2011 Aplomado Falcon Territory Occupancy Survey Summary - South Texas
Paul Juergens— 05 June 2011 — in Aplomado Falcon Restoration Share
Like in years past, we spent approximately one month in southern Texas surveying suitable habitat and, predominantly, historically occupied falcon territories in the areas in and around Matagorda Island National Wildlife Refuge (MINWR) and Laguna Atascosa National Wildlife Refuge (LANWR). The main goal of the survey was to determine territory occupancy.
The survey occurred from 14 April to 12 May and was conducted by myself, Brian Mutch, and Bill Heinrich. The weather and road conditions were much more favorable for our survey efforts this spring as compared to 2010. Generally temperatures were very warm to hot during the days along with the typical high humidity and wind which made the early morning and late evening ideal times for survey. Heat shimmer and high wind in the mid-day hours made survey work at that time difficult and slow. The falcons were often observed mid-day laying low in the shade of their nest structures or nest trees or in nearby mesquites or yuccas and overall inactive. Road conditions were superb in that roads were not inundated and muddy, but unfortunately this comes with a cost and that being a tremendous lack of rainfall since fall 2010.
The area was very dry and dusty, and the developing drought conditions had already begun showing in the vegetation, primarily in the Gulf cordgrass which lacked its usual verdant hue. These dry conditions are rather unfortunate as the area had just last spring received much needed relief from one of the most severe droughts on record. Hopefully this summer the area will receive tropical moisture from the Gulf and provide much needed rain to the area in lieu of entering into another long drought. None-the-less, the falcons looked healthy and were often seen with crops early in the morning indicating their prey was easily procured. This was no surprise as the migration of small birds along coastal Texas this April and May was nothing short of impressive; we frequently observed large numbers of various species of orioles, warblers, thrushes, buntings, flycatchers, blackbirds, and hummingbirds along with yellow-billed and black-billed cuckoos, dickcissels, mourning dove, etc. Eastern meadowlarks, Cassin’s and Botteri’s sparrows, horned larks among other local breeding songbirds also were in abundance. Despite the developing dry conditions along the coast, the prey available to the falcons seemed more than adequate for the meantime.
During the survey period, we observed 79 falcons. This includes falcons occupying 34 territories and an additional 12 individuals observed (4 adult females, 2 juvenile females, 2 unknown females, 1 adult male, 1 juvenile male, 1 unknown male, and 1 unknown falcon). We surveyed 44 territories of which 34 (77%) were occupied. Two new territories in habitat we annually survey in the MINWR area were added to the existing territories surveyed. This year we also surveyed a territory we were not able to access last year in the LANWR area. This brought the total number of territories surveyed up from previous years. I think it is important to reiterate that these “new” territories are within habitat we have surveyed annually for many years now. Here are the results for each survey area.
Total territories surveyed: 44 (MINWR – 18; LANWR – 26)
Most of the pairs observed were at some point during the survey incubating eggs (14 LANWR, 9 MINWR) or brooding young (1 LANWR, 1 MINWR). One of the pairs of falcons observed incubating early in the survey in the LANWR area had failed for unknown reasons. However, we suspect that the nest may have been abandoned by the female as a result of an unsuccessful attempt at polygyny involving a neighboring territorial male falcon. In the MINWR and LANWR areas combined, the 9 other pairs were, at the very least, observed at a nest site/territory and hunting cooperatively, copulating, etc. This year we did not find as many territories with lone females perched at nest sites especially in the LANWR area where a net increase in the pairs observed occurred; however, we did continue to see juvenile males paired with adult females. While we would prefer to see adult male falcons filling in vacancies in territories, the fact that juvenile males were present to recruit into the population is better than none at all. Perhaps in the next year or two, we will begin to see unpaired male aplomado falcons as part of a “floater” population in our survey area. In summary, our results essentially mimic those of recent years and certainly suggest stability in this population along the Texas coast.
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