Brian Mutch’s research while affiliated with The Peregrine Fund and other places

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.

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.

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.

Habitat availability might be the most important determinant of success for a species reintroduction program, making investigation of the quality and quantity of habitat needed to produce self-sustaining populations a research priority for reintroduction ecologists. We used a stochastic model of population dynamics to predict whether attempts to improve existing breeding territories using artificial nest platforms improved the population growth rate and persistence of a reintroduced population of Northern Aplomado Falcons Falco femoralis septentrionalis in South Texas. We further assessed whether the creation of new territories, i.e. conversion of entire areas to suitable habitat and not simply the erection of nest platforms, would lead to a subsequent increase in the nesting population. Our model was able to reproduce several characteristics of the wild population and predicted the number of breeding pairs per year strikingly well (R2 = 0.97). Simulations revealed that the addition of nest platforms improved productivity such that the population would decline to extinction without them, but is stable since their installation. Moreover, the model predicted that the increase in productivity due to nest platforms would cause the population to saturate available breeding territories, at which point the population would contain a moderate proportion of non-territorial birds that could occupy territories if new ones become available. Population size would therefore be proportional to the increase in available territories. Our study demonstrates that artificial nest sites can be an effective tool for the management of reintroduced species. This article is protected by copyright. All rights reserved.

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.

Bullet fragments in rifle-killed deer (Odocoileus spp.) carrion have been implicated as agents of lead intoxication and death in bald eagles (Haliaeetus leucocephalus), golden eagles (Aquila chrysaetos), California condors (Gymnogyps californianus), and other avian scavengers. Deer offal piles are present and available to scavengers in autumn, and the degree of exposure depends upon incidence, abundance, and distribution of fragments per offal pile and carcass lost to wounding. In radiographs of selected portions of the remains of 38 deer supplied by cooperating, licensed hunters in 2002–2004, we found metal fragments broadly distributed along wound channels. Ninety-four percent of samples of deer killed with lead-based bullets contained fragments, and 90% of 20 offal piles showed fragments: 5 with 0–9 fragments, 5 with 10–100, 5 with 100–199, and 5 showing >200 fragments. In contrast, we counted a total of only 6 fragments in 4 whole deer killed with copper expanding bullets. These findings suggest a high potential for scavenger exposure to lead.

The northern aplomado falcon (Falco femoralis septentrionalis) was once fairly common in the savannas of southern Texas and in other parts of the American Southwest but virtually disappeared by the 1950s north of the Mexican border. It was federally listed as endangered in 1986. The Peregrine Fund established a captive breeding program based on 25 nestlings obtained from eastern Mexico during 1977–1988. Following a pilot release project in 1985–1989, a full-scale release effort in the southern Texas plain began in 1993 employing techniques similar to those we developed for the peregrine falcon (Falco peregrinus). We produced 923 fledgling aplomado falcons, of which 812 were released in Texas on both federal wildlife refuges and private property. We observed released falcons breeding in the wild for the first time in 1995, and by 2002, 37 pairs were known and at least 87 wild young had fledged over an 8-year period. Predation by raccoons (Procyon lotor) was a frequent cause of nest failure, and the great horned owl (Bubo virginianus) was the principal source of death in fledglings at hack sites, a factor that may limit aplomado falcon recovery in some areas of its former range. Enrollment of more than 5,500 km2 of private land under federally mediated “Safe Harbor” agreements encouraged landowner goodwill and cooperation and provided essential access to private property by affording relief from potential liability associated with the Endangered Species Act.

Bullet fragments in rifle-killed deer (Odocoileus spp.) carrion have been implicated as agents of lead intoxication and death in bald eagles (Haliaeetus leucocephalus), golden eagles (Aquila chrysaetos), California condors (Gymnogyps californianus), and other avian scavengers. Deer offal piles are present and available to scavengers in autumn, and the degree of exposure depends upon incidence, abundance, and distribution of fragments per offal pile and carcass lost to wounding. In radiographs of selected portions of the remains of 38 deer supplied by cooperating, licensed hunters in 2002–2004, we found metal fragments broadly distributed along wound channels. Ninety-four percent of samples of deer killed with lead-based bullets contained fragments, and 90% of 20 offal piles showed fragments: 5 with 0–9 fragments, 5 with 10–100, 5 with 100–199, and 5 showing >200 fragments. In contrast, we counted a total of only 6 fragments in 4 whole deer killed with copper expanding bullets. These findings suggest a high potential for scavenger exposure to lead.