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Restoring Aplomado Falcons to the United States
Abstract and Figures
DEVOLVIENDO A FALCO FEMORALIS A LOS ESTADOS UNIDOS Se liberaron volantones de Falco femoralis criados en cautiverio a lo largo de las planicies costeras del sur de Texas (839 aves de 21 sitios durante 1993–2004) y en el desierto de Chihuahua del oeste de Texas (637 aves de 11 sitios durante 2002–2011) y del sur de Nuevo México (337 aves de 10 sitios durante 2006–2012). Las liberaciones en la costa de Texas produjeron dos poblaciones que anidaron: 15–18 pares cerca de Brownsville y 15 pares en dos islas cerca de Rockport. El hábitat de esta área se compone de una extensa sabana abierta, lo que representa la condición ancestral de casi toda la región. Actualmente se encuentra casi completamente dominada por tierras de labranza y matorrales; este último alberga a Bubo virginianus, uno de los mayores depredadores de halcones. Por el contrario, las liberaciones en el desierto de Chihuahua no fueron exitosas en el establecimiento de poblaciones silvestres. Aunque se encontraron 8–10 pares en el oeste de Texas en 2009, para el 2011 sólo se registró un par y no se encontró ninguno en 2012, como consecuencia aparente de una sequía severa. Una sola pareja documentada en Nuevo México en 2011 estuvo asociada con la alimentación artificial de aves de presa. Concluimos que la conservación y la expansión de poblaciones de F. femoralis en las planicies costeras de Texas requerirán de la protección y el manejo de los territorios de cría existentes, y de la creación y manejo de sabanas libres de matorrales. La sequía persistente, la reducción de las poblaciones de presas y las altas tasas de mortalidad debidas a la depredación por parte de rapaces parecen impedir el restablecimiento de poblaciones de F. femoralis en el oeste de Texas o Nuevo México.
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... Historically, this subspecies was a year-round resident of the southwestern United States (Ligon, 1961;Hector, 1987) and northern Mexico south to Belize and Guatemala, but was extirpated in the United States by the 1950s (Kiff and Peakall, 1980). Causes of population declines are uncertain but are thought to have resulted from the conversion of open grasslands to agriculture and brushlands, leading to increased predator populations and suppressed fire regimes (Hunt et al., 2013). Releases of captive-reared individuals into coastal South Texas began in 1985 but failed to reestablish the population until additional releases occurred during 1993-2004. ...
... Releases of captive-reared individuals into coastal South Texas began in 1985 but failed to reestablish the population until additional releases occurred during 1993-2004. The population has appeared stable at roughly 35 pairs since the bulk of releases ceased in 2004 (Jenny et al., 2004;Hunt et al., 2013;McClure et al., 2017a). The Peregrine Fund has been intensively monitoring the population since 1993. ...
... Habitat at Matagorda Island included gulf cordgrass, marsh hay cordgrass (S. patens), gulf dune paspalum (Paspalum monostachyum), and gulf bluestem (Schizachyrium maritimum). Aplomado Falcons reuse nests built by other large birds and establish nests in wild vegetation including tree-yucca (principally Yucca treculeana), honey mesquite (Prosopis glandulosa), spiny hackberry (Celtis ehrenbergiana), along with other species of vegetation (summarized by Hunt et al., 2013). The falcons often also nest in suitable human-constructed artificial nest structures (Hunt et al., 2013). ...
We examined long-term demography of an endangered subspecies, the Northern Aplomado Falcon (Falco femoralis septentrionalis), in South Texas, USA. The population has been managed and monitored since reintroductions began in 1993. Data spanning 1993–2018 enabled us to build an integrated population model (IPM) and a Cormack-Jolly-Seber model to estimate survival for three life stages (first-year, non-breeders, and breeders) and both sexes, abundance of males, fecundity, immigration, and emigration. Male falcons survived at lower rates than females during their first year; Hurricane Harvey caused a decline in survival rates of first-years and breeders; and fecundity increased after 2011 coinciding with changes in management focused on improving nest platforms and habitat quality. Both immigration of non-breeders and emigration were likely negligible for this population suggesting a potentially isolated population. The IPM likely overestimated immigration of breeders warranting further research. Population growth rates were greatest during years having more released captive-reared young and greater probabilities of breeder survival. Importantly, an apparent decrease in breeder survival of unknown cause occurred during 2006 to 2009 when breeder survival declined and remained low for several years. Our ability to identify the cause for reduced survival is now greatly hampered by the extended time that has passed, limiting the usefulness of our recent awareness of reduced survival for informing management and further highlighting the importance of real-time monitoring for proactive decision making processes. Our study greatly improves knowledge of demographics for a reintroduced, isolated, and intensively managed population of Aplomado Falcons. Applying this IPM to new data each year will enable adaptive management of the South Texas population by providing annual evaluations of vital rates along with revised assessments of monitoring and management.
... The current conservation status of the Aplomado Falcon in the Chihuahuan Desert is nebulous. Aplomado Falcons of unknown origin were observed in New Mexico and west Texas before and after the decade-long reintroduction program (2002( -2012( , Hunt et al. 2013, and in Chihuahua and San Luis Potosí after 2009 (eBird 2020). Almost no recruitment of Aplomado Falcons in the Chihuahuan Desert has been documented outside the central Chihuahua population, with the exception of a few successful nesting attempts by captive-raised birds (Hunt et al. 2013) and by wild birds (Meyers andWilliams 2005, USFWS 2014). ...
... Aplomado Falcons of unknown origin were observed in New Mexico and west Texas before and after the decade-long reintroduction program (2002( -2012( , Hunt et al. 2013, and in Chihuahua and San Luis Potosí after 2009 (eBird 2020). Almost no recruitment of Aplomado Falcons in the Chihuahuan Desert has been documented outside the central Chihuahua population, with the exception of a few successful nesting attempts by captive-raised birds (Hunt et al. 2013) and by wild birds (Meyers andWilliams 2005, USFWS 2014). Aplomado Falcons probably nest in other parts of the Chihuahuan Desert that have not been surveyed during the breeding season. ...
... Determining availability of suitable habitat for the Aplomado Falcon elsewhere in the Chihuahuan Desert has been difficult. For instance, reintroductions of captive-bred falcons to potential breeding habitat failed to establish breeding territories in the Chihuahuan Desert grasslands of New Mexico and west Texas (Hunt et al. 2013). In addition, several authors have retrospectively identified breeding habitat in Chihuahua, Mexico, and New Mexico and west Texas, USA (Young et al. 2002, Zamarron Rodríguez 2003, Lanser 2003, Rodríguez Salazar 2004, Swiekert and Phillips 2015 and the rest of Mexico (Keddy- Hector et al. 2014) using satellite imagery. ...
The persistence of a species throughout its geographic range requires dispersal among its populations. The study of dispersal is particularly relevant for species whose geographic range has contracted, such as the endangered Northern Aplomado Falcon (Falco femoralis septentrionalis). We used Argos 5-g PTT-100 satellite transmitters to determine the movements of two wild Chihuahuan Desert Aplomado Falcons (one female and one male) from fledging to breeding (male), or transmitter failure (female), at 1062 d and 439 d of age, respectively. Both falcons dispersed from their natal territories 2-3 mo after fledging. These falcons then wandered between activity centers near historic breeding territories and some territories recently converted to farmlands. These two falcons also explored areas outside known breeding areas via some long-distance movements to areas of potential breeding habitat being converted to farmland. In 2 yr, movements of the male covered 7412 sq. km. This falcon nested unsuccessfully with an unbanded female in a vacant breeding territory 15 km from his natal site. His nesting attempt the following year yielded two fledglings. While a breeding bird, the male falcon had a home range of 200 sq. km. For 17 mo, the female falcon wandered through an area of 12,136 sq. km. The farthest distance she traveled from her nest site prior to transmitter failure was 154 km.
... The subspecies has declined significantly in abundance over the past century, with the last breeding pair in the USA (prior to captive release efforts initiated in the mid-1980s) observed in the wild in 1952 (Hunt et al. 2013). Although the species' overall geographic distribution extends south through Mexico to Argentina, the distribution of the most northern subspecies (F. ...
... The captive population was created with the intention to propagate and release captive-hatched individuals in an effort to restore the species to its original range within the southern USA. The first captive-hatched Aplomado Falcons were produced in 1982 (Cade et al. 1991) and the first were released to the wild in 1985 (Hunt et al. 2013). All released Aplomado Falcons were offspring of the 27 founders or their subsequent generations that were reared and bred in captivity. ...
... Although substantial effort was made in an attempt to establish a breeding population in West Texas and New Mexico, only one nesting pair was observed in New Mexico after 2012 despite the release of 637 captive-hatched Aplomado Falcons in West Texas between 2002 and 2011, and more than 337 in New Mexico between 2006 and 2012 (Hunt et al. 2013, USFWS 2014. The exact reason the released Aplomado Falcons failed to establish is not fully known, but multiple years of severe drought and deterioration of ground cover likely decreased prey availability, which in turn likely decreased the population's productivity during the reintroduction efforts (Hunt et al. 2013, Sweikert andPhillips 2015). ...
Reintroductions are an important tool in conservation for preserving and enhancing biodiversity and preventing extinction, and post-release monitoring is essential to evaluate and inform conservation management and maximize recovery success. By quantifying genetic diversity levels and effective population size (Ne) over time, managers can gauge to what degree additional efforts are needed to increase the likelihood of population persistence. The endangered Northern Aplomado Falcon (Falco femoralis septentrionalis) population in South Texas was reestablished and supplemented with captive-bred individuals originating from 27 founders collected in eastern Mexico (San Luis Potosí, Veracruz, Tabasco, and Chiapas). A total of 927 Aplomado Falcons were released at 23 locations along the southern coast of Texas between 1985 and 2004, and in 2012 and 2013. To assess the species' reintroduction and recovery, we applied a genetic monitoring approach using sampled nestlings (n = 267) from a total of 108 nests in 2004–2005 and 2012–2016. Based on ten microsatellite loci, levels of genetic diversity (i.e., allelic richness and heterozygosity) remained stable over the sampled time period, with no indication of inbreeding. Diversity levels were comparable to a subset of samples collected from the captive population founders (n = 11). Similarly, individuals from the South Texas population showed strong admixture with the founding population, and levels of both Ne and of effective breeding (Nb) showed no signs of decline over the sampled time period. To what degree overlapping generations and the release of additional Aplomado Falcons during the sampled time period limited our assessment of the South Texas population is not fully known. Continued monitoring across multiple generations is advisable to assess the population's ability to persist.
... Whooping cranes that utilize ANWR tend to not be observed in areas of dense live oak woodland and shrubland (Golden et al. 2022). Continuous prescribed burns help set back vegetation to early successional stages and lower overall plant height as whooping cranes prefer unobstructed views that allow for predator detection (Armbruster 1990), roosting, and foraging (Lewis 1995) as do Aplomado falcons for hunting prey and breeding, particularly on Matagorda Island (Perez et al. 1996;Macías-Duarte et al. 2004;Hunt et al. 2013). Using LANDFIRE intervals to guide prescribed burning may be detrimental to whooping crane management, and it is likely that the open habitat critical to both whooping cranes and Aplomado falcons use of the refuge would be lost to woody plant encroachment. ...
Background
The southeastern United States consists of diverse ecosystems, many of which are fire-dependent. Fires were common during pre-European times, and many were anthropogenic in origin. Understanding how prescribed burning practices in use today compare to historic fire regimes can provide perspective and context on the role of fire in critical ecosystems. On the Aransas National Wildlife Refuge (ANWR), prescribed burning is conducted to prevent live oak ( Quercus fusiformis ) encroachment and preserve the openness of the herbaceous wetlands and grasslands for endangered whooping cranes ( Grus americana ) and Aplomado falcons ( Falco femoralis ). This field note builds a digital fire atlas of recent prescribed burning on the refuge and compares it to the historical fire ecology of ANWR.
Results
Findings indicate that the refuge is maintaining fire-dependent ecosystems with an extensive burn program that includes a fire return interval between 2 and 10 years on a majority of the refuge, with some locations experiencing much longer intervals. These fire return intervals are much shorter than the historic burn regime according to LANDFIRE.
Conclusions
Following the fire return intervals projected by LANDFIRE, which project longer intervals than the prescribed fire program, would likely be detrimental to endangered species management by allowing increased woody plant encroachment and loss of open habitat important to whooping cranes and Aplomado falcons. Since prescribed fire is part of the management objectives on many national wildlife refuges in the United States, quantifying recent and historical fire ecology can provide useful insights into future management efforts, particularly in cases where endangered species are of special concern and management efforts may be counter to historical disturbance regimes.
... The Northern Aplomado Falcon (Falco femoralis septentrionalis), hereafter Aplomado Falcon, declined before ultimately disappearing from the United States in the 1950's, likely from a combination of habitat loss and indiscriminate use of the pesticides dichlorodiphenyltrichloroethane (DDT) and dieldrin (Hunt et al., 2013). Habitat changes in the Aplomado Falcon's range in Texas also contributed to the declines of other prairie and grassland dwelling species, including the Attwater's Prairie Chicken (Tympnuchus cupido attwateri) and Pronghorn (Antilocapra americana) (Lehmann, 1941;Simpson, Harveson, Brewer, Walser, & Sides, 2007). ...
... However, the four reintroduced populations are exhibiting very different trajectories, despite being established using the same suite of management techniques. Although this is not unique in small falcon recovery programmes, as shown by the mixed success with the reintroduction of the Aplomado Falcon Falco femoralis in south and west Texas (USA) (Hunt et al. 2013), our long-term monitoring programme allowed us comprehensively to explore the reasons behind these different trajectories. ...
Conservation translocations are commonly used in recovery programmes for threatened species from a wide range of taxa, but outcomes can vary considerably both within and between programmes, and the causes of success or failure are often unclear. Central to understanding translocation success is the implementation of an accompanying monitoring programme, enabling the drivers of population establishment and persistence to be explored within a population ecology framework. Here we review and assess the outcome of a translocation programme for the Endangered Mauritius Kestrel, which involved the initial translocation of captive-reared kestrels into four isolated populations and long-term nest-site management and monitoring. We show that after 20 years these four populations have different recovery trajectories including, local extinction, recent decline and comparative stability. We explore the demographic drivers behind these trajectories and how they have been influenced, and could potentially be manipulated, by conservation management actions. Metrics of breeding performance differed between populations and in part this was driven by nest-site selection, with kestrels nesting more frequently, laying larger clutch sizes and rearing larger broods in nestboxes. We found no compelling evidence for inter-population variation in survival rates. Simulating population trajectories under a range of conservation management scenarios, including further conservation translocations or a scaling up of nest-site management, suggested that the latter would be a more effective, practical long-term solution for the population currently in decline. Our findings provide valuable insights into the merits of monitoring, population demographic reviews and the challenges associated with identifying and mitigating for the drivers of rarity in threatened species.
... Reintroduction of Peregrines in Eastern USA restored the species to a large geographical region where breeding had ceased due to pesticide poisoning (Cade & Burnham 2003). Conversely, attempts to re-establish extinct populations of Aplomado Falcons Falco femoralis in Southern USA were less successful, where failures were attributed to climate conditions and habitat changes with associated high predation rates and prey loss (Hunt et al. 2013). On-going efforts to re-establish locally adapted, tree-nesting populations of Peregrines have had varying degrees of success (Kirmse 2001, Sielicki & Sielicki 2009). ...
... A consequence of the imbalanced operational sex ratio was that λ obs of our study population was 13% lower than that predicted solely by the female-based demographic model. We suspect this may not be uncommon in the Accipitriformes, as well as in other orders of raptors with similar selection pressures on age at first breeding (e.g., Hunt et al. 2013). Typically, researchers employ femalebased demographic models in population studies of raptors (Lahaye et al. 1994, Katzner et al. 2006, Ortega et al. 2009, Krüger et al. 2010, Hernández-Matías et al. 2013, Monzón and Friedenberg 2018. ...
Life-history theory predicts individuals should breed as soon as they are able to reproduce, but many long-lived birds delay breeding. In the Accipitriformes, delayed breeding is the norm, and age when breeding begins is influenced by competing selective pressures. In most Accipitriformes, the reproductive roles of males and females differ; males do most of the foraging and females tend eggs and young. Thus, sexual differences in age at first breeding might be expected, but these differences, possible causes, and implications for individual fitness have received little study. We investigated sexual differences in age at first breeding in a marked population of Cooper’s Hawks (Accipiter cooperii) from 2011 through 2018 in central New Mexico, USA. We hypothesized that males required more experience to pair and breed successfully than females, and we predicted: (1) a lower mean age at first breeding for females than males, and (2) that expected individual fitness of early-breeding males would be lower than for early-breeding females. We found that 79% more females than males bred in their first year (hatching year, HY), and expected individual fitness of HY-breeding females was 21% greater than for HY-breeding males. HY males that attempted to breed settled on nesting territories with exceptionally high prey abundance, nevertheless they experienced 37% lower second-year survival than males that delayed breeding. Females competed for mates based on male age. HY females that paired with relatively older males had 33% higher second-year survival and 16% higher expected individual fitness than HY females that initially paired with relatively younger males. The observed annual rate of growth (λ) of our study population was 1.08, closer to λ predicted by male (1.02) than female (1.21) demographic models. Delayed breeding by males thus had important ramifications for λ, highlighting the need to consider sexual differences in age at first breeding in demographic analyses.
A program to reintroduce the Northern Aplomado falcon (Falco femoralis septentrionalis) in south Texas and the southwestern United States was initiated in the late 1970s. Fledgling Aplomado falcons were first released in the Laguna Atascosa National Wildlife Refuge in 1993 and the first nesting pair in the area was recorded by 1995. During 2004–2017 we collected addled eggs from nesting pairs in the Laguna Atascosa National Wildlife Refuge and Matagorda Island in south Texas, to determine if environmental contaminants in Aplomado falcon eggs had decreased over time and if eggshell thickness values were similar to those in the pre-DDT era. We analyzed organochlorine pesticides, PCBs, and PBDEs in 60 egg homogenates by gas chromatography-mass spectrometry. Eggshells were measured to determine thickness and to correlate with contaminant concentrations. Mean concentration in eggs were 244 ng/g ww for p,p’- DDE, 270 ng/g ww for PCBs and 10 ng/g ww for PBDEs. These values were lower than those reported in a previous study for eggs collected between 1999 and 2003, with a mean of 821 ng/g ww for p,p’-DDE and 1228 ng/g ww for total PCBs. Eggshell thickness ranged from 0.206 mm to 0.320 mm (n = 156). Overall, contaminant concentrations in eggs of Aplomado falcons were low, at levels not likely to impact the recovery of the species. Data from this and previous studies indicate that DDE has decreased significantly in eggs of Aplomado falcons over the last 25 years in south Texas. Breeding populations have been steady at over 30 breeding pairs in south Texas since 2011, although they decreased to 24 pairs in 2018 following Hurricane Harvey.
We located two populations of endangered Aplomado Falcons (Falco femoralis) in desert grasslands in north-central Mexico in 1992. During spring 1993, we quantified breeding success, habitat use, and prey selection by the easternmost population, which is located 40 km from the United States. We captured 17 individuals (one subadult male, seven adult males, three subadult females, six adult females) and placed tail-mounted radio transmitters on 15 of them. Females weighed 50% more, had tails 9% longer, and had wing chords 11% longer than males. Breeding season ranges of six radio-tagged individuals monitored more than 100 d ranged from 3.3 - 21.4 km2. Woody plant density ranged from 11.2 - 139.5/ha and percentage of ground-cover ranged from 28.9 - 69.5% in ten falcon territories. Six of seven nests were in yuccas (Yucca elata, Y. torreyi). Seven nesting pairs had a mean clutch size of 2.6, mean hatching success of 1.6, and a mean fledging success of 0.6. We identified 87 prey items from pellets, prey remains, and observed successful hunts; 82 were avian and 5 were insect. Meadowlarks (Sturnella spp.) were most abundant on potential prey transects and in the diet of Aplomado Falcons. Brown-headed Cowbirds (Molothrus ater), Greater Roadrunners (Geococcyx californianus) and hummingbirds (Trochilidae) were identified in diets, but were not detected on transects.
Breeding populations of grassland birds are declining across North America. Alteration of wintering-ground habitat in Mexico may be a significant causal component in these declines, considering the rapid changes in land use occurring there. We investigated the influence of precipitation, habitat structure, and plant community on the abundance and distribution of grassland passerines in the state of Chihuahua, Mexico. We conducted bird and vegetation surveys during 1998–2007 in 65 plots at two study areas 75 km apart, Sueco and Tinaja Verde. Grassland guild species were the dominant component of the wintering bird community at both study areas. Passerine density at Sueco during winter was directly related to cumulative rainfall from the preceding December to September, a factor known to be strongly correlated with grass production. Herbaceous and woody vegetation structure and habitat type influenced occurrence of migratory grassland birds at the plot level. Nine of 11 study species occurred in a greater proportion of plots at Sueco than at Tinaja Verde, even though grasslands at the latter area were apparently in better condition. Whereas we may have overlooked key factors differentiating habitat quantity in the two study areas, some of the evidence suggests that Sueco is on a migratory route and Tinaja Verde is not. The future of desert grasslands in Chihuahua is in peril because of the ongoing wide-scale conversion to agriculture there and climate-change predictions of lower rainfall in coming decades.