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Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We conducted an annual late-summer raptor survey along a 53-km route around Henrys Lake Flats, Idaho, from 1994 to 2022, and pooled the resulting data with similar published information collected from 1974 to 1993. A mean of 36 Red-tailed Hawks (Buteo jamaicensis), 13 Ferruginous Hawks (Buteo regalis), and 16 Swainson's Hawks (Buteo swainsoni) were observed each year along this route. The counts of Ferruginous Hawks declined significantly (P < 0.001) over the combined study period and were almost 10 times lower from 2013–2022 compared to 1974–1983. The counts of Red-tailed Hawks also declined significantly (P = 0.04), whereas no significant variation was evident for Swainson's Hawks over the combined 49-yr study period. Summer precipitation levels and hawk numbers were not correlated. The observed numbers of Ferruginous Hawks and Red-tailed Hawks were correlated throughout the study period, suggesting similar responses to local environmental and/or land-use factors. Obvious changes in the study area during the corresponding 49 yr include conversion of some pastures to center-pivot-irrigated agriculture and a substantial expansion of all-terrain vehicle trails and recreational activity. Because 88% of Ferruginous Hawks breeding in the Columbia Basin funnel through the upper Snake River Plain and adjacent areas on their way to post-breeding ranges in the Great Plains, expanded surveys in these areas in late August/early September could effectively monitor this intermountain population. Realizamos un censo anual de rapaces en el final del verano a lo largo de una ruta de 53 km alrededor de las planicies del Lago Henrys, Idaho, desde 1994 hasta 2022, y combinamos los datos obtenidos con información similar publicada colectada entre 1974 y 1993. Se observó un promedio de 36 individuos de Buteo jamaicensis, 13 de B. regalis y 16 de B. swainsoni cada año a lo largo de esta ruta. Los conteos de B. regalis disminuyeron significativamente (P < 0.001) durante el período de estudio combinado y fueron casi 10 veces más bajos entre 2013–2022 en comparación con 1974–1983. Los conteos de B. jamaicensis también disminuyeron significativamente (P = 0.04), mientras que no se observó variación significativa en el caso de B. swainsoni durante el período de estudio combinado de 49 años. Los niveles de precipitación en verano y el número de individuos de Buteo no estuvieron correlacionados. Los números observados de B. regalis y B. jamaicensis estuvieron correlacionados durante todo el período de estudio, lo que sugiere respuestas similares a factores locales ambientales y/o de uso del suelo. Los cambios evidentes en el área de estudio durante los 49 años analizados incluyen la conversión de algunos pastizales a agricultura con sistemas de riego de pivote central y una expansión sustancial de caminos para vehículos todo terreno y actividad recreativa. Dado que el 88% de los individuos de B. regalis que se reproducen en la Cuenca de Columbia pasan por la parte alta de la planicie del Río Snake y áreas adyacentes en su camino a las áreas post reproductivas en las Grandes Llanuras, la ampliación de los censos en estas áreas a finales de agosto/principios de septiembre podrían permitir un seguimiento efectivo de esta población inter-montana. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Determining the sex of monomorphic species, such as Red-tailed Hawks (Buteo jamaicensis), can be very difficult in the field as the plumage of males and females is similar and body masses overlap between sexes. Our purpose was to develop age-class specific methods that could be used in field settings to accurately determine the sex of Red-tailed Hawks within an Upper Midwestern USA landscape. Red-tailed Hawk carcasses (n = 648) were grouped by age class, weighed, measured, and necropsied to determine the sex of each individual. We compared morphological measurements between males and females and used discriminant function analysis to identify morphological characteristics that were useful in sexing Red-tailed Hawks in-hand. We developed separate equations for hatch-year, second-year, after-second-year, and after-hatch-year Red-tailed Hawks that were 80–88% accurate in correctly classifying eastern Red-tailed Hawks (B. j. borealis) to sex. The region-specific methods we developed should be useful to raptor researchers and managers. Determinar el sexo de especies monomórficas, como Buteo jamaicensis, puede ser muy difícil en el campo, ya que el plumaje de los machos y las hembras es similar y las masas corporales se superponen entre los sexos. Nuestro propósito fue desarrollar métodos específicos por clase de edad que pudieran usarse en trabajos de campo para determinar con precisión el sexo de B. jamaicensis dentro de un paisaje del Medio Oeste Superior de EEUU. Los cadáveres de B. jamaicensis (n = 648) fueron agrupados por clase de edad, se pesaron, midieron y se les realizaron necropsias para determinar el sexo de cada individuo. Comparamos las medidas morfológicas entre machos y hembras y usamos análisis de función discriminante para identificar las características morfológicas que fueron útiles para asignar el sexo de los individuos en mano de B. jamaicensis. Desarrollamos ecuaciones separadas para individuos de B. jamaicensis dentro del año de eclosión, del segundo año, después del segundo año y después del año de eclosión que tuvieron una precisión del 80–88% para clasificar correctamente el sexo de los individuos de B. j. borealis del este. Los métodos específicos que desarrollamos para la región deberían ser útiles para los investigadores y gestores de rapaces. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

In many raptor species, hatching asynchrony results in a size hierarchy among nestlings, which may facilitate brood reduction by means of sibling aggression-induced mortality, especially in times of low food resources. However, few researchers have investigated the relationships among hatching asynchrony, sibling aggression, and nestling feeding rates in raptors. We studied the influence of hatch rank, brood size, and brood age on aggression and feeding rates among Red-shouldered Hawk (Buteo lineatus) nestlings in suburban southwestern Ohio. Despite relatively modest hatching asynchrony, nestling hatch rank (along with brood size and brood age) was an important predictor of the amount of aggression exhibited by individual nestlings. The oldest nestlings exhibited more aggressive behavior than younger nestlings, although they did not consume significantly more food. Aggression rates were higher in broods of three than broods of two nestlings, and aggression decreased from week 2 to week 3, post-hatching. However, hatch rank was not an important determinant of nestling food consumption, and food consumption rates were unrelated to sibling aggression rates. Identifiable prey delivered to nestling Red-shouldered Hawks was diverse and consisted of 28.3% birds, 25.7% mammals, 23.4% amphibians, 16.4% reptiles, and 6.2% invertebrates (by biomass). The relatively high percentage of birds in the diet may reflect food availability in the suburban habitat surrounding the nests. Sibling aggression did not result in direct siblicide in our study, but four nestlings apparently starved. Overall, the oldest Red-shouldered Hawk nestlings in our study established their dominance early but this was not associated with a detectable advantage in terms of food consumption. En muchas especies de aves rapaces, la asincronía en la eclosión da como resultado una jerarquía de tamaño entre los polluelos, lo que puede facilitar la reducción de la nidada por medio de la mortalidad inducida por la agresión entre hermanos, especialmente en épocas de bajos recursos alimenticios. Sin embargo, pocos investigadores han estudiado las relaciones entre la asincronía en la eclosión, la agresión entre hermanos y las tasas de alimentación de los polluelos en las aves rapaces. Estudiamos la influencia del ranking de eclosión, el tamaño de la nidada y la edad de la nidada en la agresión y las tasas de alimentación entre polluelos de Buteo lineatus en los suburbios del suroeste de Ohio. A pesar de una asincronía en la eclosión relativamente moderada, el ranking de eclosión de los polluelos (junto con el tamaño y la edad de la nidada) fue un predictor importante de la cantidad de agresión exhibida por los polluelos individuales. Los polluelos mayores exhibieron un comportamiento más agresivo que los polluelos más jóvenes, aunque no recibieron una cantidad significativamente mayor de alimento. Las tasas de agresión fueron más altas en las nidadas de tres que en las nidadas de dos polluelos, y la agresión disminuyó de la semana dos a la semana tres después de la eclosión. Sin embargo, el ranking de eclosión no fue un determinante importante del consumo de alimentos de los polluelos, y las tasas de consumo de alimentos no estuvieron relacionadas con las tasas de agresión entre hermanos. Las presas identificables entregadas a los polluelos de B. lineatus fueron diversas y consistieron en 28.3% de aves, 25.7% de mamíferos, 23.4% de anfibios, 16.4% de reptiles y 6.2% de invertebrados (por biomasa). El porcentaje relativamente alto de aves en la dieta puede reflejar la disponibilidad de alimentos en el hábitat suburbano que rodea los nidos. La agresión entre hermanos no resultó en un fratricidio directo en nuestro estudio, pero aparentemente cuatro polluelos murieron de hambre. En general, los polluelos más viejos de B. lineatus en nuestro estudio establecieron su dominancia de forma temprana, pero esto no se asoció con una ventaja detectable en términos de consumo de alimentos. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

Acoustic spatial capture-recapture (SCR) methods appear ideally suited for estimating population trends of cryptic species that are difficult to monitor. Despite evidence suggesting acoustic SCR offers greater precision over estimates obtained through distance sampling or mark-recapture approaches, it has seldom been applied to avian taxa. Here we assess the utility of acoustic SCR for estimating population density of owls, a group of birds for which population estimates are generally lacking. We conducted passive acoustic surveys for Barred Owls (Strix varia) and Great Horned Owls (Bubo virginianus) over the spring breeding seasons of 2020–2021 in a protected park in Georgia, USA. We used a combination of acoustic discrimination techniques to identify individuals, including spectrogram cross-correlation, hierarchical clustering, and visual scanning. The resulting estimates of the density of Great Horned Owl individuals (0.28 ± 0.026 [SE] per km2) were consistent with population density estimates from previous studies in other parts of the species' range. However, our methods appeared unsuitable for distinguishing Barred Owl individuals, which prevented estimation of population density for this species. We provide recommendations to improve acoustic sampling and individual discrimination of owls and suggest that acoustic SCR offers important advantages over conventional methods for monitoring some cryptic birds. Los métodos de captura-recaptura espacial (CRE) acústica parecen ser ideales para estimar las tendencias poblacionales de especies crípticas que son de difícil seguimiento. A pesar de la evidencia que sugiere que la CRE acústica ofrece mayor precisión que las estimaciones obtenidas mediante muestreo de distancia o enfoques de marcado-recaptura, ésta rara vez se ha aplicado a taxones aviares. Evaluamos la utilidad de la CRE acústica para estimar la densidad poblacional de búhos, un grupo de aves para el cual generalmente faltan estimaciones poblacionales. Realizamos estudios acústicos pasivos para Strix varia y Bubo virginianus durante las temporadas de cría en las primaveras del 2020 y 2021 en un parque protegido de Georgia, EEUU. Utilizamos una combinación de técnicas de discriminación acústica para identificar individuos, incluyendo correlación cruzada de espectrogramas, agrupacion jerárquica y escaneo visual. Las estimaciones resultantes de la densidad de individuos de B. virginianus (0.28 ± 0.026 [EE] por km2) fueron consistentes con las estimaciones de densidad poblacional obtenidas en estudios realizados previamente en otras áreas del rango de distribución de la especie. Sin embargo, nuestros métodos parecieron inadecuados para distinguir individuos de S. varia, lo que impidió la estimación de su densidad poblacional. Ofrecemos recomendaciones para mejorar el muestreo acústico y la discriminación individual de búhos, y sugerimos que la CRE acústica ofrece importantes ventajas sobre los métodos convencionales utilizados para el seguimiento de algunas aves crípticas. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

The south Florida subspecies of the Red-shouldered Hawk (Buteo lineatus extimus) is distinctly paler and smaller than other subspecies, reproduces at a lower rate, and can occupy very different habitats such as open marshes and grasslands with only scattered trees. We evaluated population differentiation between the south Florida population of Red-shouldered Hawks and two populations of eastern Red-shouldered Hawks (B. l. lineatus) in suburban (Cincinnati) and rural (Hocking Hills) environments in southern Ohio. Based on analysis of 11 microsatellite loci, we found significant genetic differentiation between the south Florida and eastern populations (FST = 0.077–0.097), as well as significant differentiation between the two populations of the eastern subspecies (FST = 0.047). Standardized genetic distance principal components analysis indicated two clusters, with individuals from the two Ohio populations forming a single cluster and those from Florida forming a second cluster. The substantial differences between the south Florida and other subspecies suggest this population warrants attention and possibly management as a distinct conservation unit, particularly in light of possible threats including habitat loss and rodenticide exposure. La subespecie del sur de Florida Buteo lineatus extimus es claramente más pálida y más pequeña que otras subespecies, se reproduce a un ritmo menor y puede ocupar hábitats muy diferentes, como marismas abiertas y pastizales con solo árboles dispersos. Evaluamos la diferenciación poblacional entre la población de B. l. extimus del sur de Florida y dos poblaciones orientales de B. l. lineatus de ambientes suburbanos (Cincinnati) y rurales (Hocking Hills) en el sur de Ohio. Con base en el análisis de 11 loci de microsatélites, encontramos una diferenciación genética significativa entre las poblaciones del sur de Florida y las orientales (FST = 0.077–0.097), así como una diferenciación significativa entre las dos poblaciones de la subespecie oriental (FST = 0.047). El análisis estandarizado de componentes principales de la distancia genética mostró dos grupos, con individuos de las dos poblaciones de Ohio formando un solo grupo y aquellos de Florida formando un segundo grupo. Las diferencias sustanciales entre el sur de Florida y otras subespecies sugieren que esta población merece atención y posiblemente manejo como una unidad de conservación distinta, particularmente a la luz de las posibles amenazas que incluyen la pérdida de hábitat y la exposición a rodenticidas. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

We studied the natural history of Gray Hawks (Buteo plagiatus) in the Lower Rio Grande Valley of Texas. We used GPS-GSM telemetry to quantify dispersal time and distance, winter home range size of juveniles, and home range size of adults. Home ranges were calculated using the kernel Brownian bridge home range estimator. The median dispersal date for 14 juvenile Gray Hawks was 11 August and they traveled a median straight-line distance of 453 km. Mean winter home range sizes for 11 juveniles was 707 ha. For juveniles, female winter home ranges were larger than those of males, and juvenile winter home ranges were larger in natural than in urban areas. Mean 95% home range sizes for 20 adult Gray Hawks was 530 ha. Mean adult male home range size was larger in natural than in urban areas. Adult Gray Hawks remained in their home ranges year-round. Estudiamos la historia natural de Buteo plagiatus en el Valle Inferior del Río Grande de Texas. Utilizamos telemetría GPS-GSM para cuantificar el tiempo y la distancia de dispersión, el tamaño del área de campeo de los juveniles en invierno y el tamaño del área de campeo de los adultos. Las áreas de campeo se calcularon utilizando el estimador de puentes brownianos del método kernel. La fecha mediana de dispersión de 14 juveniles de B. plagiatus fue el 11 de agosto y recorrieron una distancia mediana en línea recta de 453 km. El tamaño medio del área de campeo de invierno para 11 juveniles fue de 707 ha. Considerando los juveniles, las áreas de campeo de invierno de las hembras fueron más grandes que las de los machos, y las áreas de campeo de invierno de los juveniles fueron más grandes en las áreas naturales que en las urbanas. El tamaño medio del 95% del área de campeo para 22 adultos de B. plagiatus fue de 526 ha. El tamaño promedio del área de campeo de los machos adultos fue mayor en las áreas naturales que en las urbanas. Los adultos de B. plagiatus permanecieron en sus áreas de campeo durante todo el año. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Divergent life histories by sex are common within species of birds; thus, the ability to accurately determine sex is essential in many studies of avian ecology and can possibly lead to more effective conservation strategies. However, sex determination can be difficult in species not displaying dimorphic plumage, including most raptors, and size dimorphism has limited use during observations but is promising for determining sex of raptors in hand. The Broad-winged Hawk (Buteo platypterus), known for its long-distance migrations between North and South America, has yet to be examined for morphometric variation across its wide range. We analyzed body mass, wing chord, and tail length data for 119 adult Broad-winged Hawks captured in eastern North America during the breeding seasons from 1974 to 2020. We found that adult female Broad-winged Hawks were larger than adult males overall. Hawks from Wisconsin were larger than hawks from Pennsylvania and Maryland, and hawks from Ontario were larger than those from other populations, suggesting geographic variation in size. Using linear discriminant analysis, we showed that it was possible to determine sex of adults with 99% accuracy in Wisconsin populations using only body mass as a predictor, and 100% accuracy in Pennsylvania and Maryland populations using body mass, wing chord, and tail length as predictors. Morphometric measurements combined with discriminant function analysis proved useful in discerning sex of breeding-season Broad-winged Hawks, and results of this study can guide researchers working in similar regions. We encourage researchers to collect body measurements for this species and other monomorphic raptors to further inform sex determination. Las historias de vida divergentes según el sexo son comunes en aves, por lo que la capacidad de determinar con precisión el sexo es esencial en muchos estudios de ecología aviar y posiblemente puede conducir a estrategias de conservación más efectivas. Sin embargo, la determinación del sexo puede ser difícil en especies que no muestran dimorfismo de plumaje, incluida la mayoría de las aves rapaces, y el dimorfismo de tamaño tiene un uso limitado durante las observaciones, pero es prometedor para determinar el sexo de las aves rapaces en la mano. Buteo platypterus, conocido por sus migraciones de larga distancia entre América del Norte y América del Sur, aún debe ser estudiado para determinar la variación morfométrica a lo largo de su amplia área de distribución. Analizamos los datos de masa corporal, cuerda alar y longitud de la cola de 119 individuos de B. platypterus capturados en el este de América del Norte durante las temporadas reproductivas de 1974 a 2020. Encontramos que, en general, las hembras adultas de B. platypterus eran más grandes que los machos adultos. Los individuos de Wisconsin eran más grandes que los de Pensilvania y Maryland, y los individuos de Ontario eran más grandes que los de otras poblaciones, lo que sugiere una variación geográfica en tamaño. Usando un análisis discriminante lineal, mostramos que era posible determinar el sexo de los adultos con un 99% de precisión en las poblaciones de Wisconsin usando solo la masa corporal como predictor, y con un 100% de precisión en las poblaciones de Pensilvania y Maryland usando la masa corporal, la cuerda alar y la longitud de la cola como predictores. Las mediciones morfométricas combinadas con análisis de función discriminante demostraron ser útiles para discernir el sexo de B. platypterus en la temporada reproductiva, y los resultados de este estudio pueden guiar a los investigadores que trabajan en regiones similares. Alentamos a los investigadores a recopilar medidas corporales de esta especie y de otras rapaces monomórficas para avanzar en la determinación del sexo. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

The Broad-winged Hawk (Buteo platypterus) is one of the most easily observed North American raptors during migration, yet little is known about its distribution during the nonbreeding season. To better understand the winter distribution of Broad-winged Hawks by age, we compiled 2164 Broad-winged Hawk sightings with age data and 25,797 sightings without age data reported to eBird during the nonbreeding period from 2000–2020. The mean latitude of adult birds was significantly farther south than the mean latitude of immatures, with broad overlap in the distribution of both age classes from the United States through South America. The distribution of birds that were not aged overlapped the distribution of both age classes. A higher proportion of immatures was observed in the United States through Central America, with a mean latitude of 15.69°N, whereas adults were concentrated in Central and South America (with a mean latitude of 9.93°N). When only birds wintering south of the United States were analyzed, immatures were still found farther north than adults, although the latitude difference was less. The winter age class distribution for Broad-winged Hawks could result from short-stopping behavior occurring more often in immatures than adults. Further research is needed to understand how geographic, sex, and age class groups may differ in winter distributions and the implications of these patterns. Citizen science data from eBird proved useful in examining broad-scale patterns in Broad-winged Hawk winter distribution and is a valuable resource to scientists evaluating avian distributions. Buteo platypterus es una de las rapaces norteamericanas más fáciles de observar durante la migración, pero se sabe poco sobre su distribución durante la temporada no reproductiva. Para comprender mejor la distribución invernal por edad de esta especie, recopilamos 2164 avistamientos de B. platypterus con datos de edad y 25,797 avistamientos sin datos de edad reportados a eBird durante el período no reproductivo de 2000–2020. La latitud media de las aves adultas se ubicó significativamente más al sur que la latitud media de las aves inmaduras, con una amplia superposición en la distribución de ambas clases de edad desde los Estados Unidos hasta América del Sur. La distribución de las aves sin datos de edad se superpuso con la distribución de ambas clases de edad. Se observó una mayor proporción de inmaduros en Estados Unidos y a lo largo de América Central, con una latitud media de 15.69°N, mientras que los adultos se concentraron en América Central y del Sur (con una latitud media de 9.93°N). Cuando solo se analizaron las aves que invernaban al sur de los Estados Unidos, los inmaduros aún se encontraron más al norte que los adultos, aunque la diferencia de latitud fue menor. La distribución de clases de edad durante el invierno para B. platypterus podría deberse a un comportamiento de parada corta que ocurre con más frecuencia en los inmaduros que en los adultos. Se necesita más investigación para comprender cómo los grupos geográficos, de sexo y de clase de edad pueden diferir en las distribuciones de invierno y las implicaciones de estos patrones. Los datos de ciencia ciudadana de eBird demostraron ser útiles para examinar patrones a gran escala en la distribución invernal de B. platypterus y son un recurso valioso para los científicos que evalúan las distribuciones de las aves. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

Interspecific competition occurs when two sympatric species utilize the same limited supply of a basic resource, such as food; the degree of diet overlap is an essential metric for examining potential competition between the species. The Long-legged Buzzard (Buteo rufinus) is a relative newcomer to the island of Cyprus, where it is sympatric with the larger Bonelli's Eagle (Aquila fasciata), a potential competitor for both food and space (nesting territories). We studied the diet of the Long-legged Buzzard in the 2005, 2006, and 2018 nesting seasons through analysis of pellets and prey remains collected at 38 sites. The most abundant prey class was mammals (68.8% frequency, 58.9% biomass), followed by reptiles (16.8% frequency, 36.3% biomass), and birds (4.3% frequency, 4.6% biomass). The most numerous prey species were black rats (Rattus rattus), starred agamas (Stellagama stelio), house mice (Mus musculus), and large whip snakes (Dolichophis jugularis), but in terms of biomass, the most important prey items were black rats, large whip snakes, long-eared hedgehogs (Hemiechinus auritus dorotheae), and starred agamas. We compared the diet of the Long-legged Buzzard to that of the Bonelli's Eagle, whose diet was dominated by birds (62.1% frequency, 76.1% biomass) and to a lesser degree by mammals (29.5% frequency, 21.9% biomass). The mean prey biomass for the Long-legged Buzzard was estimated as 167 g, compared to 350 g for the Bonelli's Eagle; this difference reflected the almost two-fold difference in mass between females of the two species. Diet overlap measured with Pianka's index was <0.5, suggesting an intermediate niche overlap mainly due to utilization of an abundant prey resource, such as the black rat. Niche breadth for the Long-legged Buzzard measured using Levins' index ranged from 0.485 in 2005 to 0.081 in 2018. This decrease in niche breadth over time in a generalist species can occur when there is a superabundance of a particular prey. The mean Levins' index for the Bonelli's Eagle was also low, 0.271 (1999–2001). Based on the diet comparison, we concluded that there was no evidence for interspecific competition in terms of food. La competencia interespecífica ocurre cuando dos especies simpátricas utilizan el mismo suministro limitado de un recurso básico, como por ejemplo la comida; el grado de solapamiento de la dieta es una métrica esencial para examinar la competencia potencial entre las especies. Buteo rufinus es una especie relativamente nueva en la isla de Chipre, donde se presenta en simpatría con Aquila fasciata, de mayor tamaño, un competidor potencial tanto por comida como por espacio (territorios de nidificación). Estudiamos la dieta de B. rufinus en las temporadas de cría de 2005, 2006 y 2018 mediante el análisis de egagrópilas y restos de presas recolectados en 38 sitios. Las presas más abundantes fueron los mamíferos (68,8% de frecuencia, 58,9% de biomasa), seguido de los reptiles (16,8% de frecuencia, 36,3% de biomasa) y las aves (4,3% de frecuencia, 4,6% de biomasa). Las especies de presa más numerosas fueron Rattus rattus, Stellagama stelio, Mus musculus y Dolichophis jugularis, si bien en términos de biomasa las presas más importantes fueron R. rattus, D. jugularis, Hemiechinus auritus dorotheae y S. stelio. Comparamos la dieta de B. rufinus con la de A. fasciata, cuya dieta estaba dominada por aves (62,1% de frecuencia, 76,1% de biomasa) y en menor medida por mamíferos (29,5% de frecuencia, 21,9% de biomasa). La biomasa de la presa promedio para B. rufinus se estimó en 167 g, en comparación con 350 g para A. fasciata; esta disparidad reflejó la diferencia de masa de casi el doble entre las hembras de las dos especies. El solapamiento de dieta medido con el índice de Pianka fue <0,5, lo que sugiere un solapamiento de nicho intermedio debido principalmente a la utilización de un recurso de presa abundante como R. rattus. La amplitud de nicho para B. rufinus, medido con el índice de Levins, fluctuó entre 0,485 en 2005 y 0,081 en 2018. Esta disminución en la amplitud de nicho a lo largo del tiempo en una especie generalista puede ocurrir cuando hay una sobreabundancia de una presa en particular. El índice de Levins medio para A. fasciata también fue bajo, 0,271 (1999–2001). Basados en la comparación de la dieta, concluimos que no hubo evidencia de competencia interespecífica en términos de alimentación. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

The strategies that migratory raptors adopt during migration reveal their long-term adaptations to different environments along their migration routes and of their stopover sites. We recorded the daily departure time of Chinese Sparrowhawks (Accipiter soloensis) and Gray-faced Buzzards (Butastur indicus) during their southward migration in autumn 2019 at Kenting National Park, southern Taiwan, and 2020 in Yushan National Park, central Taiwan. At both watchsites, Gray-faced Buzzards started their migration journey about 1 hr earlier than Chinese Sparrowhawks. After adjusting for the local sunrise time, the first daily appearance time of Gray-faced Buzzards (–2.5 ± 9.3 min) was significantly earlier than that of Chinese Sparrowhawks (47.0 ± 29.3 min) by about 50 min at Kenting National Park. Though they initiated migration later in morning at montane stopover sites in Yushan National Park, the same trend was observed and with even greater difference, about 70 min. These results indicate that these two species migrate in different daily periods and suggest that Chinese Sparrowhawks might choose to exploit stronger thermal uplifts in September before leaving the island, as they started migration later in the morning. In contrast, Gray-faced Buzzards, a species more dependent on soaring-gliding flight, set off earlier in the day, probably to take advantage of stronger northeastern tailwinds that begin in October. We conclude that the prevailing monthly wind conditions, particularly influenced by the northeast monsoons, shape the different diurnal migration times of these two raptors migrating along the East-Asian Oceanic Flyway. Las estrategias que adoptan las rapaces migratorias durante la migración revelan sus adaptaciones a largo plazo a diferentes ambientes a lo largo de sus rutas migratorias y de sus sitios de parada. Registramos la hora de partida diaria de Accipiter soloensis y Butastur indicus durante su migración hacia el sur en el otoño de 2019 en el Parque Nacional Kenting, en el sur de Taiwán, y en 2020 en el Parque Nacional Yushan, en el centro de Taiwán. En ambos sitios de observación, B. indicus comenzó su migración aproximadamente 1 hora antes que A. soloensis. Después de ajustar por la hora local del amanecer, el primer horario diario de aparición de B. indicus (–2,5 ± 9,3 min) fue significativamente más temprano que el de A. soloensis (47,0 ± 29,3 min) por unos 50 min en Kenting. Aunque iniciaron la migración más tarde en la mañana en los sitios montanos de parada en Yushan, se observó la misma tendencia y con una diferencia aún mayor, alrededor de 70 min. Estos resultados indican que estas dos especies migran en diferentes períodos diarios y sugieren que A. soloensis podría optar por explotar corrientes térmicas ascendentes más fuertes en septiembre antes de abandonar la isla, ya que comenzó a migrar más tarde en la mañana. Por el contrario, B. indicus, una especie que depende más del vuelo planeado, partió más temprano en el día, probablemente para aprovechar los fuertes vientos de cola del noreste que comienzan en octubre. Concluimos que las condiciones mensuales predominantes de viento, particularmente influenciadas por los monzones del noreste, moldean los diferentes horarios migratorios diurnos de estas dos rapaces que migran a lo largo de la ruta migratoria oceánica del este de Asia. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

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The south Florida subspecies of the Red-shouldered Hawk (Buteo lineatus extimus) is distinctly paler and smaller than other subspecies, reproduces at a lower rate, and can occupy very different habitats such as open marshes and grasslands with only scattered trees. We evaluated population differentiation between the south Florida population of Red-shouldered Hawks and two populations of eastern Red-shouldered Hawks (B. l. lineatus) in suburban (Cincinnati) and rural (Hocking Hills) environments in southern Ohio. Based on analysis of 11 microsatellite loci, we found significant genetic differentiation between the south Florida and eastern populations (FST = 0.077–0.097), as well as significant differentiation between the two populations of the eastern subspecies (FST = 0.047). Standardized genetic distance principal components analysis indicated two clusters, with individuals from the two Ohio populations forming a single cluster and those from Florida forming a second cluster. The substantial differences between the south Florida and other subspecies suggest this population warrants attention and possibly management as a distinct conservation unit, particularly in light of possible threats including habitat loss and rodenticide exposure. La subespecie del sur de Florida Buteo lineatus extimus es claramente más pálida y más pequeña que otras subespecies, se reproduce a un ritmo menor y puede ocupar hábitats muy diferentes, como marismas abiertas y pastizales con solo árboles dispersos. Evaluamos la diferenciación poblacional entre la población de B. l. extimus del sur de Florida y dos poblaciones orientales de B. l. lineatus de ambientes suburbanos (Cincinnati) y rurales (Hocking Hills) en el sur de Ohio. Con base en el análisis de 11 loci de microsatélites, encontramos una diferenciación genética significativa entre las poblaciones del sur de Florida y las orientales (FST = 0.077–0.097), así como una diferenciación significativa entre las dos poblaciones de la subespecie oriental (FST = 0.047). El análisis estandarizado de componentes principales de la distancia genética mostró dos grupos, con individuos de las dos poblaciones de Ohio formando un solo grupo y aquellos de Florida formando un segundo grupo. Las diferencias sustanciales entre el sur de Florida y otras subespecies sugieren que esta población merece atención y posiblemente manejo como una unidad de conservación distinta, particularmente a la luz de las posibles amenazas que incluyen la pérdida de hábitat y la exposición a rodenticidas. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

The south Florida subspecies of the Red-shouldered Hawk (Buteo lineatus extimus) is distinctly paler and smaller than other subspecies, reproduces at a lower rate, and can occupy very different habitats such as open marshes and grasslands with only scattered trees. We evaluated population differentiation between the south Florida population of Red-shouldered Hawks and two populations of eastern Red-shouldered Hawks (B. l. lineatus) in suburban (Cincinnati) and rural (Hocking Hills) environments in southern Ohio. Based on analysis of 11 microsatellite loci, we found significant genetic differentiation between the south Florida and eastern populations (FST = 0.077–0.097), as well as significant differentiation between the two populations of the eastern subspecies (FST = 0.047). Standardized genetic distance principal components analysis indicated two clusters, with individuals from the two Ohio populations forming a single cluster and those from Florida forming a second cluster. The substantial differences between the south Florida and other subspecies suggest this population warrants attention and possibly management as a distinct conservation unit, particularly in light of possible threats including habitat loss and rodenticide exposure. La subespecie del sur de Florida Buteo lineatus extimus es claramente más pálida y más pequeña que otras subespecies, se reproduce a un ritmo menor y puede ocupar hábitats muy diferentes, como marismas abiertas y pastizales con solo árboles dispersos. Evaluamos la diferenciación poblacional entre la población de B. l. extimus del sur de Florida y dos poblaciones orientales de B. l. lineatus de ambientes suburbanos (Cincinnati) y rurales (Hocking Hills) en el sur de Ohio. Con base en el análisis de 11 loci de microsatélites, encontramos una diferenciación genética significativa entre las poblaciones del sur de Florida y las orientales (FST = 0.077–0.097), así como una diferenciación significativa entre las dos poblaciones de la subespecie oriental (FST = 0.047). El análisis estandarizado de componentes principales de la distancia genética mostró dos grupos, con individuos de las dos poblaciones de Ohio formando un solo grupo y aquellos de Florida formando un segundo grupo. Las diferencias sustanciales entre el sur de Florida y otras subespecies sugieren que esta población merece atención y posiblemente manejo como una unidad de conservación distinta, particularmente a la luz de las posibles amenazas que incluyen la pérdida de hábitat y la exposición a rodenticidas. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

Raptor polymorphisms have played an important role in understanding how evolutionary forces within and between populations operate. However, within a population little is known about the history of the polymorphism, the effects of any population bottlenecks, and the overall stability of the polymorphism. We investigated the stability of a melanin-based color polymorphism in Swainson's Hawks (Buteo swainsoni) in California over a 100-year period. In the mid-20th century Swainson's Hawks in California declined by 90%. Therefore, we examined the morphs of breeding individuals collected before 1950 and compared them to images from eBird taken between 2008–2019 and from a Google Images search, because a disproportionate survival of rare alleles after a population bottleneck could lead to changes in current clines. Between the two periods, we did not find differences in plumage morphs, nor did we find evidence of latitude or longitudinal clines over this relatively small spatial scale. Thus, despite a large population decline, this polymorphism has remained consistent over time. Our results suggest that the relatively high occurrence of dark morphs in this population is not simply a result of a bottleneck. Los polimorfismos observados en aves rapaces han jugado un papel importante en la comprensión de cómo operan las fuerzas evolutivas dentro y entre las poblaciones. Sin embargo, dentro de una población se sabe poco sobre la historia del polimorfismo, los efectos de los cuellos de botella poblacionales y la estabilidad general del polimorfismo. Investigamos la estabilidad de un polimorfismo de color dependiente de la presencia de melanina en Buteo swainsoni en California durante un período de 100 años. A mediados del siglo XX, los individuos de B. swainsoni en California se redujeron en un 90%. Por lo tanto, examinamos las morfologías de individuos reproductores recolectados antes de 1950 y las comparamos con imágenes de eBird tomadas entre 2008 y 2019 y de aquellas encontradas en Google, dado que una supervivencia desproporcionada de alelos raros después de un cuello de botella poblacional podría conducir a cambios en las clinas actuales. Entre los dos períodos, no encontramos diferencias en los morfos del plumaje, ni encontramos evidencia de clinas latitudinales o longitudinales a lo largo de esta escala espacial relativamente pequeña. Por lo tanto, a pesar de una gran disminución poblacional, este polimorfismo se ha mantenido constante a lo largo del tiempo. Nuestros resultados sugieren que la aparición relativamente alta de morfos oscuros en esta población no es simplemente el resultado de un cuello de botella. [Traducción del equipo editorial] [ABSTRACT FROM AUTHOR]

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Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With a breeding range extending from approximately 68°N in northern Canada to 8°N in Panama, Red-tailed Hawks ( Buteo jamaicensis) exhibit migrations that vary substantially with latitude. Northern populations are almost completely migratory, middle-latitude populations are partially migratory, and southern populations south of 38°N are considered sedentary. Contrary to the latter widely held belief, we found that many juveniles and young adults from one population below 38°N are also partially migratory. However, unlike most birds in the northern hemisphere that migrate south in autumn, young Red-tailed Hawks from our southwestern California study area migrated north in summer to summering areas as far as 1462 km from their natal nests. Of the 5271 Red-tailed Hawk nestlings we banded in the study area and an additional 189 banded by other researchers, 205 were encountered (found dead or alive or recaptured) outside the study area. We classified 64 encountered hawks as potential migrants, most (69%) of which were encountered to the north of their natal nest (median = 383 km). We found that juveniles and young adults banded south of 35°N in the Pacific Flyway migrated north, whereas those banded north of 40°N migrated south. Sixteen hawks from the study area equipped with satellite transmitters as fledglings migrated north (range 342-24°) in summer, up to 1388 km, and returned to their natal region in autumn of the same year. This pattern was repeated annually until they acquired a mate and territory. Our results showed that many or most young Red-tailed Hawks migrate northward in the summer, and we propose that this pattern may be a response to historical climate changes, seasonal changes in sciurid prey availability, and/or dominance of territorial adults. Con una distribución reproductiva que se extiende aproximadamente desde los 68°N en el norte de Canadá hasta los 8°N en el sur de Panamá, Buteo jamaicensis presenta patrones migratorios que varían substancialmente con la latitud. Las poblaciones septentrionales son casi por completo migratorias, las poblaciones de latitudes medias son parcialmente migratorias y las poblaciones meridionales, al sur de los 38°N, son consideradas sedentarias. Contrariamente a esto último, que está ampliamente aceptado, encontramos que muchos individuos juveniles y adultos jóvenes de una población ubicada por debajo de los 38°N son también migrantes parciales. Sin embargo, a diferencia de la mayoría de las aves en el Hemisferio Norte que migran hacia el sur en otoño, los individuos jóvenes de B. jamaicensis de nuestra área de estudio ubicada al suroeste de California migraron hacia el norte en verano, a áreas de veraneo ubicadas a distancias tan alejadas como 1462 km de sus áreas natales. De los 5271 individuos de B. jamaicensis que anillamos en el área de estudio y de los 189 individuos de la misma especie anillados por otros investigadores, 205 fueron encontrados (muertos, vivos o recapturados) fuera del área de estudio. Clasificamos 64 individuos como migrantes potenciales, la mayoría (69%) de los cuales fueron hallados al norte de sus áreas natales (mediana = 383 km). Encontramos que los individuos juveniles y adultos jóvenes anillados al sur de los 35°N en la vía migratoria del Pacífico migraron hacia el norte, mientras que aquellos individuos anillados al norte de los 40°N migraron hacia el sur. Dieciséis individuos del área de estudio que fueron equipados con transmisores satelitales cuando eran volantones migraron hacia el norte (rango 342-24°) en verano, recorriendo hasta 1388 km, y regresaron a sus regiones natales en el otoño del mismo año. Este patrón se repitió anualmente hasta que estos individuos consiguieron pareja y territorio. Nuestros resultados muestran que muchos o la mayoría de los individuos jóvenes de B. jamaicensis migraron hacia el norte en verano. Proponemos que este patrón puede ocurrir en respuesta a cambios climáticos históricos, a cambios estacionales en la disponibilidad de presas de esciúridos y/o a la dominancia de adultos territoriales. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Raptor Research is the property of Raptor Research Foundation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)