Owl Reproductive Success Research Articles

A Review Of Burrowing Owl (Athene cunicularia) Literature Using Bibliometric Comparisons: Topical Bibliographies and Online Databases

The purpose of this review is to present a brief overview of literature published through 2016 on the Burrowing Owl (BUOW; Athene cunicularia) as an example of how the science of bibliometrics allows us to examine the literature on this species and to determine and display important trends, including gaps in that literature. We conducted various analyses on approximately 1681 BUOW articles to demonstrate the utility of bibliometrics. We also compare the effectiveness of a traditional bibliography versus online databases. The query of even several online databases does not guarantee identifying but a fraction of the total references. Even the most complete database searched for the term “Athene cunicularia” produced only 38% of those of the current World Owl Bibliography Update. Topical areas that seem absent or limited in the published literature include: the genetics of many subspecies of this owl; the population status and trend in intact ecosystems versus human-altered habitats; details on the demography of Burrowing Owls in Central and South America; migratory patterns and overwintering habitat conditions; the dispersal and movement of several metapopulations; successful mitigation strategies; the effectiveness of translocation; the effect of various artificial burrow designs on interior microclimate and owl reproductive success; and a more comprehensive approach to management. This is an ongoing project that will contribute to a larger update of the literature on the owls of the world.

The Relationship between Weather and Reproduction of the Barn Owl Tyto Alba in a Semi-Arid Agricultural Landscape in Israel

Even though the Barn Owl ( Tyto alba) is distributed worldwide, little information is available on how weather affects Barn Owl breeding outside of Europe and North America. For instance, if cold temperatures can negatively influence population dynamics in temperate regions, heat could have a similar negative effect in arid regions. We have studied a breeding population of Barn Owls in a semi-arid agricultural environment over 13 years in Israel in order to determine whether lack of rain and hot ambient temperatures impair Barn Owl reproductive success. The percentage of nest boxes occupied by Barn Owls was not related to any of the weather variables, whereas the number of nestlings per Barn Owl pair and the percentage of pairs that succeeded to fledge young was lower in years when it started to rain later in the season and when the minimum daily temperature was higher during the breeding season. In comparison to temperate regions, heat is detrimental to Barn Owl breeding and early precipitation is probably important in boosting vegetation and, in turn, the abundance of small mammals, the Barn Owl's staple food.

Food availability and predation risk, rather than intrinsic attributes, are the main factors shaping the reproductive decisions of a long-lived predator.

Deciphering the causes of variation in reproductive success is a fundamental issue in ecology, as the number of offspring produced is an important driver of individual fitness and population dynamics. Little is known, however, about how different factors interact to drive variation in reproduction, such as whether an individual's response to extrinsic conditions (e.g. food availability or predation) varies according to its intrinsic attributes (e.g. age, previous allocation of resources towards reproduction). We used 29years of reproductive data from marked female tawny owls and natural variation in food availability (field vole) and predator abundance (northern goshawk) to quantify the extent to which extrinsic and intrinsic factors interact to influence owl reproductive traits (breeding propensity, clutch size and nest abandonment). Extrinsic and intrinsic factors appeared to interact to affect breeding propensity (which accounted for 83% of the variation in owl reproductive success). Breeding propensity increased with vole density, although increasing goshawk abundance reduced the strength of this relationship. Owls became slightly more likely to breed as they aged, although this was only apparent for individuals who had fledged chicks the year before. Owls laid larger clutches when food was more abundant. When owls were breeding in territories less exposed to goshawk predation, 99·5% of all breeding attempts reached the fledging stage. In contrast, the probability of breeding attempts reaching the fledging stage in territories more exposed to goshawk predation depended on the amount of resources an owl had already allocated towards reproduction (averaging 87·7% for owls with clutches of 1-2 eggs compared to 97·5% for owls with clutches of 4-6 eggs). Overall, our results suggested that changes in extrinsic conditions (predominantly foodavailability, but also predator abundance) had the greatest influence on owl reproduction. In response to deteriorating extrinsic conditions (fewer voles and more goshawks), owls appeared to breed more frequently, but allocated fewer resources per breeding attempt. However, intrinsic attributes also appeared to have a relatively small influence on how an individual responded to variation in extrinsic conditions, which indicates that owl reproductive decisions were shaped by a complex series of extrinsic and intrinsic trade-offs.

Range-wide analysis of northern spotted owl nesting habitat relations

Recently the US Fish and Wildlife Service, as part of a critical habitat analysis for the northern spotted owl (Strix occidentalis caurina), developed habitat suitability models based on thousands of owl nest sites distributed across 11 regions using the MaxEnt tool. Because these models formed the basis for critical habitat designations on millions of hectares of land, we undertook an independent evaluation of the FWS effort. We evaluated the accuracy of vegetation data used as input to develop the models, conducted out of sample analyses, correlated model output with owl reproductive success in two study areas, and developed alternate models using two different statistical methods. Vegetation data appeared accurate for only a few variables, and accuracy varied among model regions. Out of sample testing gave a high rate of classification errors and owl productivity was not correlated with MaxEnt model output in two study areas. Alternate statistical methods produced reasonable models with fewer variables. Critically, neither the models compared across regions nor the regions analyzed with different tools led to comparable use of variables. Thus biological interpretation of owl habitat selection models seemed ambiguous. In addition, for MaxEnt and one of the other tools, a highly significant trend by regression was found showing decreasing model accuracy as number of training nest sites increased. Together, these two results suggest that the generated models may be spurious to some unknown degree, perhaps because the underlying vegetation data, also derived from a model, are not sufficiently accurate to support the analysis and/or because the owls themselves affect habitat suitability by consuming their prey base. We suggest that the USFWS exercise caution in using MaxEnt models as a basis for regulatory purposes such as consultation, estimating likelihood of occupancy by owls, or evaluation of site-specific recovery actions.

Reproductive success of Mexican spotted owls (Strix occidentalis lucida) in relation to common environmental noise ― biotic, non-military aircraft, and weather-related

From 2000 to 2005, noise in Mexican spotted owl habitat in the Gila National Forest, NM, was monitored using an array of Larson-Davis (LD) sound level meters (SLMs). Thirty-nine SLMs were deployed across a 20 km x 24 km area, collecting 2-s time interval data mid-April to July, resulting in over 350,000 hr of data. Time-history profiles could be used to attribute many events to sources reliably when SNR exceeded the background by 5-10 dB. The events were categorized as biotic (insects and chorusing birds), thunder, regional commercial jet aircraft, and local air traffic (recreational and firefighting). Measured by the proportion of 2-s samples with LAeq > 60 dB, biotic sources and thunder were the most important. Regional commercial jet traffic was the most significant anthropogenic source, accounting for 2% of the total. Based on cumulative sound exposure, thunder was the greatest contributor. Regression techniques were used to relate owl reproductive success to noise metrics by source. Biotic noise was the only significant correlate, highly and positively related to owl reproductive success. The most reasonable interpretation was a strong relationship between biotic noise and owl prey base [Work supported by U.S. Air Force ACC/CEVP.]

Potential Influences of Climate and Nest Structure on Spotted Owl Reproductive Success: A Biophysical Approach

Many bird species do not make their own nests; therefore, selection of existing sites that provide adequate microclimates is critical. This is particularly true for owls in north temperate climates that often nest early in the year when inclement weather is common. Spotted owls use three main types of nest structures, each of which are structurally distinct and may provide varying levels of protection to the eggs or young. We tested the hypothesis that spotted owl nest configuration influences nest microclimate using both experimental and observational data. We used a wind tunnel to estimate the convective heat transfer coefficient (hc) of eggs in 25 potential nest configurations that mimicked 2 nest types (top-cavity and platform nests), at 3 different wind speeds. We then used the estimates of hc in a biophysical heat transfer model to estimate how long it would take unattended eggs to cool from incubation temperature (∼36°C) to physiological zero temperature (PZT; ∼26°C) under natural environmental conditions. Our results indicated that the structural configuration of nests influences the cooling time of the eggs inside those nests, and hence, influences the nest microclimate. Estimates of time to PZT ranged from 10.6 minutes to 33.3 minutes. Nest configurations that were most similar to platform nests always had the fastest egg cooling times, suggesting that platform nests were the least protective of those nests we tested. Our field data coupled with our experimental results suggested that nest choice is important for the reproductive success of owls during years of inclement weather or in regions characterized by inclement weather during the nesting season.

Influence of prey abundance on northern spotted owl reproductive success in western Oregon

The hypothesis that high temporal variability of northern spotted owl (Strix occidentalis caurina) reproductive success is a response to prey abundance remains largely untested. We evaluated this relationship in the Oregon Cascade Mountains. Despite similar biomass of northern flying squirrels (Glaucomys sabrinus) (169 ± 13.9 g/ha) and deer mice (Peromyscus maniculatus) (160 ± 18.8 g/ha), flying squirrels dominated the breeding season diet based on both biomass (49%) and numbers (40%). Abundance of flying squirrels and western red-backed voles (Clethrionomys californicus) was more variable spatially ([Formula: see text]38% of process variation) than temporally (15%–24%), whereas abundance of deer mice was more similar across stands (12% spatial variation) than among years (68% temporal variation). Spotted owl reproductive success was statistically associated only with the abundance of deer mice (number of young per territory: r2 = 0.68). However, deer mice comprised only 1.6 ± 0.5% of the biomass consumed. The low temporal variability of the dominant prey species provided evidence that simple prey relationship models were not likely to explain the highly synchronous and temporally dynamic patterns of spotted owl reproductive performance. Reproductive success was likely a result of the interaction of both weather and prey and the life history strategy of this long-lived owl.

Habitat Selection by Northern Spotted Owls: The Consequences of Prey Selection and Distribution

We tested three predictions of a hypothesis that states Northern Spotted Owls (Strix occidentalis caurina) select habitat according to the distribution of their primary prey. Our predictions were that Northern Spotted Owls should (1) select larger (> 100 g) species among the assemblage of available prey, (2) select habitats according to the distribution of large prey, and (3) the owl's reproductive success should be influenced by the availability of large prey. We also evaluated the potential energetic value of several prey species. We found that Northern Spotted Owls (n = 11 pairs and 1 single male) in northwestern California differentially selected the dusky-footed woodrat (Neotoma fuscipes), a moderately large sigmodontine rodent (x mass = 232 g). When foraging, owls selected late seral forest edge sites where dusky-footed woodrats were more abundant. Although the relationship between site selection, prey abundance, and the owl's breeding success was not statistically significant, the average abundance of dusky-footed woodrats at sites foraged by breeding owls (x = 11.4 woodrats 100-trap-nights -1 ) was greater than at sites foraged by nonbreeding owls (x = 4.7 woodrats 100-trap-nights -1 ). We estimated that a male Spotted Owl would require 150,015 to 336,232 kJ over a 153-day period while helping to produce one young, and concluded that the selection of woodrats provided a potential energetic benefit over the use of other prey. These findings provide a partial explanation for the owl's affinity for late seral forests.

Diet and Nesting Success of Barn Owls Breeding in Western Nebraska

-We analyzed the diet of barn owls (Tyto alba) in Lincoln County, Nebraska during nesting seasons of 1984 through 1986 and their nest success in 1985 and 1986. Nesting attempts were made at 9 of 13 nest sites checked in 1985 and at 12 of 15 nest sites in 1986. Microtus ochrogaster comprised 32.7% of 10,140 prey items overall with marked increase in percent from 1985 to 1986. Barn own reproduction increased from 1985 to 1986 with more nests initiated, a higher proportion of successful nests and higher mean number of young fledged per nest attempt. Proportions of prey in the diet were significantly different from proportions of prey captured by trapping. Microtus ochrogaster was overrepresented and Peromyscus maniculatus underrepresented in the diet. Annual percentages of M. ochrogaster and Perognathus hispidus in the diet were negatively correlated with Reithrodontomys megalotis and with P. maniculatus but were not correlated with each other. Reithrodontomys megalotis and P. maniculatus were not correlated with each other. Reithrodontomys megalotis decreased and P. hispidus increased in the diet each year. A number of factors influence barn owl reproductive success including diet, quality of nest site and foraging ability of