Kestrel Nest Research Articles

Nest Box Cameras Provide Insight into Causes of Nest Failure for American Kestrels

ABSTRACT Although nest failure is a common occurrence in birds, oftentimes the causes, or details, of the failure are unknown because nests cannot be monitored closely or continuously. This inability to monitor nests in ways that allow for a detailed understanding of nest failure can hamper our ability to conserve declining species, such as the American Kestrel (Falco sparverius). Here we describe previously unreported observations from continuous video monitoring in kestrel nest boxes and biweekly nest monitoring via an extendable fiber optic endoscopic camera. From continuous video monitoring we observed adult kestrels consume a kestrel egg with little to no development and a European Starling (Sturnus vulgaris) pierce and remove an abandoned kestrel egg from a nest box. From biweekly monitoring with a fiber optic camera, we inferred that nest abandonment by kestrels was associated with eggs not developing either from infertility or early-stage embryo death. Although it is unclear how common such occurrences may be across the broader range of kestrels, these observations may provide impetus to explore these causes of nest failure more closely.

Second-breeding events of the common kestrel (Falco tinnunculus) in the Czech Republic

Abstract The laying of two clutches in a single breeding season can increase the fitness of the parent birds and stabilise a population. Our study analysed the rate of second-breeding attempts in the common kestrel (Falco tinnunculus) population in the Czech Republic. In the research, a total of 8,049 common kestrel nests were checked between 1979 and 2019. Of the 1,197 breeding events recorded during the study period in Moravia, 1,184 cases were first clutches and 13 cases (1.1%) were second breeding attempts. In Bohemia, a total of 6,852 breeding events were observed during the same study period, of which 6,811 were first clutches, 32 cases were late breeding attempts and 9 cases (0.1%) were second clutches. Second breeding events occurred only rarely, mainly during population outbreaks of prey species. During the mass outbreak of the common vole (Microtus arvalis) population in the Czech Republic in 2019, 5 (5.2%) of the 97 studied common kestrel pairs nested for the second time in Moravia; in Bohemia, second clutches were recorded in 3 (8.1%) of the 37 studied pairs. The second breeding attempts were recorded at an altitude of 272 ± 123 m (mean ± SD, range 179–560 m, n = 22) and commenced between 24 June and 25 July (29 June on average, n = 5). The range of the time gap between the first and the second clutch was 54 to 92 days (70.8 ± 16.3 days, n = 5). The second clutches consisted of an average of 4.1 ± 0.9 eggs (range 3–6, n = 12), with an average of 3.7 ± 0.9 fledglings in each successful breeding pair (range 2–5, n = 11) and 2.6 ± 1.9 fledglings for each initiated breeding attempt (range 0–5, n = 16).

Using drones to measure the status of cavity-nesting raptors

Many wildlife species, including hole-nesting raptors, occupy cavities that are challenging or unsafe for observers to examine. We conducted field tests using an inexpensive, off-the-shelf camera attached to an affordable commercial drone to assess the reproductive success of American kestrels ( Falco sparverius), a small, cavity-nesting raptor. Specifically, we developed a system that consisted of (1) a wireless mini camera transmitting images to an observer’s phone and (2) a Mini-Mavic 2 drone controlled through direct line-of-sight piloting. Following successful preliminary flights involving chicken eggs and other inanimate objects, we field-tested the system in two kestrel nest boxes in the wild. The system accurately recorded the contents of all nest boxes during the trials, provided the wind speed remained below approximately 2.5 m/s (5 knots). However, wind speeds at this level were observed only 40% of the days in our study area during kestrel breeding, which limited the surveying opportunities. Our system offers a promising method for surveying wildlife inhabiting inaccessible cavities.

Alleviating competition increases raptor breeding success: A case study of Jackdaws and Lesser Kestrels

Anthropogenic changes in the natural environment have led to the need to find alternative resources to ensure the persistence of biodiversity. In birds, nest sites can be a limiting resource in stenotopic populations. A method of active protection is the building of nest boxes. However, attractive nest sites attract target species and their competitors. From the species conservation point of view, our target species was the Lesser Kestrel (Falco naumanni), whose populations have recovered owing to the establishment of nest box colonies across Europe. However, they have been out-competed by Jackdaws (Corvus monedula) in recent years. Because corvids are intelligent and aggressive, we had to artificially control the competition from Jackdaws to allow Lesser Kestrels to nest. We aimed to discourage Jackdaws from taking over the studied colony and to ensure the continued breeding of Lesser Kestrels by manipulating access to the nest boxes. Data were collected during three breeding seasons in a Lesser Kestrel nest box colony using two manipulations in which we prevented Jackdaw occupation by closing some of the nest boxes and then gradually opening them. We found a significantly lower probability of Lesser Kestrels nesting and lower breeding performance in the control year than in the years in which access to the boxes was manipulated. The field experiment shows the high efficiency of manipulating the accessibility of nest boxes by closing and opening them at the right time in the context of their occupation by the target species and thus influencing their breeding performance.

American Kestrels Compete with European Starlings over Nest Boxes in Eastern Pennsylvania

ABSTRACT The American Kestrel (Falco sparverius) has been steadily declining throughout most of its eastern North American range, and the cause of this decline is still relatively unknown. As a cavity nesting species, the American Kestrel often competes with other cavity nesters such as the invasive and abundant European Starling (Sturnus vulgaris) over nest boxes. The relationship between European Starling presence at nesting sites and American Kestrel occupancy and nesting success is understudied. We analyzed data from nest boxes monitored in eastern Pennsylvania, USA, from 1992 to 2021 to identify changes in occupancy of American Kestrels and competitors, and to examine the relationship between competition at nest boxes and American Kestrel nesting parameters. We found that American Kestrel occupancy decreased while European Starling occupancy increased over the study period. All other species occupying nest boxes (small mammals, passerines, owls, and snakes) showed no significant occupancy trends. On average 21% of nest boxes remained unoccupied annually, and 7% of occupied nest boxes were used by both American Kestrels and competitors in the same breeding season. The presence of these competitors had negative associations with American Kestrel occupancy, clutch size, number of fledglings produced, and overall nesting success. Specifically, the rate of nesting success decreased by 26% when European Starlings used the same nest box within the same breeding season. In recent years, nesting productivity of American Kestrels has decreased, with the average number of nestlings, fledglings, and nesting success rate all declining, while the average clutch size remained constant. Our results suggest that American Kestrel nesting parameters in eastern Pennsylvania are negatively associated with competition for nest boxes during the breeding season. The opposing trends in occupancy for the European Starling and the American Kestrel in this study area coupled with the declining productivity of American Kestrel nests raise concerns over the future of this raptor species in eastern Pennsylvania.

Maximizing Nest Box Monitoring Effort to Detect American Kestrel Site Occupancy

ABSTRACT When designing nest monitoring protocols for raptors, investigators face a tradeoff between the desire to detect all nesting attempts and limited time and resources. American Kestrel (Falco sparverius) nest box occupancy (i.e., traditionally defined as number of nest boxes used divided by number of nest boxes available) is often the principal metric for tracking kestrel population size and trend. However, traditional nest box monitoring can lead to underestimates of local population size when kestrel pairs establish territories at nest boxes but are undetected because they do not lay eggs or their nests fail early in the nesting cycle. We analyzed empirical data collected during frequent visits (1–7 d intervals) to nest boxes throughout the breeding season (March–June during 2008–2014) in a dynamic occupancy modeling framework to assess the timing and intensity of monitoring needed to detect (with the same confidence level provided by frequent visits) the presence of kestrels on nest box sites in Florida. Modeled estimates of occupancy were similar to observed rates but trended slightly higher, especially in years with infrequent monitoring. Detection probability varied markedly over the duration of the breeding season; therefore, using a constant detection probability to determine the minimum number of visits needed to detect kestrel presence at a 95% confidence level produced misleading results. Modeling results indicated that >3 nest box inspections per season did not improve estimates of nest box occupancy. The common practice of monitoring American Kestrel nest boxes at approximately monthly intervals appears sufficient to detect the percentage of nest box sites (rather than nest boxes) used by kestrels, provided that monitoring visits are timed to straddle the peak period of egg laying. We recommend three nest box visits during the breeding season in Florida coincident with mid-March, mid-April, and mid-to-late May to maximize detection of kestrel nests. Investigators in other areas of the species' range will need to adjust the timing of our recommendations to local phenology. In addition, if accurately tracking local kestrel population size and trend is a project goal, then studies would benefit from using an occupancy approach rather than simply recording the percentage of nest boxes with nests, especially in years when fewer visits are possible.

Nest Boxes Increased Presence of American Kestrels in a Blueberry Production Region Despite Low Box Occupancy

ABSTRACT Landscape enhancements such as nest boxes can attract birds to agricultural areas, where they can provide ecosystem services such as pest reduction through their consumption of crop pests. However, there are large gaps in knowledge about how birds respond to enhancements. From 2014 to 2018 we installed American Kestrel (Falco sparverius; hereafter kestrel) nest boxes in a blueberry production region in western Michigan. From 2015 to 2018 we conducted surveys to monitor kestrel presence along 1.6-km transect segments (hereafter, sites) to estimate kestrel occupancy in areas with and without boxes. We also monitored box occupancy and reproductive success. Kestrel presence increased over time in the study area although there was some uncertainty in this trend. The presence of a box at a site did not increase kestrel presence there, but boxes in neighboring sites did increase presence. This indicated that enriching an area with boxes increases kestrel presence. Box occupancy rates were positively influenced by occupancy of the same box the previous year. Percent successful nests ranged from 75 to 100 percent, and mean number of fledglings produced was approximately 4 per nest box. Our results showed that nest boxes can serve as effective landscape enhancements to attract kestrels to agricultural landscapes, but the degree to which kestrels occupy boxes can vary geographically. Local-scale studies can provide information about the potential benefits and challenges of using nest boxes as a pest management tool.

Management of European Starlings in an American Kestrel Nest Box Program

ABSTRACT Artificial nest boxes have played an important role in American Kestrel (Falco sparverius) conservation worldwide, facilitating nesting and research efforts. However, these conservation efforts frequently unintentionally facilitate other cavity-nesting species including the European Starling (Sturnus vulgaris), a widespread invasive species in North America. Understanding how to deter European Starlings from occupying nest boxes is an essential responsibility of project design when deploying nest boxes. We examined the efficacy of five different abatement methods to mitigate the use of our nest boxes by European Starlings: nest removal, nest and egg removal, egg shaking, egg cracking, and egg oiling. We found spraying European Starling eggs with 100% food-grade corn oil and cracking eggs to be the most effective abatement methods. We recommend future American Kestrel nest box programs in this region use egg oiling or egg cracking on European Starling eggs.

Factors Associated with American Kestrel (Falco sparverius) Nest Box Occupancy and Reproductive Success in an Agricultural Landscape

ABSTRACT The American Kestrel (Falco sparverius), a small, cavity-nesting falcon that breeds across most of North America, is experiencing an apparent population decline across much of the United States that has yet to be sufficiently explained. With landscape change as a potential factor, the association of landscape composition with kestrel reproduction may assist not only in managing declines but also in improving the effectiveness and efficiency of nest box programs, which can bolster local populations and support monitoring and research efforts. We monitored 163 unique American Kestrel nest boxes over a 12-yr study period (2008–2019) in western Virginia to investigate the factors influencing kestrel reproductive success and we documented relatively high rates of both box occupancy (80%) and nest success (78.9%). In a study area dominated by both high- and low-intensity agriculture, we focused on identifying patterns in land cover composition that may limit reproductive success and associated each box with land cover composition metrics at four spatial scales. Generalized linear mixed models indicated nest boxes with a lower proportion of developed land within 500 m, and a higher proportion of crops and pasture/hay within 3 km were more likely to be occupied by kestrels. Although probability of kestrel nest success increased with reduced proportions of developed land within 100 m, the primary factors influencing success were clutch initiation date and the presence of European starlings (Sturnus vulgaris), with earlier nesting and the absence of starling activity resulting in higher nest success. Overall, cover-type associations with nest success and box occupancy were not strong and establishment of nest boxes in targeted kestrel habitat, while likely maximizing reproductive output, limits research opportunities to identify critical land cover thresholds for the species.

Food Habits of American Kestrels in the Southern High Plains of Texas

ABSTRACT The American Kestrel (Falco sparverius) is in general decline across its North American distribution. In contrast to widespread patterns of decline, kestrel populations appear stable in the southern Great Plains region. Historically, this region had a very low occurrence of kestrels, and their current abundance is highly likely due to vegetation and structures associated with settlement by people of European descent. To determine prey use by breeding kestrels, we placed motion-activated video cameras at preexisting kestrel nest boxes located in the Southern High Plains in 2017. We recorded over 4200 prey deliveries during 1748 hr of observation at five nests over the 4-wk brood-rearing period. On basis of frequency, these deliveries were dominated by reptiles (74.8%), with invertebrates (18.2%), mammals (4.4%), birds (2.9%), and unidentified (1.2%) prey used to lesser extents. Prey delivery rates were high relative to other studies; across the brood-rearing period we recorded an average of 2.3 deliveries/hr, equating to an average of 0.49 deliveries and 3.85 g of prey/nestling/hr. Because invertebrates dominate the diet reported in most kestrel food habit studies, the volume of reptiles captured as prey was unexpected. Even more unanticipated was the number of large prey captured, including juvenile eastern cottontails (Sylvilagus floridanus) and ground squirrels (Ictidomys tridecemlineatus, Xerospermophilus spilosoma). We suspect the proportion of vertebrate prey captured during the nesting season may explain the local high rates of nesting success and number of young fledged.

Brood sex ratio modulates the effects of extra food on parental effort and sibling competition in a sexually dimorphic raptor

Conflicts are inherent to family systems and may occur at three levels. First, each parent benefits if its mate takes the greater share of parental investment. Second, offspring try to manipulate their parents into devolving more resources than it is optimal for them. Third, siblings compete for resources. Food availability can affect the dynamics of each level of interaction. By means of a food supplementation experiment, we assessed how the initial availability of extra food during breeding affects later parental effort, sibling competition, and parent-offspring interactions in a small dimorphic raptor, the lesser kestrel (Falco naumanni). Being the larger sex, female nestlings are likely to have higher energy requirements. Female-biased broods had a higher rate of aggressive interactions and were fed more frequently in control nests. Food was not shared evenly among broodmates, and daughters tended to receive more feedings than sons. In young broods, parents controlled food allocation by entering the nest, whereas in older broods, offspring controlled food allocation by monopolizing the nest site entrance. Extra food induced male parents to reduce the rate of feedings delivered by entering the nest. Additionally, extra food improved nestling growth in male-biased broods, leading to an increase in the frequency of parental feedings and aggressive interactions, likely due to faster growth rates. These findings reveal a key effect of brood sex ratio in determining family interactions in a species with reverse sexual size dimorphism and suggest that all levels of conflict between family members should be considered simultaneously when investigating the evolution of parental care. Breeding poses energetic costs on parents, and environmental resources are usually limited. To successfully breed, parents coordinate their efforts and manage the allocation of resources to offspring, while offspring communicate their needs. Conflict can arise among family members: each parent benefits if the other takes on most of the workload, offspring ask for more care than what parents can provide, and siblings compete for food. Food availability affects these interaction levels separately, but they have rarely been integrated. By providing extra food to lesser kestrel (Falco naumanni) nests, we show that parental provisioning behaviour and sibling competition are simultaneously affected by initial resource availability during breeding. Although lesser kestrel nestlings show only moderate sex differences in body size (and therefore energy requirements), the effect of extra food on family interactions primarily depended on the sex ratio of the brood.

Supernormal clutches of American Kestrels (Falco sparverius) in peninsular Florida

The clutch size of the American Kestrel (Falco sparverius) has been well studied across a range of latitudes and habitats and typically is 4 or 5 eggs. Neither polygyny nor brood parasitism has been reported for the species. I report here 3 instances of supernormal clutches, of 8 or 9 eggs, documented in kestrel nest boxes in north-central Florida and discuss 4 possible explanations for these observations. In 2 nests only 1 egg hatched, and in 1 nest none of the eggs hatched. Although I was unable to make a conclusive finding about the cause for supernormal clutches, it is likely that they were laid by more than 1 female, either cooperatively or non-cooperatively.

Effects of Nest Box Installation on a Distribution Power Line: Increased Eurasian Kestrel Nesting, Reduced Electrocutions, and Reduced Electrical Faults

Electrical pylons are frequently used by birds for perching, roosting, and nesting. These behaviors can lead to electrocutions, particularly when pylons are constructed of grounded concrete and steel crossarms, as they were in our study area near Arak, Iran. To address electrocutions of Eurasian Kestrels (Falco tinnunculus) and a variety of passerines nesting on a 20-kV distribution line, we documented construction and use of nests on pylons on a 34-km segment of power line in 2018. Following removal of nests by the electric utility operating the line, we installed nest boxes on pylons that previously supported nests, and in 2019 we documented use of those nest boxes. We predicted that after installation of nest boxes, numbers of Eurasian Kestrel nests would increase, and numbers of nests outside of nest boxes, avian electrocutions, and faults (electric current arcing from conductors to pylons) would decrease. All four predictions were validated. We documented 31 nests in 2018, including 3 Eurasian Kestrel nests. In 2019, we documented 6 nests outside of nest boxes, and 31 nests in nest boxes, including 16 Eurasian Kestrel nests. In 2018, we found 1 electrocuted Eurasian Kestrel, and 39 electrocuted passerines. In 2019, we found 3 electrocuted Eurasian Kestrels, 11 passerines, 2 Eurasian Eagle-Owls (Bubo bubo), and 1 Steppe Eagle (Aquila nipalensis). The rate of electrocutions per nest for Eurasian Kestrels decreased from 0.33 to 0.19, and the electrocution count for all birds decreased by 57.5%. Electrical faults, an indirect measure of potential avian electrocutions, decreased from 173 in 2018 to 120 in 2019. Although there is some risk that nest boxes on power poles could create ecological traps, our results suggest that in this study electrocutions and electrical faults were reduced, supporting conservation goals and electric power reliability goals while simultaneously reducing electric utilities' maintenance obligations.

Nest Box Entrance Hole Size Influences Prey Delivery Success by American Kestrels

Nest boxes are a popular tool for research and conservation of American Kestrels (Falco sparverius; hereafter “kestrel”). The size of nest box entrance holes affects occupancy, interspecific competition, and nest predation for a number of bird species, but effects on prey delivery success are unstudied. We used digital video cameras to monitor kestrels using two nest box designs, one with a small circular entrance hole (8.75 cm in diameter; n = 8) and the other with a large U-shaped entrance hole (7.62 cm wide by 12.07 cm high; n = 6), to compare the rates at which kestrels failed to deliver large prey (vertebrates) into the nest box while provisioning nestlings. Across 111 d of monitoring, we observed a significantly higher prey delivery failure rate at the boxes with small holes (8.9%) compared to boxes with large holes (1.6%). Boxes with small holes fledged 4.33 nestlings and boxes with large holes fledged 4.5. These results suggest that kestrels nesting in boxes with small entrance holes may have higher costs while provisioning nestlings, compared to kestrels using boxes with larger entrance holes. We conclude that the ideal entrance hole size for kestrel nest boxes may be a compromise between being small enough to minimize predation, yet large enough to allow kestrels with large prey to easily enter. Future research should investigate whether boxes with higher prey delivery failure rates have lower reproductive success.

Kestrel nest box occupancy and fledging rates and the effect of kestrel presence and absence on bird abundance and activity in fruiting crops in the Niagara Region and Norfolk County

Frugivory by birds has been well documented and can have significant economic impacts globally. Invasive or pest species such as European starlings (Sturnus vulgaris) and American robins (Turdus migratorius) have been most frequently implicated and are omnivorous, adaptable, and opportunistic. Reducing their impact on ripening fruit crops is a constant topic of research in crop protection. Often, deterrents are installed at time of ripening but are unsuccessful if overused, as their continued presence at a single location allows for habituation by frugivorous species. American kestrels (Falco sparverius) are currently in decline in Southern Ontario. Habitat fragmentation, urbanization, climate change and invasive species have all contributed to this phenomenon. Kestrels, being cavity nesting birds, can be attracted to nest or roost in areas by installing kestrel nest boxes. Although not present during the ripening period of the fruiting crops studied, kestrels significantly reduced overall bird activity and abundance, and the abundance of thrush species (American robins) during their use of nest boxes in sensitive crops in the Niagara Region, while also promoting the continued presence of an at-risk species. Facilitating the presence of kestrels using nest boxes, or promoting the presence of birds of prey in general, can therefore be an effective bird deterrent mechanism. However, competition for the use of nest boxes from invasive species such European starlings decreased the successful occupancy rate of installed nest boxes by either kestrels or other beneficial species. Therefore, the monitoring, management, and maintenance of installed boxes is integral to their success as a deterrent mechanism and should be considered before their installation.

Effect of supplemental feeding on nesting success in the Lesser Kestrel (Falco naumanni)

The effect of food supplement to Lesser Kestrel (Falco naumanni) nests during the nestling period (from hatching to fledging) was studied in two nesting colonies in Israel – Alona and Jerusalem. Our hypothesis, based on diminishing returns considerations, was that food supplement will have a greater effect on fledgling success in the food-limited, urban colony of Jerusalem, than in the rural colony of Alona. Indeed, food supplement had a significantly positive effect on breeding success in both colonies. However, and contrary to our prediction, the decrease in chick mortality between supplemented and control nests in Jerusalem was not larger than in Alona (actually it was numerically smaller, albeit not significantly so). This implies either that additional factors, possibly urbanization associated, other than food limitation, might be responsible for the difference in nesting success of Lesser Kestrels between Alona and Jerusalem, and/or that the amount or the nutritional quality of the additional food provided to supplemented nests (three mice per chick per week), was not enough.

Diversionary feeding as a means of reducing raptor predation at seabird breeding colonies

Predation can limit bird populations, especially in ground-nesting and colonial species. Solutions are usually available to reduce the impacts of predation if the predator is non-native or not legally protected (e.g. predator control or exclusion). However, when the predator is protected by law (e.g. raptors) potential solutions are limited. If predator and prey are both species of conservation concern this can bring the conservation of these species into conflict. Diversionary feeding (DF) is a potential solution, whereby predators are provided with food to reduce their motivation to hunt. The efficacy of DF has rarely been tested thus, in this paper, we test the efficacy of DF to reduce predation by kestrels, Falco tinninculus, a protected and declining raptor, on little tern chicks, Sternula albifrons, a protected seabird, within an internationally important colony in eastern England. We used a 17-year dataset of annual estimates of little tern productivity and counts of kestrel predation events to compare years with and without DF (DF = 6 years). During a four-year period of more intensive monitoring efforts, where we employed DF at focal kestrel nests in alternate years, we quantified the rates of kestrel predation at the colony and prey provisioning rates at kestrel nests. Predation rates were 47% lower and productivity of little terns doubled in years when kestrels were fed. Intensive monitoring showed that predation rates by kestrels at the colony were 88% lower in the two years when kestrels were fed. Provisioning rates of all wild prey and little tern prey, was 3.4 and 6.2 times lower in DF years and the likelihood of little tern chicks being provisioned at nests was lower when alternative wild prey were provisioned. DF is an effective tool to reduce predation and increase productivity of little tern colonies threatened by kestrel predation. The magnitude of these effects on little tern productivity was sufficient to promote population increases. Raptor conservation has resulted in increasing populations of many species and it is expected that predator-prey conflicts are likely to increase. DF could be an important tool to manage these conservation issues, but further tests of the efficacy in different predator-prey systems will be needed.

Webcams as an untapped opportunity to conduct citizen science: Six years of the American Kestrel Partnership's KestrelCam

Hundreds of zoo-based or wildlife webcams have become available during the past twenty years, mostly with the goal of educating the public. However, there has been virtually no peer-reviewed research that evaluates the education, conservation, or scientific impact of webcams. Here, we provide one of the few examples of a webcam used for citizen science, and the only test of efficacy for crowd-sourced data collection using webcams. The Peregrine Fund streamed six seasons of American Kestrel (Falco sparverius) nests using the same nest box from 2012 through 2017 and viewers input observations into an online portal. We analyze trends in participant and kestrel behavior and test for sources of bias in this citizen scientist-generated dataset by independently reviewing a subset of recordings to determine accuracy of viewer-logged data. Citizen scientists logged a maximum of approximately 5.25% of all footage, but with an accuracy of 88%. Although number of participants declined yearly, on average, participants became more engaged. Sources of bias were related to people's daily activity periods (i.e., less participation at night) and activity within the nest box (i.e., less participation when there were no birds in the box). This citizen scientist-generated dataset generally corroborated the literature regarding American Kestrel biology. Researchers may be cautiously optimistic that datasets generated by citizen scientists can provide valuable information on a given system or study species. Given the ubiquity of webcams and their potential competition for conservation dollars, more research evaluating any aspect of their impact or application is sorely needed.

Effects of American Kestrel Nest Boxes on Small Mammal Prey in Cherry Orchards

In order to potentially reduce use of environmentally damaging rodenticides, integrated Pest Management (IPM) for rodents, or Ecologically Based Rodent Management (EBRM), proposes a more sustainable management approach using strategies informed by an increased understanding of rodent population and community ecology, including interactions with important predators, such as raptors. Nest boxes and perches can encourage raptor presence in agricultural areas and potentially enhance the regulatory ecosystem services provided by raptor predation of agricultural pests. To assess this idea, we studied American kestrels (widespread, generalist predators that readily use nest boxes) in a fruit-growing region of northwestern Michigan. The most common mammal prey in the diets of these kestrels from 2013 through 2016 were voles, which are considered the most important rodent pests in temperate fruit orchards. We utilized live trapping to measure small mammal abundances and activity during the summer at sites with and without active kestrel nest boxes; furthermore, we utilized camera trapping to measure small mammal presence during the winter, when damage to trees is most likely. As predicted, small mammal abundance and activity was lower at orchards with active kestrel boxes and at orchards that had been more recently mowed; however, these differences did not carry over as differences in winter presence in orchards. Our sampling demonstrated that voles were absent from orchards during both summer and winter, which suggests that orchards offer insufficient cover except under certain conditions, such as sustained snow cover. Instead, mice were the most abundant small mammals in most orchards during the summer and were also present during the winter. More evidence is therefore needed to determine the extent of orchard damage attributable to Peromyscus spp. and whether indirect effects of kestrels on Peromyscus spp. may reduce damage. We provide recommendations for future research on the effects of raptor predation in orchards.

Factors affecting the spatial distribution and breeding habitat of an insular cliff-nesting raptor community.

The specific spatial distribution and habitat association—strongly influenced by environmental factors or competitive interactions—are major issues in ecology and conservation. We located and georeferenced nesting sites of five cliff-nesting raptors (Egyptian vulture Neophron percnopterus [a locally extinct species], common buzzard Buteo buteo, osprey Pandion haliaetus, common kestrel Falco tinnunculus, Barbary falcon Falco peregrinus pelegrinoides), and common raven Corvus corax on one of the most biodiverse hotspot within the Canary Islands (Teno, Tenerife). We used generalized linear models to evaluate the factors affecting abundance, richness, and intra- and interspecific interactions. Raptor abundance increased with slope, shrub-covered area, and habitat diversity, and decreased with altitude, and forested and grassed areas. Richness increased with slope and decreased with altitude. Threatened species (osprey, Barbary falcon, and raven) occupied cliffs farther away from houses and roads, and more rugged areas than the non-threatened species. The models suggested that the probability of cliff occupation by buzzards, falcons, and ravens depended only on inter-specific interactions. Buzzard occupation increased with the distance to the nearest raven and kestrel nests, whereas falcons and ravens seek proximity to each other. Teno holds between 75% and 100% of the insular breeding populations of the most endangered species (osprey and raven), indicating the high conservation value of this area. Our study suggests that the preservation of rugged terrains and areas of low human pressure are key factors for raptor conservation and provide basic knowledge on the community structure and habitat associations to develop appropriated management actions for these fragile island populations.