owl

The Cactus Ferruginous Pygmy Owl – is it a real species?

The Cactus Ferruginous Pygmy Owl (Glaucidium brasilianum cactorum) is an alleged subspecies of the Ferruginous Pygmy Owl (Glaucidium brasilianum). Usually when I write of birds, I seek information at the Cornell Lab of Ornithology. But in this case, search for “Cactus Ferruginous Pygmy Owl” or “Ferruginous Pygmy Owl” or “ferruginous owl” yielded no results. When I searched for “pygmy owl” I get an article on the “Northern Saw-whet Owl.” The Sibley Guide to Birds does have a brief article on the “Ferruginous Pygmy Owl” but nothing on the “cactus” variety. In a sense, the Cactus Ferruginous Pygmy Owl is not a species distinct from the Ferruginous Pygmy owl. The same situation holds true for the alleged “southwestern” or “southwest” Willow Flycatcher.

Pygmy owl USFS

The U.S. Forest Service published a long article entitled “Ecology and Conservation

of the Cactus Ferruginous Pygmy-Owl in Arizona.” (Link to report)

They described the owl: “The cactus ferruginous pygmy-owl is a small gray-brown or rufous-brown owl, approximately 16.5 to 18 cm [about 7 inches] long. Wingspan is about 12 inches. In comparison with G. b. brasilianum and G. b. ridgwayi, this subspecies exhibits shorter wings, a longer tail, and generally lighter coloration.” Female typically weigh 75g while males average 64g.

“The vocal repertoire of the cactus ferruginous pygmy-owl comprises several calls, some of which appear to be specific to age or sex of the owl. The advertising call of the adult male is heard primarily at dawn and dusk but also during daylight and even moon rise, especially during the courtship period. It is ventriloquial and consists of a prolonged and monotonous series of clear, mellow, whistling notes… During the breeding season, females utter a rapid chitter, possibly a contact call with the male and juveniles and also for food begging.”

Habitat for the ferruginous pygmy owl is variable. ” Partly because of this species’ plasticity

and partly due to the lack of detailed habitat studies, the habitat requirements of cactorum remain poorly understood.”

“In the eastern part of the range, plant communities supporting the cactus ferruginous pygmy-owl are coastal-plain oak associations, mesquite bosques, and Tamaulipan thornscrub in south Texas …, lowland thickets, thornscrub associations, riparian woodlands and second-growth forests in northeastern Mexico.”

“In western Mexico, the owl may occur in Sonoran desertscrub, Sinaloan thornscrub, Sinaloan deciduous forest, riverbottom woodlands, cactus forests, and thornforests…. In Arizona, the owl is historically associated with cottonwood (Populus fremontii) and mesquite (Prosopis velutina) riparian woodlands …and Sonoran desertscrub.”

Pygmy owls are fierce hunters and frequently attack birds larger than themselves including mourning doves and chickens. They also hunt spiny lizards and rats.

The cactus ferruginous pygmy-owl was first described in the Tucson area in 1872 and naturalists described ” the subspecies as common or fairly common along some streams and rivers of central and southern Arizona.” Some authorities claims there was a sharp decline sometime before 1950, cause unknown, but it is speculated that the decline was due to changes in riparian areas. Some naturalists, however, noted expansion along irrigation canals. The story is also complicated by the fact that early naturalists lumped the Cactus Ferruginous Pygmy owl in with the Northern pygmy owl.

However, according to an exhaustive review of the literature by Attorneys opposing a 2008 petition by the Center for Biological Diversity, the owl was, and is, only a sporadic and localized visitor in Arizona and its population has actually increased slightly over the past 136 years. The claim of a sharp decline in population is unsupported by any documentation. Furthermore, because there is no difference between owls in Arizona and those in Mexico, the establishment of a “distinct population segment” in Arizona is unwarranted.

The range maps below put some perspective on the significance of the Arizona population relative to the population as a whole. However, environmentalists are still trying to get the Arizona population of pygmy owls listed as an endangered species.

Cactus ferruginous owl range map

Ferrugious owl range map

See also:

Pygmy owls and property rights

Whatever happened to Pima County’s Sonoran Desert Conservation Plan?

The Flaws in the Endangered Species Act

 

 

Barn Owls, Tyto Alba?

Tyto alba is a denizen of the night who stalks his prey by sound and stealth. He may have passed you close by but you didn’t notice, or maybe you felt a brief ghostly presence. On silent wings, the Barn Owl (Tyto alba) can hunt in almost complete darkness, relying only on the faint sounds made by his intended meal. Fringe-like feathers on the leading edge of the wings help make the flight silent.

The barn owl is a very adaptable bird of prey that is found in specific habitats on all continents except Antarctica. It is the most widely distributed land bird. Barn owls eat rodents, and perhaps because we humans attract such beasties, barn owls favor nesting near human habitation in barns, under bridges, in mine shafts, and in palm trees. In the southwest, barn owls also nest in undercuts in arroyos, and may be found in desert grasslands, and in trees around agricultural fields.

Barn owls often swallow their prey whole, but they can’t digest fur and bone, so they regurgitate pellets. (Dissection of pellets allows researchers to study what the owls eat.)

Barnowl-female

 

 

 

 

 

 

 

 

 

 

Barn-owl-male

Barn owls are sexually dimorphic, that is, the males and females have differing plumage as you can see in the photos. The females tend to be bigger, darker, and more speckled than the males. The birds average about 12 inches in body length and have wingspans of about 33 inches. Weights in adults vary from 10 to 20 ounces.

The feathers form a facial disk designed to focus sound to the owl’s ears. The ears themselves are not symmetrical on the skull as in other animals. Rather the left ear points downward, and the right ear points upward. Therefore, sound reaches each ear at slightly different times and allows the owl to exactly pinpoint the source. Some researchers claim that each ear hears with slightly different frequency sensitivity. That also aides in sound location. Barn owls are smart and learn all the squeaks and twitters of their prey so that they can identify not only where it is, but also what it is. Perhaps the only rodent with equally good hearing is the Kangaroo Rat.

Birds have four toes or talons. They are configured either three in front – one in back, or two and two. The barn owl can move its outer toes to form both configurations. That enables the owl to form a good web-like trap when snatching prey. The barn owl has serrations on the claw of the middle toe to aid grooming.

Barn owls have many vocalizations, some researchers count as many as 15 distinct calls as well as tongue clicking and wing clapping. Some of the sounds are for proclamation of territory, others are for alarm, and some are for courtship and mating rituals. Many of the sounds are screaming or screeching; others include hissing or wheezing, and whistling. None of the sounds are what we would call an owl hoot.

Nesting occurs in the spring in most areas, but can occur any time of year if there is abundant prey available. The female may lay up to six eggs each one to two days apart. Incubation takes 33 days and the young hatch one to two days apart. If the parents don’t provide enough food, the older chicks starve out and may even consume the younger chicks. The chicks will fledge seven to eight weeks after hatching. Barn owls typically breed at an age of one year, and there is a high mortality rate in the wild. Typical wild life expectancy is 2 years, but captive birds have lived into their high teens.

Barn owls are difficult to observe in the wild because of their nocturnal habits. I have seen them sleeping in mine shafts. If you want to seem them close up, go out to the Arizona-Sonora Desert Museum where Docents frequently have them on display.

Barn-owl-chicks