The band-tailed pigeon (Patagioenas fasciata monolis) is California’s only native pigeon. They inhabit the oak woodland and coniferous forests of the coast and Sierra Nevada mountain ranges in northern California south through the Tehachapi Mountains and Transverse Range into the Peninsular Range in San Diego County. Population indices such as the Breeding Bird Survey, Christmas Bird Count, and the Mineral Spring Survey indicate that band-tailed pigeon populations are on the decline. Reasons for this decline are complex and include:
- unregulated hunting prior to the passage of the Migratory Bird Treaty Act in 1918,
- habitat loss,
- highly variable food resources,
- low reproductive rate,
- poaching, and
Band-tailed pigeons are highly dependent upon oaks and oak woodland habitat for roosting, nesting, and for food. Oak woodland in California has declined significantly over the last 60 years with thousands of acres lost annually to human development. Compounding this are the additive effects of sudden oak death (due to Phytophthora ramorum) killing individual oak trees throughout California. Particularly susceptible are the Quercus species such as coast live oaks (Q. agrifolia), which band-tailed pigeons are highly dependent upon. Mineral springs also are import to band-tailed pigeons in California; pigeons use these sites for drinking water and to ingest sodium, particularly in the spring and summer. However, disturbance of these sites by humans or development may limit use by pigeons in many areas.
Band-tailed pigeons have a plant-based diet, feeding primarily on acorns in the winter and fruit and grain in the summer. These food items can significantly fluctuate from year to year as a result of precipitation and other environmental conditions. These unpredictable food resources influence pigeon movements and reproduction.
Another factor that may contribute to population decline is low reproductive rates. A pair of breeding band-tailed pigeons lays only one egg. Band-tailed pigeons typically breed once a year, but they do have the potential to breed up to two to three times per season when conditions are ideal, for example during times of high food availability, low predation and mild weather.
Poaching and Trauma
Poaching, or illegal take, of band-tailed pigeons is a problem throughout their entire range. Encroachment by humans into pigeon habitat, reduced natural food resources, and loss of habitat also may bring pigeons into closer contact with humans, putting them at an increased risk for poaching or other injury. For example, attacks by domestic dogs and cats and collisions with windows and vehicles are all documented sources of mortality for band-tailed pigeons.
Another often overlooked and potentially additive pressure on band-tailed pigeon populations is Trichomonosis, a disease typically caused by the parasite protozoan Trichomonas gallinae. A variety of bird species are susceptible to infection with Trichomonas parasites. Traditionally, pigeons and doves, along with the raptors that feed upon them, are most commonly infected by this parasite; however, more recently, infection has been reported in a variety of songbirds using bird feeders both in the United Kingdom and in Canada. A few species of songbirds here in California have also become infected with Trichomonas.
Band-tailed pigeons are highly susceptible to infection with Trichomonas parasites. The parasite causes caseous (“cheese-like”) lesions in the mouth and upper digestive tract, severe organ necrosis, and death. When lesions in the mouth or esophagus become severe, the pigeon is unable to swallow food, which eventually leads to emaciation and starvation. The lesions also may block the trachea and interfere with breathing resulting in suffocation and death. Band-tailed pigeons can become infected with Trichomonas parasites through contaminated food or water. Lesions within the esophagus or mouth cause the infected bird to regurgitate food that subsequently becomes contaminated with the protozoan facilitating the spread of infection to other birds. In some areas band-tailed pigeons use bird feeders and bird baths, which are ideal locations for the transmission of the parasites among different bird species. Once band-tailed pigeons become infected, the disease also can be spread to other pigeons though billing or feeding between mates during courtship and the feeding of crop milk to squabs.
Individual adult and juvenile pigeons die year-round from Trichomonosis resulting in a relatively persistent loss of individuals from the population, while large-scale mortality events due to Trichomonosis result in the death of hundreds to thousands of pigeons in a relatively short period of time. Mortality events have been documented in band-tailed pigeons in California since the mid-1940s. These events are characterized by large numbers of dead and dying pigeons in the same geographic location over a short period of time. These events typically occur between December and April and last for a few days to a couple of months. Mortality events involving band-tailed pigeons due to Trichomonosis seem to be occurring with more frequency in recent years; events have been documented almost annually since 2000.
In order to more fully understand the impact of this disease on band-tailed pigeons in California, a cooperative project between the Wildlife Investigations Lab and the UC Davis Wildlife Health Center was undertaken in 2011. The objective of our project is to assess the prevalence of Trichomonas infection in band-tailed pigeons to understand the relationship between infection, pathogenesis and population health. We also will evaluate the genetic diversity of the parasites to better understand strain variation and disease transmission.
In order to meet these objectives, samples have been collected from live-trapped pigeons during the spring and summer from locations throughout California. The live-trapped pigeons are banded with a USFWS leg band.
Samples from hunter-killed pigeons have been collected from Shasta County in the northern hunt zone and from Monterey County in the southern hunt zone. Examination and testing of dead pigeons occurs year round.
Particular attention is directed towards sample collection during mortality events. In 2012, increased mortality involving band-tailed pigeons was reported in two primary locations beginning in early-January. One site was near Carmel Valley in Monterey County; the other site was near Coarsegold in Madera County. Subsequent mortality was reported in six additional counties. Site visits were conducted during the height of these events. Numerous sick pigeons were found among the recently dead, scavenged pigeons, and feather piles at each location. Total mortality from these events is estimated around 5,500 pigeons.
Oral swabs are collected from live-trapped and freshly dead pigeons for culture of the parasite, if present. Samples of the lesions are collected from dead pigeons to recover the parasites. These samples are processed by Dr. Yvette Girard at UC Davis. Once the parasite is isolated, DNA will be extracted to determine the actual identity of the infecting parasite.
Band-tailed pigeons in California face many threats, the greatest being habitat loss, variable food availability, poaching and disease. Populations need to be monitored throughout their range, and any threats to their survival need to be minimized when at all possible. Determining the prevalence and impact of this disease in California’s band-tailed pigeons will allow wildlife agencies to better manage this species, ultimately benefiting the band-tailed pigeons throughout California and beyond.
If you have any questions about the project, or would like to report band-tailed pigeon mortality, contact Krysta Rogers at 916-358-1662.