Northern Aplomado Falcon (Falco femoralis)
- Other Names
- Aplomado Falcon
- Texas Status
- U.S. Status
- Endangered, Listed 2/26/1986
- The beautiful aplomado falcon has a steel grey back, red breast, black "sash" on its belly, and striking black markings on the top of its head, around its eyes, and extending down its face.
- Life History
- Aplomado falcons are most often seen in pairs. They do not build their own nests, but use stick nests built by other birds. Pairs work together to find prey and flush it from cover. Aplomados eat mostly birds and insects. They are fast fliers, and often chase prey animals as they try to escape into dense grass. Parents make 25-30 hunting attempts per day in order to feed their young. Chicks are fed 6 or more times each day. They live up to 20 years in captivity. Falcons are being reintroduced in south Texas to bring back the population.
- Aplomado falcons require open grassland or savannah habitat with scattered trees or shrubs.
- In Texas, aplomado falcons are found in the South Texas and Trans-Pecos regions. Their geographical distribution extends to the southern tip of South America.
- Threats and Reasons for Decline
The Northern Aplomado Falcon was most commonly observed and collected in its U.S. range during the period 1870-1930. The falcon seemingly disappeared in the U.S. after the 1930s for reasons that largely remain a mystery. It is noteworthy to consider that the Aplomado Falcon was at the northern limits of its continental range in southeastern Arizona, southern New Mexico, and western and southern Texas; and, therefore, possibly vulnerable to small changes in habitat quality in this region.
Severe overgrazing by domestic livestock and resultant brush encroachment in the Southwest, including Texas, has been most frequently implicated as the principal cause for the species' decline. Direct adverse effects of livestock grazing on potential falcon prey species have also been suggested as a possible cause. However, a recent review of the history of livestock trends and practices and other ecological factors in the Southwest in relation to the decline of Aplomados suggests different causes.
In the late-1800s, large numbers of cattle were introduced onto Southwest grasslands occupied by Aplomados and their numbers remained high through the 1920s. Decades of overstocking had degraded desert grasslands by the 1920s. Recognition of this led to reductions in cattle numbers by the late-1920s and 1930s, particularly after passage of the Taylor Grazing Act in 1934. However, cattle stocking rates may have remained comparatively high in western and southern Texas well into the late- 1900s, since these ranges were mostly in private ownership and not subject to regulation by the federal act. At least at some Arizona and New Mexico sites where Aplomados occurred, brush did not extensively invade into grasslands until after the 1940s
There is some evidence from early naturalists to support the notion that prairie dogs greatly expanded in the Southwest after the introduction of large cattle herds. Widespread and intensive grazing by cattle may have stimulated such an expansion, since prairie dogs require low-stature grassland habitats. Regardless of the cause, prairie dog numbers and acreages occupied were extremely high during the late-1800s through about 1920. A U.S. government campaign to control prairie dogs on publicly-owned lands in Arizona and New Mexico by use of strychnine poison began in 1912, and a similar state effort was initiated in Texas in 1915. Prairie dogs were substantially reduced through poisoning by the 1920s, their decline peaked in the 1930s, and they were virtually eliminated from southeastern Arizona and southwestern New Mexico by the 1940s and 1950s, respectively. This pattern of decline was probably mirrored in western Texas, except that prairie dogs were never completely eradicated and some populations have persisted there through the present time.
Historic ranges of the blacktailed prairie dog and the Northern Aplomado Falcon in the Southwest, to include western Texas (prairie dogs never occurred during historic time in southern Texas), matched closely. This has led to speculation that habitat conditions generated by prairie dogs may have benefited Aplomado Falcons. It is reasoned that overall abundance, biomass, and catchability of avian and small mammal prey were greater inside prairie dog towns than in the surrounding grasslands. At least some potentially important avian prey species, such as meadowlarks, some plovers, Mourning Dove, Horned Lark, and others, seem to respond positively to grazing. Others, like the Borrowing Owl, are directly dependent on prairie dog borrows and other prairie dog habitat features for optimal nesting and rearing of young. Insects, reptiles, birds, and small mammals that used prairie dog colonies were probably easier to detect and catch by Aplomados than in surrounding grasslands, where herbaceous vegetation was denser and higher. In similar ways, cattle grazing may have provided short-term benefits to Aplomados.
The natural coincidence of Aplomado and prairie dog distributions in the Southwest (outside southern Texas) and their simultaneous declines suggest that these events may have been related. Prairie dogs were eradicated by strychnine poisoning. This method of control was nonselective and undoubtedly killed other wildlife in the vicinity of dog towns. Aplomado Falcons could have been adversely affected by feeding on poisoned birds and mammals through relay toxicity. Relay toxicity also could have killed other raptors and ravens that provided nest platforms for Aplomados.
It appears that a majority of historic encounters with Aplomado Falcons and high numbers and acreage of black-tailed prairie dogs coincided with historically high livestock stocking rates on Southwest grasslands (all between 1870 and 1920). Aplomado falcons and blacktailed prairie dogs, with overlapping distributions, disappeared from the Southwest landscape in the 1930s. Although, it is clear that prairie dogs were intentionally eradicated, causes of the Aplomados disappearance remain obscure. In Arizona and New Mexico, large scale mesquite and other shrub invasion into grasslands appears to have occurred after the demise of the falcon.
Other factors could have affected the decline. Aplomado Falcons disappeared rapidly throughout their U.S. range, which suggest that a widespread phenomenon such as climate change could have been involved. Throughout the U.S. and Mexican range of the Northern Aplomado Falcon, the long-term, cumulative impact of cattle grazing to the recovery of this subspecies probably has been negative, since it eventually contributed to the evident degradation of desert and coastal grasslands. Grazing by cattle increases the spread of mesquite, diminishes water retention on rangelands through soil compaction and loss of herbaceous plant cover, and interrupts natural fire regimes by reducing plant fuel loads. In southern Texas, relatively high numbers of falcon eggs and specimens were collected by professional collectors during the early-1900s and possibly contributed to the disappearance of Aplomados in that region. Particularly in southern Texas and eastern Mexico, but also portions of the Aplomado's former desert range, large tracts of native grassland have been converted to pasturelands and croplands, thereby further reducing the extent and quality of Aplomado Falcon habitat.
The pesticides DDT and DDE were not factors in the Alpomado's disappearance, since they were not introduced into the environment until the late-1940s. Even though these pesticides have been banned in the U.S. for over 30 years, heavy concentrations of DDT and DDE persists in potential prey species in the U.S. and northern Mexico. Furthermore, these pesticides are still in use in Mexico and other parts of Latin America. In eastern Mexico, DDT and DDE contamination has led to severe eggshell thinning in Aplomados. Birds and other organisms collected over the past decade from the lower Rio Grande, Laguna Madre, and other southern Texas locations contained heavy loads of PBCs, heavy metals, and organochlorine pesticides. Organophosphate pesticides are still heavily used throughout the range of the Aplomado Falcon, including in the U.S., and remain a serious threat to Aplomados. This group of pesticides has been linked directly to the deaths of thousands of songbirds, waterfowl, and raptors in Argentina and parts of the U.S. Other threats include direct loss of habitat from various forms of human development, secondary lead poisoning through ingestion of game birds (doves and quail), electrocution by improperly designed electrical transmission lines, and human disturbance in breeding areas.
- Ongoing Recovery
In 1986, the Northern Aplomado Falcon was federally listed as endangered in the U.S. and Mexico based on evidence of population declines in the U.S. and threats to reproduction in eastern Mexico related to pesticide contamination. Subsequently, the northern subspecies was state-listed as endangered in Arizona, New Mexico, and Texas, and in 1990 a federal recovery plan was prepared.
In the years since listing occurred, general awareness of the Aplomado's peril has grown, surveillance of the falcon has increased, consideration of and planning for Aplomado habitat requirements on public lands has improved; and new research, focused on the Aplomado's population ecology and habitat preferences and requirements, has been initiated. In 1992, two small, isolated populations of Aplomados were discovered in north-central Chihuahua, Mexico in close proximity to the U.S. Ongoing monitoring and research efforts at these sites are providing important insights into the desert grassland ecology of this species. Recently, another researchmanagement effort led by U.S. departments of Interior and Defense characterized occupied Aplomado Falcon habitat in northern Mexico and then used that habitat "footprint" to identify potentially suitable falcon habitat in the U.S. The Turner Endangered Species Fund also recently funded a historical review of land use and ecological conditions that surrounded the Aplomado in the Southwest at the time of its decline.
Reintroduction of captive-reared Aplomados into the historic U.S. range was considered an essential step in the 1990 federal recovery plan. As early as 1977, the Chihuahuan Desert Institute at Alpine, Texas had begun a captive breeding program based on wild- captured Aplomado breeding stock from southeastern Mexico. In the 1980s, this program was taken over and expanded by The Peregrine Fund, a private organization focused on the worldwide conservation of birds of prey, with support from the U.S. Fish and Wildlife Service. An initial release of captive-reared young was made on the King Ranch in Kleberg County, Texas in 1985. Additional release sites on the Texas Gulf Coast were evaluated between 1985 and 1987, and the release program was then refocused to Laguna Atascosa National Wildlife Refuge and Matagorda Island. The first breeding in the wild of released captive-reared Aplomados occurred in 1995. Since 1997, over 100 captive-reared young have been released annually along the Texas Gulf Coast. To date, this program has resulted in the establishment of at least 37 Aplomado pairs that have produced over 92 young in the wild. In 2002, reintroductions were expanded to desert grasslands in western Texas with the release of 36 captive-reared young and future releases are being planned for southern New Mexico. The preliminary results of the reintroduction program look promising; ultimately, however, its success will depend on the quality of these environments to support wild Aplomado Falcons over time.
- How You Can Help
Aplomados can be sensitive to human disturbance, especially during the breeding season. Human activity, including close or prolonged intrusion in a bird's territory, or loud and unusual noises, can cause nest abandonment. Human intrusions can also make Aplomados more susceptible to detection and harm from potential predators. A safe viewing distance is 200 yards or more. Suitable viewing at this or greater distance may require a spotting scope with 10 to 15 X or greater magnification. Birders should always respect private property rights in Texas regardless of the species being pursued.
Birders should keep in mind that Aplomados remain extremely rare in Texas and are federally- and statelisted as endangered. Therefore, all reasonable and suspected sightings of this bird should be reported immediately to an expert birder, Texas Parks and Wildlife Department, or the U.S. Fish and Wildlife Service for further verification. Observations should include a detailed description of the bird's location, appearance, activity, and surroundings. Verification of sightings is extremely important in the context of the Aplomado's scarcity and future conservation.
Ultimately, recovery of Aplomados in Texas will depend on the interest and direct involvement of private land owners since lands within the falcon's former range are mostly in private ownership. Texas land holders interested in promoting Aplomado Falcon conservation measures should consult with experts in the Texas Parks and Wildlife Department, U.S. Fish and Wildlife Service, or The Peregrine Fund for technical guidance and other assistance. Texans can contribute to nongame wildlife resources conservation by supporting the Texas Parks and Wildlife Department's "Special Nongame and Endangered Species Conservation Fund" and by purchases of special nongame decals and stamps issued by the department. A set portion of the revenues generated by these programs is used to purchase endangered species habitats and to support the publication of nongamewildlife informational materials and other nongame activities.