American Kestrels Falco Sparverius Research Articles

Disentangling relationships between physiology, morphology, diet, and gut microbial diversity in American kestrel nestlings

Gut microbiota are increasingly recognized as important drivers of host health and fitness across vertebrate taxa. Given that gut microbial composition is directly influenced by the environment, gut microbiota may also serve as an eco‐physiological mechanism connecting host ecology, such as diet, and physiology. Although gut microbiota have been well‐studied in mammalian systems, little is known about how gut microbial diversity and composition impact morphological and physiological development in wild birds. Here, we characterized both diet and gut microbial diversity of free‐living American kestrel Falco sparverius nestlings throughout development to test whether gut microbial diversity predicts host morphological and physiological traits in either contemporary or time‐lagged manners. Gut microbial alpha diversity on day 21 of nestling development was positively correlated with diet alpha diversity representative of the majority of nestling development (days 5–20). Gut microbial alpha diversity early in development was negatively correlated with body mass in both contemporary and time‐lagged manners. Gut microbial alpha diversity early in development was positively correlated with blood glucose later in development. As nestlings experience rapid growth demands in preparation to fledge, these time‐lagged associations may indicate that gut microbial diversity at early critical developmental windows may determine the future trajectory of morphological and physiological traits underlying metabolism that ultimately impact fitness.

Coding-Complete Genome Sequence of a Falcon aviadenovirus A Strain Associated with Necrotizing Hepatitis in an American Kestrel ( Falco sparverius )

ABSTRACTA necropsy was performed on an American kestrel (Falco sparverius) with necrotizing hepatitis associated with inclusion bodies, suggesting an adenovirus infection. A next-generation sequencing assay was conducted on the liver, and the coding-complete genome sequence of a Falcon aviadenovirus A strain was revealed.

Diet Variation of a Generalist Predator, the American Kestrel Falco sparverius, in a Gradient of Agricultural Intensification in Central Argentina

Agricultural expansion at the expense of natural habitats and the intensification processes in agricultural production are globally among the main causes of biodiversity and ecosystem services loss at large scale. This process can completely alter food provision for birds and have negative consequences for their diet and breeding performance. Under the hypothesis that changes in land use limit food resources for raptors, our aim was to analyze variation in nestling diet between natural areas and areas with different degrees of agricultural intensification (natural forest, traditional farmland, intensive farmland) in a population of American Kestrel Falco sparverius breeding in nest boxes and cavities. Through the analysis of pellets and prey remains collected during the reproductive season of 2012–2013 we found no differences in diet diversity among areas and the diet in the three areas was monopolized by arthropods. However, the diet did change in composition between areas. Numerically, Orthoptera dominated the diet in the three areas, although with a higher percentage in the forest area. The frequency of vertebrate consumption was affected positively by the area occupied by natural forest and stubble, while the soybean cover affected the consumption in a negative way. In both agricultural areas, the diet was complemented with different groups of arthropods suggesting that changes in land use generate a functional response in the American Kestrel that is able to take advantage of available resources in each sampling area. Long-term analysis of diet variation within the framework of agricultural intensification and its relation with demographic parameters and individual performance will allow to evaluate the impact of this variation in the diet on kestrels.

Intra‐specific variation in migration phenology of American Kestrels (Falco sparverius) in response to spring temperatures

In migratory birds, among‐ and within‐species heterogeneity in response to climate change may be attributed to differences in migration distance and environmental cues that affect timing of arrival at breeding grounds. We used eBird observations and a within‐species comparative approach to examine whether migration distance (with latitude as a proxy) and weather predictors can explain spring arrival dates at the breeding site in a raptor species with a widespread distribution and diverse migration strategies, the American Kestrel Falco sparverius. We found an interactive effect between latitude and spring minimum temperatures on arrival dates, whereby at lower latitudes (short‐distance migrants) American Kestrels arrived earlier in warmer springs and later in colder springs, but American Kestrels at higher latitudes (long‐distance migrants) showed no association between arrival time and spring temperatures. Increased snow cover delayed arrival at all latitudes. Our results support the hypothesis that short‐distance migrants are better able to respond to conditions on the breeding ground than are long‐distance migrants, suggesting that long‐distance migrants may be more vulnerable to shifts in spring conditions that could lead to phenological mismatch between peak resources and nesting.

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.

Yearly temperature fluctuations and survey speed influence road counts of wintering raptors

Globally, evaluation of population trends is the most pressing research need for many species of conservation concern. Road counts for birds of prey are useful for monitoring long‐term population trends and examining year‐to‐year variations in abundance. We examined data from 2155 road surveys conducted from 2001 to 2018 by community scientists who recorded > 85 000 individuals of 14 species of raptors while participating in the Pennsylvania Winter Raptor Survey, in Pennsylvania, USA. We estimated abundance and population growth rates while accounting for observation error by using dynamic Bayesian state‐space models. Model estimates indicated that counts of wintering Bald Eagles Haliaeetus leucocephalus, Red‐shouldered Hawks Buteo lineatus and Black Vulture Coragyps atratus increased over the course of the study. Counts of Rough‐legged Buzzard Buteo lagopus, Red‐tailed Hawk Buteo jamaicensis, Northern Harrier Circus hudsonius, Turkey Vulture Cathartes aura and American Kestrel Falco sparverius varied more (CV > 5.0) over the duration of the study than other species did. Higher winter temperatures were associated with increases in counts of species whose local populations are partially migratory (American Kestrel and Red‐tailed Hawk), and with lower counts of a long‐distance arctic migrant – Rough‐legged Buzzard. Counts of these species were therefore correlated such that more American Kestrels and Red‐tailed Hawks were counted during years when Rough‐legged Buzzards were less frequently seen. Generally, the number of individuals counted declined as survey speed increased. A general rule for road counts therefore seems to be ‘slower is better’, consistent with past recommendations that observers travel at a speed < 40 km/h during road counts. Our study highlights the utility of road surveys and advances analytical approaches to monitor raptors.

Demography of a widespread raptor across disparate regions

Demographic differences between stable and declining populations can lend insight into drivers of population decline. The American Kestrel Falco sparverius is a widespread and often‐studied falcon, yet its demography is poorly understood, and the causes of observed population declines across much of North America remain unknown. Using integrated population models and sensitivity analysis, we examine how vital rates drive growth in population levels of American Kestrels at four discrete study sites – Florida, Idaho and Pennsylvania with stable nestbox occupancy, and New Jersey, where occupancy is declining. Population growth was most sensitive to changes in adult survival, yet was most correlated with immigration, in all populations. Additionally, population growth was positively correlated with survival rates of juveniles in Pennsylvania. We found evidence for density‐dependence in at least one vital rate for all populations except Florida. Fecundity was density‐dependent in New Jersey and Idaho, and the population growth rate was density‐dependent in Idaho. Adult survival, immigration and the population growth rate were density‐dependent in Pennsylvania. The New Jersey population had the highest rate of fecundity, suggesting that declines there are probably not caused by reproductive failure. Our study demonstrates that two principal demographic processes, adult survival and immigration, drive population dynamics of American Kestrels – both of which are understudied.

Trophic segregation of the Burrowing Owl and the American Kestrel in fragmented desert in Mexico

ABSTRACT We analysed the diet of the Burrowing Owl (Athene cunicularia) and the American Kestrel (Falco sparverius) in a fragmented habitat and natural surroundings in the arid ecosystem of the Baja California peninsula, Mexico. Both small-sized raptors are considered in the same trophic guild, and as keystone species, interactions between them could be of interest for wildlife management in fragmented landscapes for agricultural activities. The diet analysis of these top predators could be a good monitor of prey abundance, some of which may be considered detrimental for agricultural activities. Prey frequencies in owl pellets were higher for arthropods (53.1%) and rodents (32.4%), but rodents were the most abundant item in terms of biomass (34.5%). Arthropods also showed higher relative frequencies in kestrel pellets (36.4%), but reptiles were the second in order of importance (28.4%) and contributed the most (64.7%) to the total prey biomass. The biomass contribution (66.1%) of vertebrates in the diet of the Burrowing Owl was lower than for the American Kestrel (95.6%) in a fragmented habitat area. Most prey types were present in the diet of both raptors, but we found significant differences in the biomass contributions of each category. Reptiles and rodents were the prey items that contributed most to the differences in the raptors’ diets, in terms of biomass (33% and 20.3%, respectively). Close nesting surroundings (0.5 km and 1 km radius) evidenced a higher proportion of natural vegetation in the kestrel’s (50.6% and 38.9%, respectively) than in owl’s potential home range (25.8% and 16.4%). The differences in diet suggest some degree of niche partitioning of these species likely due to the more flexible owl’s nesting habitat requirements and to the extended nocturnal activity of the species. These results reflect the capability of being complementary species, both exploiting some pests that are harmful for agriculture, and evidencing the importance of both species as regulators of agro-ecosystems in the peninsula of Baja California.

American Kestrel Responses to Aircraft in an Airport Environment

Animal perception of risk and response to vehicle approach affect survival. We quantified American Kestrel (Falco sparverius) behavioral response to aircraft approach in an airport environment, by examining the likelihood of initiating escape, flight-initiation distance (FID), and the type of escape response. We observed 32 American Kestrel-aircraft interactions at Burke Lakefront Airport in Cleveland, Ohio, USA, from June 2015 through September 2016. American Kestrels responded to aircraft by initiating escape (i.e., FID > 0) 34% of the time, with a mean FID of 64 m and frequent (82%) returns to the same location occupied before the escape. Based on effect size estimates, the trajectory of an aircraft approach (direct vs. nondirect) was a more important determinant of whether an American Kestrel initiated escape than was the type of aircraft (propeller or piston vs. jet-powered). Assuming an average aircraft ground speed of 51.4 m/sec on landing phase, birds responded on average 1.2 sec before an aircraft was over or at the bird's position. Based on the relationship among likelihood of initiating escape, FID, and reported bird-aircraft collisions (strikes) across species studied at the same airport, American Kestrels followed a strategy of relatively low likelihood of initiating escape and short FIDs, which led to infrequent strikes. However, compared to American Kestrels, some other species that followed a similar strategy had more aircraft strikes, whereas some species with different strategies experienced similar numbers of strikes. This variation among species in escape strategies and strikes should be studied further, as it could lead to new ways of modeling bird-strike risk at airports.

Effects of biosolids amendments on American Kestrel (Falco sparverius) nest-site selection and diet

Fertilization is a common practice, as it improves plant yields. In many areas, biosolids (remains from treated wastewater) are used instead of chemical fertilizers owing to multi-year nutrient release and positive changes in soils and water retention. Little is known about whether biosolids affect animal consumers. Here, we examine diets and nesting sites of American Kestrels (Falco sparverius Linnaeus, 1758) in British Columbia, Canada. Our major study area was a large cattle ranch that has been grazed for over a century and where biosolids were applied in the previous 1–3 years. Kestrels selected nests in areas with higher Northern Flicker (Colaptes auratus (Linnaeus, 1758)) nest density and with a higher proportion of pastures with biosolids applications, but with less forest. Kestrels were observed more often on biosolids-amended pastures than in untreated areas. Kestrels primarily ate voles (genus Microtus Schrank, 1798), but also consumed grasshoppers (Orthoptera) late in the breeding season when grasshoppers were abundant. Kestrel diets were slightly more varied on a nearby control area than on the ranch. Our results suggest that biosolids applications improve prey availability for Kestrels, thus potentially acting as a restoration tool in areas with degraded habitats or where Kestrels have declined.

Survival, Site Fidelity, and Territory Size of American Kestrels Wintering in an Agricultural Landscape of South Texas

American Kestrels (Falco sparverius) are North America's most abundant falcon, but they are declining throughout much of their range. Studies of nesting success are common, but far less is known about kestrels during migration and on the wintering grounds. We studied kestrels wintering along county roadways in South Texas. We trapped and color-marked 65 kestrels during October through December in 2014 and 2015 and searched for marked individuals once per week using a spotting scope, until birds started departing from the wintering grounds. We also searched for returning kestrels from September to March, 2015–2016 and 2016–2017. We used the Cormack–Jolly–Seber (CJS) models in Program MARK to estimate apparent survival, and we estimated two metrics of site fidelity as well as a spatial metric of site fidelity. We estimated territory size for individuals with ≥10 locations using the maximum linear distance between locations. We estimated winter survival (20 wk) as 67.1 ± 7.1% for kestrels in the winter they were marked and 84.4 ± 6.3% for returning birds. The 2-yr average apparent winter site fidelity was 27.8% for males and 50.2% for females, and the 2-yr average adjusted winter site fidelity was 41.7% for males and 65.7% for females. Linear average territory size ranged from 539 ± 34 m in Winter 3 to 738 ± 74 m in Winter 1. Our estimates of site fidelity are 12–15% greater than previously reported, and our linear winter territory sizes (pooled over 3 yr) were less than half the size of those previously reported for wintering American Kestrels. Small territories and high winter site fidelity suggest that South Texas agricultural areas are likely an important region for wintering kestrels.

Possible Functions of Tail-Pumping by American Kestrels (Falco Sparverius)

When perched, several species of small falcons, including American Kestrels (Falco sparverius), often pump their tails, but the possible function of this behaviour is unknown. Our objective was to use observations and experiments to examine the possible function(s) of tail-pumping by American Kestrels. Fieldwork was conducted from March 2015 to December 2015 at the Blue Grass Army Depot in Madison County, Kentucky. During observations of focal kestrels, we noted their behaviour (e.g. landing on a perch, hunting, or consuming prey), including when and how often they pumped their tails (i.e. rapid movement of the tail down, then back up to its original position). Kestrels typically tail-pumped when landing on a perch (mean = 4.1±0.2 pumps per 10 s) and consuming prey (mean = 2.4±0.2 pumps per 10 s). When hunting, kestrels tail-pumped at higher rates during the 30 s prior to attacking (mean = 1.1±0.3 pumps) than they did during the 30–60 s interval before an attack (mean = 0.3±0.1 pumps). During experiments where kestrels were presented with models of a conspecific and a predator (Cooper's Hawk, Accipiter cooperi), we found no difference in rates of tail-pumping prior to and during the presentation. These results suggest that tail-pumping by American Kestrels is not used either to communicate with conspecifics or as a predator-deterrent signal. Rather, kestrels appear to tail-pump to help maintain balance on perches when landing and consuming prey. In addition, prior to attacking prey, kestrels typically bob their heads (possibly to aid in judging distances), and tail-pumping may help them maintain stability as they head-bob and prepare to attack.

Monk Parakeets Provide Nesting Opportunities for the Threatened Southeastern American Kestrel

We report on the nesting of Southeastern American Kestrels (Falco sparverius paulus) in nonnative Monk Parakeet (Myiopsitta monachus) nests in Florida, USA. Two kestrel pairs nested within parakeet stick nests located on top of steel support structures at electric utility substations in Pasco County, Florida. Kestrels fledged young at both sites. The Monk Parakeet's ability to exploit anthropogenic habitats may facilitate the use of these areas by nest-site-limited species such as the Southeastern American Kestrel.

Commentary: Research Recommendations for Understanding the Decline of American Kestrels (Falco sparverius) Across Much of North America

Resumen La naturaleza carismatica y la enigmatica disminucion poblacional de Falco sparverius ha provocado el interes y la preocupacion tanto de cientificos (ciudadanos y profesionales) como del publico en general. Aunque se han propuesto diversas razones como causas de esta disminucion, hay poca o nula evidencia empirica para la mayoria de las amenazas hipotetizadas y consecuentemente no existen recomendaciones de gestion apoyadas en evidencia empirica. Presentamos recomendaciones para investigaciones futuras sobre la causa de la disminucion poblacional de F. sparverius. Ademas, sugerimos prioridades para monitorear e identificar los condicionantes de las tasas de supervivencia y reproduccion a traves de modelos demograficos. Investigaciones sobre la fenologia, la conectividad migratoria y el uso de cavidades naturales como nidos mejorarian el seguimiento de F. sparverius y nuestra comprension sobre los declives poblacionales, mientras que estudios demograficos durante el ciclo anual completo de F. sparv...

Relative Abundance, Habitat Use, and Seasonal Variability of Raptor Assemblages In the Flooding Pampas of Argentina

Abstract We evaluated the species composition, relative abundance, habitat use, and seasonal variability of raptor assemblages in the Flooding Pampas of Argentina, which represents the southeastern part of the biome known as the Rio de la Plata Grasslands. We conducted seasonal roadside surveys to detect raptors in modified and natural habitats over a 3-yr period from spring 2006 through autumn 2009. We classified raptor species according to their relative abundances and occurrence frequencies, and compared the assemblage composition among land-cover types (croplands, grazing fields, periurban areas, and grasslands) and seasons. The raptor assemblage in the Flooding Pampas comprised 16 species, representing approximately 43% of all raptor species in the biome. The Chimango Caracara (Milvago chimango) was the dominant species in all land-cover types and seasons. The Southern Caracara (Caracara plancus), American Kestrel (Falco sparverius), and Roadside Hawk (Rupornis magnirostris) were all abundant and ver...

Raptor and large soaring bird migration across the Isthmus of Tehuantepec, Mexico: distribution, seasonality, and phenology

SummaryWe present the first study of the spatial and temporal dynamics of raptors and large soaring birds from the Isthmus of Tehuantepec, Mexico. Using systematic migration counts from multiple localities in the southern states of Oaxaca and Chiapas, as well as observations of their flight trajectories during eight consecutive years (2007–2014), we describe the magnitude of these movements, their geographic extent, and the phenology of the most abundant species in both spring and fall seasons. The most abundant species were Turkey VultureCathartes aura, Swainson’s HawkButeo swainsoni, Broad-winged HawkButeo platypterus, Wood StorkMycteria americana, American White PelicanPelecanus erythrothynchos, Franklin’s GullLeucophaeus pipixcan, and American KestrelFalco sparverius. In spring, the seasonal average magnitude of migration was over 28,000 birds, while in autumn the average was over one million. The aggregated seasonal phenologies recorded illustrate a variety of migration patterns. The inter-annual variation is lower in autumn than in spring. Migrating raptors and other soaring birds did not seem to use any topographical feature as a leading line for their movements in spring, while in autumn they did. We estimated the main axis of spring flights to run along a SE–NW vector, while autumn migration follows a WNW–ESE general trajectory. Our results place the isthmus as one of the five most important sites in the world for raptors and soaring migrants. Sustaining annual migration counts at these sites is of high importance to track substantial portions (> 90%) of the global population of Turkey Vulture and Swainson’s Hawk, as well as over 10% of the global population of Broad-winged Hawk. Autumn migration counts have the potential for long-term population monitoring.

Ground Squirrel Shooting and Potential Lead Exposure in Breeding Avian Scavengers.

Recreational ground squirrel shooting is a popular activity throughout the western United States and serves as a tool for managing ground squirrel populations in agricultural regions. Belding’s ground squirrels (Spermophilus beldingi) are routinely shot in California, Nevada, and Oregon across habitats that overlap with breeding avian scavengers. Ground squirrels shot with lead (Pb)-based bullets may pose a risk to avian scavengers if they consume carcasses containing Pb fragments. To assess the potential risk to breeding avian scavengers we developed a model to estimate the number, mass, and distribution of Pb fragments in shot ground squirrels using radiographic images. Eighty percent of shot carcasses contained detectible Pb fragments with an average of 38.6 mg of Pb fragments. Seven percent of all carcasses contained Pb fragment masses exceeding a lethal dose for a model raptor nestling (e.g. American kestrel Falco sparverius). Bullet type did not influence the number of fragments in shot ground squirrels, but did influence the mass of fragments retained. Belding’s ground squirrels shot with .17 Super Mag and unknown ammunition types contained over 28 and 17 times more mass of Pb fragments than those shot with .22 solid and .22 hollow point bullets, respectively. Ground squirrel body mass was positively correlated with both the number and mass of Pb fragments in carcasses, increasing on average by 76% and 56% respectively across the range of carcass masses. Although the mass of Pb retained in ground squirrel carcasses was small relative to the original bullet mass, avian scavenger nestlings that frequently consume shot ground squirrels may be at risk for Pb-induced effects (e.g., physiology, growth, or survival). Using modeling efforts we found that if nestling golden eagles (Aquila chrysaetos), red-tailed hawks (Buteo jamaicensis), and Swainson’s hawks (B. swainsoni) consumed shot ground squirrels proportionately to the nestling’s mass, energy needs, and diet, 100% of the nestling period would exceed a 50% reduction in delta-aminolevulinic acid dehydratase production threshold, the last 13–27% of the nestling stage would exceed a reduced growth rate threshold, but no nestlings would be expected to exceed a level of Pb ingestion that would be lethal.

Gregarious Winter Roosting and Early Morning Perching Behavior of American Kestrels (Falco sparverius) in the Imperial Valley, California

Gregarious Winter Roosting and Early Morning Perching Behavior of American Kestrels (<i>Falco sparverius</i>) in the Imperial Valley, California

Abundance and Distribution of Overwintering Red-tailed Hawks and American Kestrels in an Agricultural Landscape in Northeastern Arkansas

Abstract Although Red-tailed Hawks (Buteo jamaicensis) and American Kestrels (Falco sparverius) are common raptors in the U.S.A., their wintering population abundance and distribution has not been studied recently in Arkansas. We assessed the temporal and spatial variation in population abundance of Red-tailed Hawks and American Kestrels over the winter in northeastern Arkansas. We conducted weekly surveys from an automobile in Craighead and Poinsett counties, Arkansas, October 2012–March 2013. Abundance of Red-tailed Hawks (n = 854 total observations) and American Kestrels (n = 165 total observations) along the transect increased during winter months. The overall abundance indices were 7.05 Red-tailed Hawks per 10 km (highest ever recorded) and 1.36 American Kestrels per 10 km. We found no significant differences in the utilization of the various cover types (i.e., short rice stubble, soybean stubble, and fallow areas/roadsides) for either species. However, both species differed in their use of perch...

A redescription of the feather mite, Dubininia accipitrina (Trouessart, 1885) (Acari: Xolalgidae), parasitizing falcons (Falconiformes: Falconidae)

Dubininia accipitrina (Trouessart, 1885) is the type species of the feather mite genus Dubininia Vassilev, 1958 (Xolalgidae: Ingrassiinae), infesting various falcons of the genus Falco Linnaeus. This species is redescribed based on samples from the American Kestrel Falco sparverius Linnaeus (Falconiformes: Falconidae).