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Birds aim to optimize resources for feeding young and self-maintenance by timing reproduction to coincide with peak food availability. When reproduction is mistimed, birds could incur costs that affect their survival. We studied whether nesting phenology correlated with the apparent survival of American kestrels (Falco sparverius) from two distinct populations and examined trends in clutch-initiation dates. We estimated apparent survival using multi-state mark-recapture models with nesting timing, nesting success, sex, age, and weather covariates. Nesting timing predicted the apparent survival of successful adults; however, the effect differed between populations. Early nesting kestrels had higher apparent survival than later nesters in the western population, where kestrels have a relatively long nesting season. At the eastern site, where kestrels have a relatively short nesting season, the pattern was reversed—later nesters had higher apparent survival than earlier nesters. Nesting timing did not affect the apparent survival of adults with failed nests suggesting that the energetic cost of producing fledglings contributed to the timing effect. Finally, clutch-initiation dates advanced in the western population and remained static in the eastern population. Given that both populations have seasonal declines in productivity, population-specific survival patterns provide insight into seasonal trade-offs. Specifically, nesting timing effects on survival paralleled productivity declines in the western population and inverse patterns of survival and reproduction in the eastern population suggest a condition-dependent trade-off. Concomitant seasonal declines in reproduction and survival may facilitate population-level responses to earlier springs, whereas seasonal trade-offs may constrain phenology shifts and increase vulnerability to mismatch.

1. The rapid increase of human activity in wild and developed areas presents novel challenges for wildlife. Some species may use human-dominated landscapes because of favourable resources (e.g. high prey availability along roadsides); however, use of these areas may increase exposure to anthropogenic stressors, such as human disturbance or noise, which can negatively affect reproduction or survival. In this case, human-dominated landscapes may act as an ecological trap. 2. We evaluated whether American kestrel Falco sparverius reproductive failure was associated with human disturbance (traffic conditions and land development) or other common predictors of reproductive outcome, such as habitat and clutch initiation date. Also, we examined relationships among human disturbance, corticosterone (CORT) concentrations and nest abandonment to explore potential mechanisms for stress-induced reproductive failure. 3. Twenty-six (36%) of 73 kestrel nesting attempts failed and 88% of failures occurred during incubation. Kestrels nesting in higher disturbance areas were 9·9 times more likely to fail than kestrels nesting in lower disturbance areas. Habitat and clutch initiation date did not explain reproductive outcome. 4. Females in higher disturbance areas had higher CORT and were more likely to abandon nests than females in lower disturbance areas. There was no relationship between male CORT and disturbance or abandonment. Females spent more time incubating than males and may have had more exposure to anthropogenic stressors. Specifically, traffic noise may affect a cavity-nesting bird's perception of the outside environment by masking auditory cues. In response, incubating birds may perceive a greater predation risk, increase vigilance behaviour, decrease parental care, or both. 5. Synthesis and applications. Proximity to large, busy roads and developed areas negatively affected kestrel reproduction by causing increased stress hormones that promoted nest abandonment. These results demonstrate that species presence in a human-dominated landscape does not necessarily indicate a tolerance for anthropogenic stressors. Managers should carefully consider or discourage projects that juxtapose favourable habitat conditions with areas of high human activity to decrease risk of ecological traps. Noise mitigation, while locally effective, may not protect widespread populations from the pervasive threat of traffic noise. Innovative engineering that decreases anthropogenic noise at its source is necessary.

Wind energy development is advancing rapidly, but the potential ramifications of this growth on wildlife, particularly birds and bats, are not fully understood. Wind energy development may affect raptor (birds of prey) populations indirectly by displacing them from their previously occupied habitat; however, there are limited empirical data demonstrating this effect. We performed long-term raptor surveys at a wind farm previously implicated in the displacement of resident raptors and found that the duration of displacement varied among raptor species. Abundances of turkey vultures (Cathartes aura), red-tailed hawks (Buteo jamaicensis), and accipiters (sharp-shinned hawks [Accipiter striatus] and Cooper’s hawks [Accipiter cooperii] combined) all rebounded in years 7 and 8 of wind farm operation, while the apparent displacement of northern harriers (Circus hudsonius) and American kestrels (Falco sparverius) persisted across all post-construction monitoring periods. Our long-term assessment indicates not only that wind farm construction and operation may displace raptors but also that these impacts can diminish over time for certain species. This finding underscores the importance of assessing potential impacts over the operational life of a given wind farm and the need for long-term monitoring to validate predicted impacts, particularly for raptor communities.

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.

1. Suppression of pest species via a native predator is a regulating ecosystem service that has the potential to limit crop damage and produce economic benefits. American kestrels Falco sparverius are widespread, highly mobile, generalist predators that hunt in human-dominated habitats and have the potential to provide previously undocumented ecosystem services in agricultural landscapes. 2. We hypothesized that kestrel activity associated with nest boxes and artificial perches acts to increase perceived predation risk that, in combination with direct predation, can reduce fruit-eating bird abundances in orchards. We used counts and observations of fruit-eating birds from fixed-width transect surveys to investigate variation in bird abundances and to estimate sweet cherry loss in cherry orchards with and without active kestrel boxes. We also conducted a benefit-cost analysis of nest box installation and used regional economic modelling to estimate macroeconomic impacts of increased sweet cherry production in Michigan, an important US fruit production region. 3. Fruit-eating bird counts were significantly lower at orchards with active kestrel boxes. Although kestrels used the perches in young orchard blocks and may benefit from them, the presence of perches did not have a significant effect on bird counts. 4. Benefit-cost ratios for kestrel nest boxes indicated that for every dollar spent on nest boxes, $84 to $357 of sweet cherries would be saved from fruit-eating birds. Regional economic modelling predicted that increased sweet cherry production from reduced bird damage would result in 46-50 jobs created and $2.2 million to $2.4 million in increased income for the state of Michigan over a 5-year period. 5. Synthesis and applications. Kestrel nest boxes in sweet cherry orchards provide a highly cost-effective ecosystem service with potential reverberating benefits for a regional economy. Box occupancy rates will undoubtedly vary across landscapes and regions. However, costs to install and maintain boxes are small and, even if box occupancy rates are low, boxes can direct kestrel activity to particular places in agricultural landscapes where they can deter pest birds. Thus, the potential benefits for fruit crops greatly outweigh the costs of this pest management strategy.

Parasite communities vary among host species and across space. However, little is known about differences in parasite communities between geographically and genetically distinct populations of the same host species. American kestrels ( Falco sparverius ) are small falcons with regionally distinct genetic populations across North America. We sampled kestrels from Delaware and Utah for avian haemosporidian parasites (genera: Haemoproteus , Plasmodium , and Leucocytozoon ) and used molecular barcoding of the parasite cytochrome b gene (cyt b ) to quantify parasite genetic lineage diversity. We identified four lineages of Haemoproteus parasites and one Leucocytozoon lineage infecting kestrels. A comparison with previous studies suggests that most of these lineages are largely restricted to kestrels. We found similar infection prevalence and lineage composition between the sites. All kestrels sampled in Utah were adults (i.e., sampled after hatch year), but in Delaware, we found adult birds had a higher infection prevalence than juveniles (i.e., hatch-year birds). Despite harboring largely the same parasite lineages, kestrels are unlikely to disperse between Utah and Delaware. The similarity in parasite lineages in the two kestrel populations could be due to a number of factors including broadly distributed vector species (of which little is known), movement of alternative and undetected host species, or transmission during migration or on overwintering grounds. Alternatively, the cyt b gene might not capture recent genetic differentiation among the parasites. Future studies should explore these various possibilities to understand the mechanisms underpinning parasite distributions across genetically structured host populations.

The American kestrel ( Falco sparverius , hereafter referred to as kestrel) has declined across much of its North American range since at least the mid‐1960s. Kestrel population dynamics have been explored through a multitude of local studies and two broad reviews of available data. Across large geographic extents, however, the demographic cause(s) of kestrel population declines remain(s) largely unknown. As part of a collaborative effort to elucidate the drivers of kestrel population declines, we developed a continental‐scale integrated population model using band‐recovery data, productivity data, and Breeding Bird Survey indices from 1986 to 2019 to estimate indices of annual population sizes, survival, and productivity rates across the continental United States. We detected a decline in population size of ~1%–2% per year. Overall estimates of population growth from 1986 to 2019 suggest a 29% decline in population size (95% CI = −34% to −23%). There was little evidence of a trend in brood size. However, survival of juvenile birds (mean = −0.015, SD = 0.008 and mean = −0.024, SD = 0.010 for females and males, respectively) and adult males (mean = −0.016, SD = 0.010) in the summer declined, suggesting that these vital rates could be contributing to declines in populations over time. Winter adult survival rates (mean = −0.004, SD = 0.009 and mean = −0.009, SD = 0.010 for females and males, respectively) also declined but to a lesser extent than summer survival. For juvenile birds, winter survival increased (mean = 0.006, SD = 0.008 and mean = 0.002, SD = 0.009 for females and males, respectively); however, this was not enough to offset declines in summer survival and annual survival rates declined over the time series. Annual adult survival was also low relative to previous research on kestrel survival rates. Given the importance of survival to population trends, our findings provide support for several previously proposed broad classes of factors potentially contributing to observed population declines: declines in arthropod prey, second‐generation rodenticides, neonicotinoid insecticides, and predation.

Anticoagulant rodenticides (ARs) are commonly used across the US to control rodent populations but may cause negative effects when secondarily consumed by raptors. Falco sparverius (American Kestrel) is a species of growing conservation concern due to widespread declines. We investigated AR exposure in American Kestrels by testing liver samples from 23 carcasses salvaged in Kentucky during 2014–2018. We confirmed exposure to 1 or more AR compounds in 57% of the birds examined. Rodenticides detected included brodifacoum, bromadiolone, and diphacinone. Brodifacoum was the most commonly detected AR, found in 92% of AR-positive birds. AR exposure was disparate among nestlings from 2 nests. None of the American Kestrels were diagnosed with AR toxicosis, but we found a significant association between poor nutritional condition and AR exposure. Our results indicate that secondary exposure to ARs in American Kestrels warrants more study as a potential contributor to population declines.

A central challenge in applied ecology is understanding the effect of anthropogenic fatalities on wildlife populations and predicting which populations may be particularly vulnerable and in greatest need of management attention. We used three approaches to investigate the potential effects of fatalities from collisions with wind turbines on 14 raptor species for both current (106 GW) and anticipated future (241 GW) levels of installed wind energy capacity in the United States. Our goals were to identify species at relatively high vs low risk of experiencing population declines from turbine collisions and to also compare results generated from these approaches. Two of the approaches used a calculated turbine‐caused mortality rate to decrement population growth, where population trends were derived either from the North American Breeding Bird Survey or from a matrix model parameterized from literature‐derived demographic values. The third approach was potential biological removal, which estimates the number of fatalities that allow a population to reach and maintain its optimal sustainable population set by management objectives. Different results among the methods reveal substantial gaps in knowledge and uncertainty in both demographic parameters and species‐specific estimates of fatalities from wind turbines. Our results suggest that, of the 14 species studied, those with relatively higher potential of population‐level impacts from wind turbine collisions included barn owl, ferruginous hawk, golden eagle, American kestrel, and red‐tailed hawk. Burrowing owl, Cooper’s hawk, great horned owl, northern harrier, turkey vulture, and osprey had a relatively lower potential for population impacts, and results were not easily interpretable for merlin, prairie falcon, and Swainson’s hawk. Projections of current levels of fatalities to future wind energy scenarios at 241 GW of installed capacity suggest some species could experience population declines because of turbine collisions. Populations of those species may benefit from research to identify tools to prevent or reduce raptor collisions with wind turbines.

We assessed total mercury (THg) concentrations in breast feathers of diurnal North American raptors collected at migration monitoring stations. For 9 species in the Pacific Flyway, we found species and age influenced feather THg concentrations whereas sex did not. Feather THg concentrations µg/g dry weight (dw) averaged (least squares mean ± standard error) higher for raptors that generally consume > 75% avian prey (sharp-shinned hawk Accipiter striatus: n = 113; 4.35 ± 0.45 µg/g dw, peregrine falcon Falco peregrinus: n = 12; 3.93 ± 1.11 µg/g dw, Cooper’s hawk Accipiter cooperii: n = 20; 2.35 ± 0.50 µg/g dw, and merlin Falco columbarius: n = 59; 1.75 ± 0.28 µg/g dw) than for raptors that generally consume < 75% avian prey (northern harrier Circus hudsonius: n = 112; 0.75 ± 0.10 µg/g dw, red-tailed hawk Buteo jamaicensis: n = 109; 0.56 ± 0.06 µg/g dw, American kestrel Falco sparverius: n = 16; 0.57 ± 0.14 µg/g dw, prairie falcon Falco mexicanus: n = 10; 0.41 ± 0.13 µg/g dw) except for red-shouldered hawks Buteo lineatus: n = 10; 1.94 ± 0.61 µg/g dw. Feather THg concentrations spanning 13-years (2002–2014) in the Pacific Flyway differed among 3 species, where THg increased for juvenile northern harrier, decreased for adult red-tailed hawk, and showed no trend for adult sharp-shinned hawk. Mean feather THg concentrations in juvenile merlin were greater in the Mississippi Flyway (n = 56; 2.14 ± 0.18 µg/g dw) than those in the Pacific Flyway (n = 49; 1.15 ± 0.11 µg/g dw) and Intermountain Flyway (n = 23; 1.14 ± 0.16 µg/g dw), and Atlantic Flyway (n = 38; 1.75 ± 0.19 µg/g dw) averaged greater than the Pacific Flyway. Our results indicate that raptor migration monitoring stations provide a cost-effective sampling opportunity for biomonitoring environmental contaminants within and between distinct migration corridors and across time.