maintenance—before, during, and after storms at 11 nests of the at-risk Ferruginous Hawk (Buteo regalis) in Canada. Female adults spent an increasing amount of time on the nest as wind speed increased. Similar numbers of prey were delivered before and after storms, suggesting that Ferruginous Hawks do not compensate for lost foraging time. They appeared to demonstrate an ability to detect approaching storms, possibly by responding to falling barometric pressure cues, and may have mitigated the risk of nest damage by increasing their nest maintenance behaviours. Our study is among the first to observe storm preparation behaviour, and indicates that some raptorial birds have the ability to alter nesting behaviour in response to approaching inclement weather.ZusammenfassungKönigsbussarde (Buteo regalis) verändern das elterliche Verhalten bei heraufziehenden Stürmen Starke und andauernde Regenfälle, niedrige Temperaturen und starke Winde können die Zeit der Nahrungssuche von Adulten verringern. Dies verursacht thermoregulatorischen Stress bei den Nestlingen und kann zu Schaden oder Vernichtung der Brut führen, was insgesamt den Bruterfolg negativ beeinflussen kann. Dennoch können bestimmte elterliche Verhaltensweisen diese potentiell negativen Schlecht-Wetter-Effekte abmildern. Wir untersuchten, wie Eltern diese negativen Wettereinflüsse durch die Anpassung von drei Verhaltensweisen abschwächen konnten: Anwesenheit am Nest, Beuteübergaben und Brutpflege vor, während und nach Stürmen an 11 Nestern des gefährdeten Königsbussard (Buteo regalis) in Kanada. Adulte Weibchen verbrachten mehr Zeit auf dem Nest mit zunehmender Windgeschwindigkeit und stärker werdenden Regenfällen. Vor und nach den Stürmen wurden ähnliche Anzahlen an Beuteobjekten eingetragen, was darauf hindeutet, dass Königsbussarde verlorene Zeiten zur Nahrungssuche nicht kompensieren. Königsbussarde scheinen die Fähigkeit zu haben, heraufziehende Stürme zu erkennen, in dem sie auf fallenden Luftdruck reagieren und das Risiko eines Brutverlustes durch zunehmende Brutpflege minimieren. Unsere Studie gehört zu den ersten, die sturmvorbereitendes Verhalten beobachten konnte und zeigt, dass Greifvögel in der Lage sind, ihr Brutverhalten als Antwort auf raue Witterungsbedingungen anzupassen.