Spring 2008 Aplomado Falcon Project Update
Paul Juergens— 9 May 2008 — in Aplomado Falcon Restoration    ShareWe are now well into spring and fast approaching summer which means falcons re-established in the wilds of South and West Texas, as well as those in the captive breeding facility in Boise, are well into the nesting season.

On 28 April, we finished up the 2008 South Texas Aplomado Falcon Territory Occupancy Survey. A total of 73 falcons were observed during the survey periods of 13 March to 3 April and 15 April to 28 April. This includes 31 territorial pairs and 11 individuals. Out of the 73 falcons, we were able to determine if 35 (48%) of them were banded or not. We found 11 were un-banded and 24 were banded of which 16 were identified. We surveyed 38 territories in southern Texas of which 31 (82%) were occupied. This includes another new territory near Matagorda Island National Wildlife Refuge. Here are the results for each survey area:

Total territories surveyed: 38
Matagorda Island National Wildlife Refuge (MINWR) – 15
Laguna Atascosa National Wildlife Refuge (LANWR) – 23

Total occupancy: 31/38 (82%)
MINWR – 14/15 (93%)
LANWR – 17/23 (74%)

Notes on LANWR and MINWR:

The occupancy rate for the LANWR area dropped from last year’s 89% to 74%. We felt the prey in the LANWR area wasn’t very abundant, at least compared to what we’ve seen before. The area until recently had not received any rainfall since November of 2007—the lowest rainfall recorded in 90 years. Similar to what senior field biologist Angel Montoya found during his studies in Chihuahua, Mexico, perhaps a lack of prey, even in southern Texas where prey is much more abundant than in the southwestern deserts, has created a situation of unoccupied territories.

Another observation senior field biologist Brian Mutch pointed out is the lateness or even complete lack of falcons laying their eggs at the completion of the survey. Is this another possible result of a momentary lack of prey? While the results of the survey are not substantially alarming and considering populations fluctuate naturally, we still plan to keep a close watch on falcons in the LANWR area.

On a good note since we left South Texas to prepare for the upcoming falcon release season in West Texas and New Mexico, the Lower Rio Grande region has started receiving much needed rainfall…it’s just what the falcons ordered!

Meanwhile on MINWR, everything seems normal with regards to falcons occupying territories and prey populations being substantial. One pair of falcons on Matagorda Island had the misfortune of having their nest box overtaken by Crested Caracaras; however, it didn’t affect occupancy. That particular nest box was of an older design with much wider spacing than what is found on our latest nesting structures. While the caracaras have to contort their bodies to gain access, they have apparently realized the benefit of the nest boxes as well. The new design is several inches shorter and the bar spacing is just wide enough for an Aplomado Falcon to pass through easily but will exclude larger raptors.

After seeing the falcons range around their territory trying to locate other nest sites which are very limited there, we provided the pair with a new nest structure before they resorted to nesting on the ground. Later, we observed them on and in the nest box just two hours after placement! Also during our MINWR area survey, we discovered a new pair of falcons had shown up on a nearby island. This is the third territory to form off of MINWR since 2005, so expansion of this population continues. This is a very good indication of a healthy population even if the expansion is at a slow rate.

Although we have not searched intensively for falcons in western Texas this season, we have made some quick searches and currently know of four pairs near release sites. One pair has nested so close to our hack site that we will need to relocate and build new release towers for the upcoming cohorts of young falcons to be released on the ranch. Nesting Aplomado Falcons tend to defend their territories very aggressively and would see the young released falcons as a threat and treat them accordingly. In other words, the nesting falcons would most likely, on the day of release, attack and possibly make life difficult for the young falcons. We have found this situation is best avoided by relocating the hack site. Ideally release sites are used for many years; however, if a pair of falcons chooses to set up a territory and nest nearby, we will happily build a new release site outside of the established territory.

We placed ten nest structures throughout the coastal plain of Texas this spring. Four nest structures were placed on refuge lands located on South Padre Island, one on the Francine Cohm Preserve located on Mustang Island, and another just across the bay from Matagorda Island NWR. While nesting Aplomado Falcons have not been observed in these areas in the past, we do know that falcons have visited based on valuable observations from birders and biologists working there. We anticipate the continued expansion of falcons from our two core populations and expect falcons will recognize the nest sites. One of the remaining four structures was placed on Matagorda Island as a replacement, two others replaced old nest structures in the Laguna Atascosa area, and the last structure was provided in an existing Aplomado Falcon territory as a new potential LANWR nest site. Although many naturally occurring nests exist within falcon territories, we have found nest success and productivity are much higher from nest structures in southern Texas than natural nests as a whole. In the scheme of species restoration, like captive breeding and release programs, maximizing productivity in the wild is one of the best ways to reach recovery.

Captive Breeding in Boise, Idaho:

The captive breeding of Aplomado Falcons at our facility in Boise, Idaho is well underway, and we eagerly wait for the falcon release season to start. This year we are fortunate to have several hack site attendants returning to watch over a handful of falcons to be brought down from Boise for releases in the beautiful desert grasslands of far western Texas and southern New Mexico. Attendants returning for their second season with the Aplomado Falcon Project include Stefan Calabria, Alyssa Ervin, and Lauren Helton. Another attendant, Kevin Cassel, is returning for a third season. We greatly appreciate their hard work and dedication toward the recovery of this beautiful species.

Thanks for reading and stay tuned for future updates!

Find more articles about Aplomado Falcon, North America