Peregrine Research Articles

Peregrine falcons shift mean and variance in provisioning in response to increasing brood demand.

The hierarchical model of provisioning posits that parents employ a strategic, sequential use of three provisioning tactics as offspring demand increases (e.g., due to increasing brood size and age). Namely, increasing delivery rate (reducing intervals between provisioning visits), expanding provisioned diet breadth, and adopting variance-sensitive provisioning. We evaluated this model in an Arctic breeding population of Peregrine falcons (Falco peregrinus tundrius) by analyzing changes in inter-visit-intervals (IVIs) and residual variance in IVIs across 7 study years. Data were collected using motion-sensitive nest camera images and analyzed using Bayesian mixed effect models. We found strong support for a decrease in IVIs (i.e., increase in delivery rates) between provisioning visits and an increase in residual variance in IVIs with increasing nestling age, consistent with the notion that peregrines shift to variance-prone provisioning strategies with increasing nestling demand. However, support for predictions made based on the hierarchical model of tactics for coping with increased brood demand was equivocal as we did not find evidence in support of expected covariances between random effects (i.e., between IVI to an average sized brood (intercept), change in IVI with brood demand (slope) or variance in IVI). Overall, our study provides important biological insights into how parents cope with increased brood demand.

Numerical and experimental investigation of airfoil derived from peregrine FALCON

In this work, the Peregrine falcon's airfoil is derived and is analysed numerically and experimentally in a non-flapping, non-morphing case. The airfoil is analysed numerically using a Steady State RANS k-ω SST model at different Reynolds numbers with ANSYS Fluent solver and is compared with NACA 23015 and NACA 64–210. The numerical method of approach is validated at a high Reynolds number of 1x106 experimentally. The results dictate that FALCON airfoil has a cl, max that is 54 % and 118 % higher than NACA 23015 and NACA 64–210 respectively. Stalling at 12oangle of attack, the airfoil generates an (LD) of 84, and produces positive lift coefficients till -5o angle of attack. The cl of FALCON is higher than the NACA 64–210 and 23015 at all angles of attack. The variation of (LD) with AoA is smooth and of a parabolic nature than an abrupt one.

Diet Specialization in an Insular Population of Coastal Peregrine Falcons

Individual diet specialization is known to occur in populations of generalist predators, where specific individuals develop specialist feeding strategies. Diet specialization has been reported in many raptor species and it may be an important driver of intraspecific population structure. Here, we quantify the diet of Peregrine Falcons Falco peregrinus from five breeding territories on an island determined from prey remains collected over four breeding seasons. Three prey species accounted for 69.8% of total prey frequency, with Manx Shearwater Puffinus puffinus being the primary prey accounting for 47.3% by frequency and 40.8% by biomass. European Herring Gull Larus argentatus was the second most important prey species by frequency (13.8%) and biomass (29.8%) followed by Feral Pigeon Columba livia (frequency: 8.7%, biomass: 7.0%). Prey frequency on specific prey groups varied substantially between breeding pairs and months. Two pairs specialized on Manx Shearwater, one pair specialized on Herring Gull and Manx Shearwater, with the remaining two pairs having a relatively generalist diet of Manx Shearwaters, Feral Pigeon and small passerines. Prey frequency on Manx Shearwaters increased throughout the breeding season with a peak in total diet frequency of 63.8% in July, with a concurrent decrease in Herring Gull prey frequency. Higher percentage of Manx Shearwater in the diet explained 87% of the variation in a narrower dietary breadth for the Peregrine pairs. Our results suggest individual diet specialization may be one of multiple factors important for understanding population density in insular raptor populations.

Numerical study on the hydrodynamic lubrication performance improvement of bio-inspired peregrine falcon wing-shaped microtexture

Bio-inspired surface microtexture has been adopted in mechanical systems for its advanced lubrication performance. In this study, we discerned the aerodynamic characteristics of different parts of the peregrine falcon’s wing, summarized the influence of its distinctive shape on the fluid flow, and, based on simplified geometries and the bionic concept, designed a novel wing-shaped microtexture to enhance lubrication performance in friction pairs. Its shape was simplified by the following parameters: area ratio Sp, dimensionless depth h*, and orientation angle α. Using a multiphase flow model, we investigated the effect of the above geometrical parameters on the lubrication performance of the wing-shaped microtexture by numerical simulation. The corresponding geometrical parameters of the wing-shaped microtexture to achieve optimum lubrication performance were: Sp = 30%/h*=1.75/α = 0°. The wing-shaped microtexture’s friction coefficient(COF) corresponded to a reduction of 18.8% and 20.7%, respectively, compared to the triangle and rectangular microtexture, which had the best lubrication performance for existing applications. The results showed that the wing-shaped microtexture enhanced the lubrication performance for three reasons: 1. The biomimetic leading edge created more negative pressure and cavitation zones; 2. The interference between positive and negative pressure zones was effectively mitigated; 3. The sharp design of the biomimetic trailing edge and tail wing concentrated the positive pressure zone while increasing its area. Two double-layer composite wing-shaped microtextures were further introduced to maximize friction reduction. The impact of inner-outer layer area ratio Sp* and inner-outer depth ratio h* on the lubrication performance was investigated. Their simulation results revealed that the optimal geometric parameters for the composite microtextures were Sp*=6.3%/hp*=3.0 and Sp*=12.7%/hp*=2.0, respectively. The configurations led to additional COF reductions of 7.6% and 10.56% compared to the single-layer wing-shaped microtexture. These insights offer valuable guidance for reducing friction and wear in mechanical systems.

Quantitative analysis of the morphing wing mechanism of raptors: IMMU-based motion capture system and its application on gestures of a Falco peregrinus

This paper presented a novel tinny motion capture system for measuring bird posture based on inertial and magnetic measurement units that are made up of micromachined gyroscopes, accelerometers, and magnetometers. Multiple quaternion-based extended Kalman filters were implemented to estimate the absolute orientations to achieve high accuracy. Under the guidance of ornithology experts, the extending/contracting motions and flapping cycles were recorded using the developed motion capture system, and the orientation of each bone was also analyzed. The captured flapping gesture of the Falco peregrinus is crucial to the motion database of raptors as well as the bionic design.

Rewilding the Detroit, Michigan, USA–Windsor, Ontario, Canada Metropolitan Area

Rewilding attempts to increase biodiversity and restore natural ecosystem processes by reducing human influence. Today, there is growing interest in rewilding urban areas. Rewilding of the Detroit, Michigan, USA and Windsor, Ontario, Canada metropolitan area, and its shared natural resource called the Detroit River, has been delineated through the reintroduction of peregrine falcons and osprey, and a return of other sentinel species like bald eagles, lake sturgeon, lake whitefish, walleye, beaver, and river otter. Rewilding has helped showcase the value and benefits of environmental protection and restoration, ecosystem services, habitat rehabilitation and enhancement, and conservation, including social and economic benefits. Improved ecosystem health and rewilding have become a catalyst for re-establishing a reconnection between urban denizens and natural resources through greenways and water trails. The provision of compelling outdoor experiences in nature, in turn, can help foster a personal attachment to the particular place people call home that can help inspire a stewardship ethic.

Reproductive performance of Peregrine falcons relative to the use of organochlorine pesticides, 1946-2021.

Populations of some fish- and meat-eating birds suffered dramatic declines globally following the introduction of organochlorine pesticides during the late 1940s and 1950s. It has been hypothesised that these population declines during the 1950s-1970s were largely driven by a combination of reproductive failure due to eggshell-thinning, egg breakage and embryonic death attributable to DDT and its metabolites, and to enhanced mortality attributable to the more toxic cyclodiene compounds such as aldrin and dieldrin. Using 75 years (1946-2021) of Peregrine falcon (Falco peregrinus) monitoring data (315 unique nest-sites monitored for 6110 nest-years), we studied the breeding performance of a resident Peregrine population in southern Scotland relative to the spatiotemporal pattern of organochlorine pesticide use. We show that (i) Peregrine breeding success and measures of breeding performance increased substantially following the reduction in, and subsequently a complete ban on, the use of organochlorine pesticides; (ii) improvements in Peregrine breeding performance were more dramatic in southeastern Scotland where agriculture was the predominant land use than in southwestern Scotland where there was less arable and more forested land; (iii) Peregrines nesting closer to the coast generally had higher fledging success (that is, a higher proportion of clutches that produced at least one fledgeling) than those nesting inland farther away from the coast; (iv) low temperatures and excessive rain in May negatively affected Peregrine fledging success; and (v) Peregrine abundance increased in parallel with improvements in reproductive performance following the reduction and then complete ban on the use of organochlorine pesticides in the UK. However, recovery was gradual and occurred over four decades, and rate of recovery varied among measures of reproductive performance (egg, nestling and fledgeling production). Our results suggest that the temporal pattern of organochlorine pesticide use strongly influenced Peregrine reproductive parameters but that the pattern of influence differed regionally. Overall results are consistent with the hypothesis that reproductive failure caused by organochlorine pesticides was an important driver of the decline in the south Scottish Peregrine population, and that improvements in all measures of breeding performance following a reduction and eventual ban on organochlorine use facilitated the observed increase in this population.

Trends in the global trade of live CITES-listed raptors: Trade volumes, spatiotemporal dynamics and conservation implications

The global legal wildlife trade is worth US$4–20 billion to the world's economy every year. Raptors frequently enter the wildlife trade for use as display animals, by falconers or hobbyists for sport and recreation. Using data from the Convention on International Trade in Endangered Species of Wild Fauna and Flora's (CITES) Trade Database, we examined trends in the global, legal commercial trade of CITES-listed raptors between 1975 and 2020. Overall 272 species were traded, totalling 188,149 traded individuals, which increased over time. Hybrid Falcons (N = 50,366) were most commonly traded, comprising more than a third of the global diurnal CITES-listed raptor trade, followed by Gyrfalcons (Falco rusticolus; N = 30,510), Saker Falcons (F. cherrug; N = 21,679), Peregrine Falcons (F. peregrinus; N = 13,390) and Northern White-faced Owls (Ptilopsis leucotis; N = 6725). More than half of wild-caught diurnal raptors were classified as globally threatened. The United Kingdom was the largest exporter of live raptors and the United Arab Emirates was the largest importer. Countries with higher GDPs (US$) imported more raptors than those with smaller GDPs. Larger-bodied diurnal species were traded more relative to smaller-bodied conspecifics. Following the introduction of the European Union's Wild Bird Trade Ban in 2005, the number of traded wild-caught raptors declined. Despite its limitations, the CITES Trade Database provides an important baseline of the global legal trade of live raptors. However, better understanding of illegal wildlife trade networks and smuggling routes, both on-the-ground and online, are essential for future conservation efforts.

Whole-genome survey reveals extensive variation in genetic diversity and inbreeding levels among peregrine falcon subspecies.

In efforts to prevent extinction, resource managers are often tasked with increasing genetic diversity in a population of concern to prevent inbreeding depression or improve adaptive potential in a changing environment. The assumption that all small populations require measures to increase their genetic diversity may be unwarranted, and limited resources for conservation may be better utilized elsewhere. We test this assumption in a case study focused on the peregrine falcon (Falco peregrinus), a cosmopolitan circumpolar species with 19 named subspecies. We used whole-genome resequencing to generate over two million single nucleotide polymorphisms (SNPs) from multiple individuals of all peregrine falcon subspecies. Our analyses revealed extensive variation among subspecies, with many island-restricted and nonmigratory populations possessing lower overall genomic diversity, elevated inbreeding coefficients (F ROH)-among the highest reported, and extensive runs of homozygosity (ROH) compared to mainland and migratory populations. Similarly, the majority of subspecies that are either nonmigratory or restricted to islands show a much longer history of low effective population size (N e). While mutational load analyses indicated an increased proportion of homozygous-derived deleterious variants (i.e., drift load) among nonmigrant and island populations compared to those that are migrant or reside on the mainland, no significant differences in the proportion of heterozygous deleterious variants (i.e., inbreeding load) was observed. Our results provide evidence that high levels of inbreeding may not be an existential threat for some populations or taxa. Additional factors such as the timing and severity of population declines are important to consider in management decisions about extinction potential.

Avian wings can lengthen rather than shorten in response to increased migratory predation danger.

Increasing predation danger can select for safety-enhancing modifications to prey morphology. Here, we document the multi-decade wing lengthening of a Pacific flyway migrant, the western sandpiper (Calidris mauri), and contrast this with contemporaneous wing shortening of the closely related semipalmated sandpiper (C. pusilla) on the Atlantic flyway. We measured >12,000 southbound western sandpipers captured from 1978 to 2020 at a major stopover site in British Columbia. Wing length increased at 0.074 mm year-1 (SE = 0.017; p < .0003) for adults, and 0.087 mm year-1 (SE = 0.029; p < .007) for juveniles. These rates are of similarly large magnitude (4%-5% overall), but opposite in direction, to the rate we previously reported for semipalmated sandpiper adults (-0.103 mm year-1). In both species, the change is specific to wings rather than being part of a general body size change. We interpret both trends as responses to the ongoing strong increase of peregrine falcon (Falco peregrinus) populations since the mid-1970s, an important predator encountered by these species in contrasting ways during migration. Western sandpipers and peregrine migrations have temporal and spatial overlap. Longer wings enhance migratory speed and efficiency, enabling western sandpipers to decrease overlap by advancing to safer zones ahead of falcon passage. In contrast, semipalmated sandpipers primarily encounter peregrines as residents at migratory staging sites. Shorter wings improve acceleration and agility, helping migrants to escape attacks. Juvenile western sandpiper wing length also shows a component additive to the lengthening trend, shifting between years at 0.055 mm day-1 with the highly variable snowmelt date, with wings shorter following early springs. On the Pacific flyway, the timing of peregrine southward passage advances with snowmelt, increasing the relative exposure of juveniles to post-migratory resident peregrines. We interpret this annual wing length adjustment as an induced defense, made possible because snowmelt timing is a reliable cue to danger in the upcoming migration.

Experimental Analysis of Bio-Inspired Vortex Generators on a Blade with S822 Airfoil

Vortex generators are used in aircraft wings and wind turbine blades. These devices allow them to maintain a stable turbulent behavior in the wind wake. Vortex generators, or VGs, improve the transition from laminar to turbulent boundary layer regime, avoiding abrupt shedding. HAWT wind turbines have high rotational velocity. Currently, HAWT turbines are being redesigned with fixed vortex generators, achieving higher energy production. This paper presents a wind tunnel analysis of a fixed-wire blade with S822 airfoil and active VGs bio-inspired by the flight-stabilizing feathers of the peregrine falcon. Vibrations measured on the blade show a reduction in intensity at wind velocities close to 15 m/s. The measured wake velocities show fluctuations at higher tunnel wind velocities. An FFT spectral analysis of the wind wake velocities showed differences between the spectral components. When activating the VGs in oscillation at a constant frequency, a reduction of the vibrations on the blade was observed for wind velocities around 20 m/s.

Avian influenza overview March – April 2023

Between 2 March and 28 April 2023, highly pathogenic avian influenza (HPAI) A(H5Nx) virus, clade 2.3.4.4b, outbreaks were reported in domestic (106) and wild (610) birds across 24 countries in Europe. Poultry outbreaks occurred less frequently compared to the previous reporting period and compared to spring 2022. Most of these outbreaks were classified as primary outbreaks without secondary spread and some of them associated with atypical disease presentation, in particular low mortality. In wild birds, black-headed gulls continued to be heavily affected, while also other threatened wild bird species, such as the peregrine falcon, showed increased mortality. The ongoing epidemic in black-headed gulls, many of which breed inland, may increase the risk for poultry, especially in July-August, when first-year birds disperse from the breeding colonies. HPAI A(H5N1) virus also continued to expand in the Americas, including in mammalian species, and is expected to reach the Antarctic in the near future. HPAI virus infections were detected in six mammal species, particularly in marine mammals and mustelids, for the first time, while the viruses currently circulating in Europe retain a preferential binding for avian-like receptors. Since 13 March 2022 and as of 10 May 2023, two A(H5N1) clade 2.3.4.4b virus detections in humans were reported from China (1), and Chile (1), as well as three A(H9N2) and one A(H3N8) human infections in China. The risk of infection with currently circulating avian H5 influenza viruses of clade 2.3.4.4b in Europe remains low for the general population in the EU/EEA, and low to moderate for occupationally or otherwise exposed people.

Avian species survey with citizen-science data in Janghang Wetland, Goyang, Republic of Korea.

Monitoring of avian populations in Janghang Wetland, Goyang, Republic of Korea (ROK) is based on citizen science (also called community-based monitoring). This monitoring data can be used to track avian density, population status and waterbird census at local, national and regional levels. The Ministry of Environment (MoE) ROK has surveyed since 1999, including Odusan Unification Tower to Ilsan Bride, which connects the cities of Gimpo and Goyang along the Han River estuary. However, it has not covered Janghang Wetland, which is located in the Han River estuary at the transboundary between the two Koreas. The Janghang Wetland is a protected wetland in the Demilitarized Zone (DMZ) between the two Koreas. In 2019, Janghang Wetland was designated as a Flyway Network Site by Goyang City and the East Asian-Australasian Flyway Partnership. This Network site is a voluntary collaboration and includes many internationally significant wetlands for waterbirds that still lack formal national protection. In addition, it was designated as a Ramsar site in 2021. The wetland currently supports wintering population of White-naped Crane (Grusvipio), species listed as vulnerable and Tundra Bean Goose (Ansercygnoides), spring-autumn migration population of Swan Goose (Ansercygnoid), species listed as vulnerable and a breeding population of Black-faced Spoonbill (Plataleaminor), species listed as endangered in summer. We provide data that the Janghang Wetland is a significant area for migration and breeding for waterbirds; and that Han River estuary is also internationally important for waterbirds during the migratory bird season. We observed 14 orders, 42 families and 132 species. The surveys also observed the critically-endangered Black-faced Spoonbill (Plataleaminor), Swan Goose (Ansercygnoides), White-naped Crane (Grusvipio), Whooper Swan (Cygnuscygnus) and Peregrine Falcon (Falcoperegrinus). We also observed the Black-faced Spoonbill, Great Egret, Little Egret, Great Cormorant, Eastern Spot-billed Duck, Pheasant and Brown-eared Bulbul at the sensor camera point and White-naped Crane, Hooded Crane, Bean Goose, White-fronted Goose, Snow Goose, Swan Goose, Great Cormorant and Eastern Spot-billed Duck at the closed-circuit television camera point from the camera-trap surveys. Based on the species recorded, the survey area is of clear importance for biodiversity conservation.

Community structure of raptors in the páramo landscape of the Ecuadorian Andes

Introduction: Habitat alterations result in biodiversity loss, particularly in regions with high levels of diversity and endemism. Raptors are an essential part of the functionality and stability of ecosystems and indicators of habitat quality. In the paramo grassland ecosystems in the high Andes of Northern South America, raptors contain a high concentration of threatened species. Objective: To describe the raptor community structure and determine the species associations. Methods: We made monthly raptor counts in eight transects from October 2021 to September 2022 and used a principal component analysis to determine species associations. Results: We identified 149 individuals (seven species, three families) in two communities: abundant (Carunculated Caracara, Variable Hawk, Andean Condor and Turkey Vulture; PCI = 47 %), and scarce (Cinereous Harrier, Peregrine Falcon and Aplomado Falco; PCII = 27 %). Conclusion: We provide a valid description and understanding of raptor community structure, identifying two communities and the dynamics between them. The first is characterized by an increased abundance of generalist and regionally common species, when the abundance of these species decreases, the second community is defined, characterized by an increase in the abundance of specialist and rare species at the local scale.

TESTING STELLA DYNAMIC MODELING PACKAGE FOR THREATENED PEREGRINE FALCON POPULATION ASSESSMENT

The Peregrine Falcon (Falco peregrinus) is the world's most widely distributed avian predator, which also inhabits various natural ecosystems of Armenia. In the past, the Peregrines faced a dramatic decline in the mid-20th century being affected by pesticides used in agriculture and forestry. Today, in Armenia, the species is rather vulnerable from the pollution of mining industry, municipal dumps, pollution by pesticides, and potentially, from illegal trade for falconry, therefore its population needs proper assessment. Population modeling is one of the novel and precise assessment methods, which can serve for more effective species conservation. The existing estimation of Peregrine’s population in Armenia was not based on a comprehensive model, which considers such aspects as food sources, potential risks, and actual threats. Thus, in our study, we have developed and tested a model, which includes the following parameters that potentially can impact the population’s growth and reduction: nest competitors, food competitors, potential prey species, juvenile predators, poachers, and pesticides used to manage forest pests. Modeling of Peregrine’s population in Armenia was conducted using Euler’s method in frames of the STELLA package. The model demonstrated a decrease of Peregrine Falcons’ population in the south of Syunik with its potential vanishing in the next 25 years. The field observations confirmed the predicted decline in some extent.

Illegal Trade in Exotic Animals and Its Impacts in Slovenia-A Case Study.

Currently, the illegal wildlife trade is one of the most profitable illegal enterprises in the world. The aim of our study was to determine the situation with respect to wildlife trade in Slovenia, which is mainly a transit country, before changes to the Schengen borders came into effect. The volume of trade is significant but not extensive. The most common endangered species involved in illegal trade in Slovenia are the brown bear, the peregrine falcon, the date mussel, the lady's slipper orchid, the common snowdrop, the cyclamen, the sea turtle, the otter, and various reptile species. The smuggling of shells (date shells), ivory (ivory products), certain plants, and various hunting trophies (bears, big cats) has decreased in recent years. Nevertheless, counteracting crimes continues to be important for the conservation of some species in Slovenia, notably the lynx, and for the reduction of poaching. Improvements are needed in the detection and prevention of wildlife crime, especially in light of changes made to the Schengen borders and the consequent inclusion of new trading partners for Slovenia. The lack of people properly trained to identify, detect, and investigate wildlife crime is especially acute.

PEREGRINE FALCON FALCO PEREGRINUS IN BRAZIL: NATURAL HISTORY THROUGH THE LENS OF CITIZEN SCIENCE

Brazil is a relevant wintering area for Falco peregrinus, particularly the subspecies F. p. tundrius and F. p anatum. Using data from WikiAves, we analyzed and discussed aspects of the species natural history, such as their migratory behavior, geographical distribution, diet, and ecological interactions. Peregrine falcons can be seen in the country from October until April. Our data suggests that adults can arrive up to a month earlier than juveniles. Individuals have been recorded in all 26 states and there is no significant difference in the geographical distribution due their subspecies or age, but there is an apparent lack of records on Central region of the country. Our results shows that in Brazil peregrines prey mainly on Columbiformes and Charadriiformes. Some individuals share the same perch and engage on agonistic interactions with other bird species, usually mopping or kleptoparasitism.

Computer-assisted semen analysis in large falcons (Falco spp.) and comparison to results of conventional semen analysis

Numerous raptor species including some falcon species are facing continuous population decline in the wild and some are threatened by extinction. To support these species, captive breeding and reintroduction programs are attempted. Besides conservation, some large falcon species are commonly used in falconry and therefore bred commercially. Assisted reproduction is established in falcon breeding since the 1970s and semen analysis is an integral part to enable assessment of breeding males, inclusion or exclusion of semen donors and quality control of semen prior to artificial insemination. Conventional methods for semen analysis are widely used, but are time consuming and depend on the investigator's experience and ability. Computer-assisted semen analysis (CASA) would offer an objective, fast and reproducible alternative, but as they have not been established in large falcon species, this was the aim of this study. To this end, we examined in 3 breeding seasons 109 semen samples of gyr-saker hybrid falcons (n=2) and peregrine falcons (n=4) in 940 fields of view using the Minitube CASA SpermVision and compared these results to results of conventional methods of semen analysis. We used a preprogrammed setting and adapted two settings of CASA according to specific semen characteristics of falcons. Sperm velocity, motility and viability parameters were recorded successfully using CASA. Correlation of conventional and computer-assisted motility analysis improved during the process of adaptation of CASA settings, but both methods differed significantly due to misinterpretation of round bodies and semen impurities by CASA. Viability values of conventional and computer assisted viability analysis using SYBR-PI correlated significantly while sperm concentration did not at all. CASA failed to replace conventional semen analysis regarding sperm motility and sperm concentration using 3 different settings, as a reliable differentiation between spermatozoa, spermatids and round bodies was not achieved. Using CASA, sperm velocity parameters were measured in spermatozoa of captive-bred large falcons for the first time and may be used as orientation values.

Predation danger during active migration: insights from a tagged Bar-tailed Godwit depredated by a breeding Peregrine Falcon

Predation danger during active migration: insights from a tagged Bar-tailed Godwit depredated by a breeding Peregrine Falcon

Redescription of Serratospiculum tendo (Nietzsch, 1819) (Nematoda: Diplotriaenidae) from the Peregrine Falcon (Falco peregrinus Tunstall, 1771) from Dubai, United Arab Emirates

The redescription of Serratospiculum tendo is based on specimens taken from 4 female and 6 male peregrine falcons (Falco peregrinus Tunstall). This redescription was necessary since previous morphological characterizations were only based on single nematodes, and important details such as the position of the excretory pore in males and females, description of the female reproductive system, and the size of the posterior caudal disc of males were not given. Serratospiculum tendo differs from its 2 congeners (Serratospiculum seurati and Serratospiculum guttatum) by a longer body length of males and females (113–166 and 293–340 mm, respectively) and longer right and left spicules (452–531 and 1,104–1,341 µm, respectively). In comparison, the body length of male and female specimens of S. seurati is 30–79 mm and 165–220 mm, respectively, and the spicules of the males measured 312–415 and 674–887 µm, respectively. The absence of cuticular bosses in S. tendo and S. seurati is a criterion to differentiate these species from S. guttatum.