Ectoparasites of Burrowing Owls (Athene cunicularia hypugaea) wintering in southern Texas.
Little is known about the winter ecology of the Western Burrowing Owl (Athene cunicularia hypugaea), a declining subspecies in North America (Wellicome & Holroyd 2001; Klute et al. 2003). The Western Burrowing Owl is mostly migratory, breeding in the south-central Canadian prairies and in desert or prairie habitats of the western United States and north-central Mexico. The winter range includes parts of the southwestern United States (including southern Texas) and Mexico. Loss of habitat, especially the conversion of grassland for agricultural production, has contributed to the decline of this subspecies (Klute et al. 2003). The Western Burrowing Owl is endangered in Canada, threatened in Mexico, and is considered to be a Bird of Conservation Concern in the United States by the U. S. Fish and Wildlife Service (Klute et al. 2003).
Burrowing Owls nest in abandoned burrows of prairie dogs (Cynomys sp.), ground squirrels (Spermophilus sp.), land tortoises (Gopherus sp.), foxes (Vulpes and Urocyon sp.), badgers (Taxidea taxus), skunks (Mephitus, Spilogale, and Conepatus sp.), and armadillos (Dasypus novemcinctus) (Fisher 1974), or they may nest in other natural (e.g., rock crevices) (Rich 1984) or artificial burrows (Smith & Belthoff 2001a). Parasites associated with mammals inhabiting the burrows have received attention due to the risk of sylvatic plague (from infection by the bacterium Yersinia pestis) carried by fleas (Tyler & Buscher 1975). In much of southern Texas, however, mammal burrows are scarce due to widespread cultivation. Many wintering Burrowing Owls roost at road culverts or in a variety of other manmade or natural cavities. Of 46 Burrowing Owl roost sites in southern Texas, only 11% were classified as natural burrows (Williford et al. 2006).
Arthropods, especially various species of mites, are common in raptor nests (Philips & Dindal 1977). Heavy infestations of avian ectoparasites can produce severe reactions in their hosts, sometimes even causing death. Ectoparasites have been identified on adult and nestling Burrowing Owls during the breeding season (Hubbard 1968; Thomsen 1971; Tyler & Buscher 1975; Philips & Dindal 1977; Clayton 1990; Baird & Saunders 1992; Smith & Belthoff 2001b), however, nothing is known about the occurrence of ectoparasites on Burrowing Owls wintering in southern Texas. The objectives of this study were to identify and determine the relative abundance of ectoparasites present on Burrowing Owls wintering in southern Texas.
MATERIALS AND METHODS
Fifteen Burrowing Owls were captured with noose traps at their roost sites in Nueces, Jim Wells, and San Patricio counties, in southern Texas, during the winters of 2001-2002 and 2002-2003. Of the 15 owls captured, 13 were roosting at road culverts in agricultural areas. The remaining two owls were roosting in grassland habitats at structures other than culverts (an artificial burrow and an eroded space under a concrete ledge). One owl was captured twice, once during each of the two winters of the study.
Each captured owl was examined for visible ectoparasites by searching approximately 2 [cm.sup.2] of skin and all parts of feathers (within the 2 [cm.sup.2]) in each of the following regions frequently known to harbor parasites: upper leg, crown, under-wing, and vent. Occasionally, an ectoparasite was found crawling on the hands of the examiner while the owl was being searched. Parasites were preserved and stored in 70% ethanol for later identification.
Parasites were examined using compound and dissecting microscopes with bright-field illumination. To aid identification, digital images were also captured with Miotis Images software (2000: Version 1.3), using a National digital camera mounted to a dissecting compound microscope. Photographs were sent to experts on Burrowing Owl ectoparasites for identification.
Ectoparasites were found on four (27%) of the 15 Burrowing Owls. Two of the three genera of chewing feather lice (ITIS 2004) known to parasitize owls (Clayton 1990) were found on Burrowing Owls wintering in southern Texas. A total of eight ectoparasites representing two species of feather lice were found on the Burrowing Owls. Four Colpocephalum pectinatum (Order: Phthiraptera, Suborder: Amblycera, Family: Menoponidae) were collected from three owls, and four Strigiphilus speotyti (Order: Phthiraptera, Suborder: Ischnocera, Family: Philopteridae) were found on three owls. Both species were found on two Burrowing Owls. Of the four owls with lice, the maximum number of lice found per bird was three. The owl that was captured twice (each of the two winters) had the same number (one) and species (S. speotyti) of louse found upon each capture. No fleas, ticks, mites, or wingless dipterans were found on any of the Burrowing Owls captured.
The captured owls were, at most, only lightly infected with lice. It is unknown how these results compare to numbers of lice on museum specimens. However, results from this study are similar to at least two other reports. Smith & Belthoff (2001b) collected eight S. speotyti from 11 adults and four broods of Burrowing Owls in southwestern Idaho. Thomsen (1971) stated that some of the Burrowing Owls examined in California carried "a few" C. pectinatum lice. Based on Smith's (1999) classification, all of the Burrowing Owls captured in southern Texas had an infestation level of "low" (five or fewer individual ectoparasites). In contrast, over 40 lice were found on a single Burrowing Owl in southwestern Idaho (Smith 1999). This infestation may have caused reproductive failure of this particular owl.
Population-level effects of ectoparasites on Burrowing Owls have not been established. Nesting Burrowing Owls may be more susceptible to ectoparasites than wintering Burrowing Owls. Underground burrows create a favorable environment for ectoparasites, because burrows maintain moderate temperatures and high humidity (Kennerly 1964). Eveleigh & Threlfall (1976) suggested that birds nesting in colonies are more susceptible to infestation due to frequent contact between individual birds. Although not considered a colonial nesting species, Burrowing Owl use of prairie dog burrows creates a loose "colony" by bringing nesting pairs and broods of Burrowing Owls into close proximity to one another. Dependence upon mammal burrows for nests also makes Burrowing Owls vulnerable to fleas (James & Harwood 1969), since fleas can transfer to owls from burrowing rodents (Philips & Dindal 1977). Burrowing Owl nests may harbor at least 39 different arthropod species, a minimum of 15 of which are fleas (Philips & Dindal 1977). Indeed, of six published studies on Burrowing Owl ectoparasites, at least four found lice, and all but one (Tyler & Buscher 1975) found fleas (Hubbard 1968; Thomsen 1971; Philips & Dindal 1977; Baird & Saunders 1992; Smith & Belthoff 2001b). In Idaho, 143 fleas were collected from 11 adult Burrowing Owls and four broods, whereas only eight lice were collected from the same owls (Smith & Belthoff 2001b). Although fleas were much more common on breeding owls in Idaho, only a sample of ectoparasites were collected from each owl captured, so the total number of fleas and lice on owls in Idaho actually was higher than indicated (B. W. Smith, pers. comm.).
Perhaps the most significant finding in this study is that no fleas were found on any of the 15 owls examined from southern Texas. Although temperatures below 18[degrees]C are considered less favorable for egg-laying among many flea species (James & Harwood 1969), the weather in southern Texas often exceeds 18[degrees]C during winter. The lower temperature limit for development (egg to adult) of the cat flea (Ctenocephalides felis) is 13[degrees]C, with an upper relative humidity limit of 92% (Silverman et al. 1981). Adult Pulex irritans, a flea often found on breeding Burrowing Owls (Thomsen 1971; Philips & Dindal 1977; Baird & Saunders 1992; Smith & Belthoff 2001b) and other burrowing animals (Baird & Saunders 1992) can survive for 125 days with no food at 7-10[degrees]C (James & Harwood 1969). In Corpus Christi, the mean winter temperature (December-January) during this study was 14.2[degrees]C with relative humidity ranging from 67%-87% (National Weather Service 2002-2003). Both temperature and relative humidity measures during this study were within the limits for the development of at least these two species of fleas.
The absence of fleas on captured burrowing owls may be attributable to the fact that 13 of the 15 owls captured (87%) were roosting at road culverts. Since mammals in the area are not known to regularly use road culverts as burrow sites, the culverts probably did not harbor large flea populations. Moreover, unlike nesting Burrowing Owls, wintering Burrowing Owls do not roost inside their burrows. Most Burrowing Owls in southern Texas roost at the entrance to the burrow and enter the burrow's interior only briefly for protection from inclement weather or to avoid avian predators.
Wide dispersal on the winter range may also greatly limit the incidence of ectoparasite transfer between Burrowing Owls, as winter roost sites in southern Texas are scattered throughout open areas. It is not uncommon to drive > 1 km to observe two Burrowing Owls.
Although sample size is small, the low numbers of lice and the total lack of fleas in this study of Burrowing Owls wintering in southern Texas indicate that the winter habits (i.e., use of widely dispersed road culverts instead of natural mammal burrows) may be advantageous in avoiding ectoparasites, especially fleas.
We would like to thank Brian W. Smith at the Kentucky Department of Fish and Wildlife Resources for information regarding ectoparasites of Burrowing Owls in Idaho. We would also like to thank James R. Belthoff, Professor and Director of Graduate Studies for the Department of Biology at Boise State University, for providing resources and direction. We are especially grateful to Dale H. Clayton, Professor for the Department of Biology at the University of Utah, for identifying the ectoparasites. Gregory Stunz, Assistant Professor for the Department of Science and Technology at Texas A & M University-Corpus Christi, provided the use of his lab and microscope/camera set up. Roy Parker, Texas Cooperative Extension office, Texas A & M University, provided information regarding fleas. We also thank Tom Skoruppa, Jon T. Skoruppa, Chanda Littles and Jennifer Ortega for their assistance in the field. Helpful reviews of the manuscript were provided by Laverne Cleveland, Brian Smith, Bart Cook, and two anonymous reviewers.
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MKS at: firstname.lastname@example.org
Mary K. Skoruppa, Bryan Pearce*, Marc C. Woodin and Graham C. Hickman*
U. S. Geological Survey, Texas Gulf Coast Field Research Station
Corpus Christi, Texas 78412 and
*Texas A & M University-Corpus Christi, Department of Physical & Life Sciences
Corpus Christi, Texas 78412
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|Author:||Skoruppa, Mary K.; Pearce, Bryan; Woodin, Marc C.; Hickman, Graham C.|
|Publication:||The Texas Journal of Science|
|Date:||Feb 1, 2006|
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