The Northern Aplomado Falcon was once a part of the dynamic and diverse wildlife community associated with our southwestern grasslands, but the species disappeared during the early 20th century. Restoring this species underscores the need to conserve important habitats. This effort is an ideal vehicle to promote creative solutions to problems associated with the Endangered Species Act, such as the innovative “Safe Harbor” permit, which has enrolled more than 2 million acres of potential Aplomado Falcon habitat in the interest of conservation.
Field studies are being conducted to document the status of Aplomado Falcons and to understand their ecology. This effort provides a unique opportunity to study a new population as it begins to occupy both traditional and novel habitats. The Aplomado Falcon is an important “indicator species” for environmental quality due to its unique ecology and propensity to accumulate environmental contaminants. Addled eggs and tissue samples are being analyzed to gain knowledge of contaminant levels throughout the Aplomado Falcon’s range.
At the northern extent of the species’ range in Texas, the Aplomado Falcon is regaining its place as an integral part of the grassland ecosystem from which it has been absent for more than 50 years.
To date, we have installed 137 of our innovative artificial nest structures with approximately 75 in service throughout the range of the recovering South Texas population. Among the 31 known breeding pairs, 26 are using our artificial structures.
We are working with the U.S. Fish and Wildlife Service to identify areas of habitat management need, particularly where brush has invaded grassland habitat not long ago occupied by breeding Aplomado Falcons. The initial phases of habitat management by Laguna Atascosa National Wildlife Refuge staff and cooperators have proven effective, and plans to continue and expand the management of falcon habitat are forthcoming. We have made contact with a large South Texas private landowner to pursue the possibility of also managing habitat on privately held properties.
We are also working to understand the degree to which Aplomado Falcons are exposed to contaminants. At the top of the food chain, the Aplomado Falcon serves as an “indicator species” of environmental quality in its tendency to accumulate contaminants in tissues and eggs.
Aplomado Falcon Releases
The captive propagation and release phase of the Aplomado Falcon recovery effort ended in 2013. During the course of this important aspect of the project, The Peregrine Fund raised 2,102 Aplomado Falcons and sent 1,950 to release sites in New Mexico and West Texas and along the Texas Gulf Coast. It is from these release efforts we have established what appears to be a self-sustaining population of falcons along the Texas Gulf Coast. The Chihuahuan Desert is no longer suitable for the falcon, revealing the importance of our efforts along the Gulf Coast to the survival of the Aplomado Falcon in the United States.
As a follow-up an earlier study, two female falcons released in Texas on South Padre Island (SPI) were fitted with satellite PTT transmitters to further understand falcon survival and dispersal in southern Texas. These two falcons provided interesting data, one traveling more than 100 miles south into Mexico and the other making several trips to the mainland and traveling up the coast north coast. Both falcons were considered to be fatalities in 2013. We continue to monitor one remaining falcon fitted with a PTT that was released in 2012 at Mustang Island. She has almost exclusively remained on the Texas coastal barrier islands, traveling as far as 100 miles north. She successfully nested and fledged young on San Jose Island.
Aplomado Falcon Monitoring
Our survey efforts in South Texas are focused on determining occupancy at all known territories. We observed a total of 68 falcons, which included 30 territorial pairs and 8 individuals. Overall, the number of occupied territories (+2) and individuals observed (+4) increased from the previous year. We continued to see juvenile males paired with adult females. While this illustrates recruitment of males into the breeding population, it also demonstrates a lack of non-breeding adult males. Despite drought conditions, prey in the form of small birds and insects (e.g., cicadas) seems to remain in ample supply.
We are finding that loss of habitat to brush encroachment and potential development is a major concern in the LANWR study area. The two most common woody plant species responsible are mesquite and huisache and could be closely related to the territory occupancy problems in this part of Texas. The refuge began in 2012 to clear mesquite and huisache and re-open the grassland habitat in the Bahia Grande Unit. Where brush has been removed, the desired result of an open grassland habitat has been achieved. Falcons are using the area once again, but much more work needs to be done throughout the study area.
We banded 32 nestlings (16 LANWR, 16 MINWR) and collected blood samples from each of them for genetic analysis. Sixteen addled eggs or eggshell fragments were collected for contaminant studies. Overall, the observed productivity rate was lower than previous seasons, decreasing to 1.5 young per territorial pair for the population as a whole, a condition influenced chiefly by poor productivity in the MINWR population. Furthermore, we encountered an unusually large number of addled eggs. Significant activity on Matagorda Island due to an oil spill clean-up effort occurred when the falcons would have been laying eggs or incubating completed clutches. The amount of disturbance was unprecedented and persisted throughout the incubation period.
Of greatest concern was the drop in productivity on MINWR, together with the increased number of addled eggs collected. As a possible explanation, we learned that a number of oiled birds of various species were found on the beach during the clean-up effort by USFWS personnel, and it is likely that falcons were also exposed to petroleum-based hydrocarbons via oiled prey birds just prior to and during egg laying and incubation. Because of the large number of personnel on the island and the very limited access we were granted, we were not able to observe the nesting falcons for very long and therefore could not determine if any of them had oil on their feathers nor could we detect other evidence indicating direct exposure to oil. We cannot tell for certain whether this potential exposure influenced the high egg mortality/low productivity, or whether the latter resulted from disturbance during incubation. We suspect a combination of both factors. Meanwhile, the productivity rate for LANWR (1.73 young/pair) remained similar to that observed in the previous two years.
We also conducted Aplomado Falcon surveys in the Chihuahuan Desert area of west Texas and New Mexico. Our surveys provide strong evidence that recovery of the Aplomado Falcon in the Chihuahuan Desert is unlikely.
We placed 10 new nest structures; two on San Jose Island, two on Mustang Island, and one on Matagorda Island. The remaining five were placed in the LANWR area. We also serviced 43 nest structures to ensure they were suitable for use during the nesting season. We removed all of the Spanish moss lining from each of the nests and replaced it with 3/8” pea gravel and cedar shavings to avoid nestling entanglement.
Monitoring Remnant Populations in Mexico
Since 1996, we have monitored nest productivity of a small population of Aplomado Falcons in Chihuahua, Mexico. This population has decreased because of drought and the conversion of grasslands to agriculture. Native grasslands, particularly at the Sueco area, continue to be converted to farmland. We are working with state and federal agencies and conservation organizations in Mexico and the United States to address this issue. If the current trends continue, the Aplomado Falcon population in Chihuahua will become extinct during this decade.
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|Video: Artificial insemination technique|