Got Acorns?

If you have acorns in your area, be on the look out for band-tailed pigeons this winter. Band-tailed pigeons are California’s only native pigeon and this time of year, they will fly great distances to find acorns. Band-tailed pigeons are one of the rare bird species that will actually swallow acorns whole! Unfortunately, this behavior also makes them more susceptible to Trichomonosis, a disease caused by a single-celled microscopic protozoan parasite, Trichomonas gallinae.

Band-tailed pigeon. Photo by Krysta Rogers.

Adult band-tailed pigeon showing the characteristic white crescent and iridescent greenish-bronze patch of feathers on the hind neck and black band on the tail, for which the species was named. Photo by Krysta Rogers, 2013.

The parasite lives in the mouth and throat of infected birds, causing caseous (“cheese-like”) lesions to develop in the bird’s mouth or esophagus. As the lesions become larger, the pigeons can no longer swallow acorns, leading to weight loss and eventually death. The lesions also may cause the pigeon to suffocate, if they block the airway.

Band-tailed pigeons with Trichomonosis. Photos by Jeff Cann & Krysta Rogers.

Fig. 1: A band-tailed pigeon showing signs of infection with Trichomonosis.
Fig. 2: A dead band-tailed pigeon observed during a Trichomonosis die-off in 2012.
Fig. 3: Caseous lesions in the oral cavity of a band-tailed pigeon with Trichomonosis.
Photos by Jeff Cann (Fig. 1) & Krysta Rogers (Fig. 2 & 3).

While this disease can make pigeons sick any time of the year, large-scale die-offs only occur during the winter, in some years. The last series of mortality events were reported in 2012 in California, when up to 10,000 pigeons were estimated to have died between December and March. Recent research by CDFW suggests that these mortality events are more likely to occur in winters with low precipitation, similar to the conditions we’ve been experiencing so far this winter.

So, if you have acorns, be on the lookout for band-tailed pigeons and enjoy watching them comically hang from the branches as they try to reach an acorn. Hopefully, the pigeons will not experience any die-offs this winter. However, if you do happen to see pigeons that appear sick, such as showing signs of weakness, labored breathing, breathing with their bill open, drooling, reluctance to fly when approached, or are dead, you can help by reporting the mortality to the Wildlife Investigations Lab.

If you have any questions, or would like to report sick or dead band-tailed pigeons, contact Krysta Rogers at 916-358-1662.

Band-tailed Pigeon Disease Study

Adult band-tailed pigeon showing the characteristic white crescent and iridescent greenish-bronze patch of feathers on the hindneck. Photo by Gary Kramer, 2008.

Adult band-tailed pigeon showing the characteristic white crescent and iridescent greenish-bronze patch of feathers on the hindneck. Photo by Gary Kramer, 2008.

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
  • disease.

Habitat Loss

An example of typical band-tailed pigeon habitat, oak and mixed conifer forest in Monterey County. Photo by Krysta Rogers, 2011.

An example of typical band-tailed pigeon habitat, oak and mixed conifer forest in Monterey County. Photo by Krysta Rogers, 2011.

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.

An example of a mineral spring used by band-tailed pigeons for drinking water and for sodium. Photo by Krysta Rogers, 2012.

An example of a mineral spring used by band-tailed pigeons for drinking water and for sodium. Photo by Krysta Rogers, 2012.

Food Resources

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.

Acorns on a coast live oak (Quercus agrifolia) in Monterey County, a favoriate wintertime food of band-tailed pigeons. Photo by Krysta Rogers, 2011.

Acorns on a coast live oak (Quercus agrifolia) in Monterey County, a favoriate wintertime food of band-tailed pigeons. Photo by Krysta Rogers, 2011.

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

Remains of at least 4-5 band-tailed pigeons that had been illegally shot and then discarded. Photo by Krysta Rogers, 2011.

Remains of at least 4-5 band-tailed pigeons that had been illegally shot and then discarded. Photo by Krysta Rogers, 2011.

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.

Disease

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.

An example of caseous oral lesions caused by infection with Trichomonas parasites of a band-tailed pigeon. Note how the lesions completely block the passage of food through the esophagus. Photo by Krysta Rogers, 2012.

An example of caseous oral lesions caused by infection with Trichomonas parasites of a band-tailed pigeon. Note how the lesions completely block the passage of food through the esophagus. Photo by Krysta Rogers, 2012.

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.

Research

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.

Krysta holding a band-tailed pigeon that is ready to be released after it was live-trapped, sampled for Trichomonas, and banded. Photo by Jaime Rudd.

Krysta holding a band-tailed pigeon that is ready to be released after it was live-trapped, sampled for Trichomonas, and banded. Photo by Jaime Rudd.

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.

Necropsy being preformed by Krysta on a dead band-tailed pigeon to determine cause of death and disease status. Photo by David Mollel, 2012.

Necropsy being preformed by Krysta on a dead band-tailed pigeon to determine cause of death and disease status. Photo by David Mollel, 2012.

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.

An adult band-tailed pigeon showing signs of infection with Trichomonas parasites. Notice the drooped wings, ruffled feathers, and open-mouth breathing. Photo by Krysta Rogers, 2012.

An adult band-tailed pigeon showing signs of infection with Trichomonas parasites. Notice the drooped wings, ruffled feathers, and open-mouth breathing. Photo by Krysta Rogers, 2012.

A freshly dead band-tailed pigeon observed during a mortality event due to Trichomonosis. Photo by Krysta Rogers, 2012.

A freshly dead band-tailed pigeon observed during a mortality event due to Trichomonosis. Photo by Krysta Rogers, 2012.

Remains of a band-tailed pigeon that died and was scavenged during a mortality event due to Trichomonosis. Photo by Krysta Rogers, 2012.

Remains of a band-tailed pigeon that died and was scavenged during a mortality event due to Trichomonosis. Photo by Krysta Rogers, 2012.

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.

Collection of an oral swab from a live-trapped band-tailed pigeon for the culture of Trichomonas parasites. Photo by Diana Rickey, 2011.

Collection of an oral swab from a live-trapped band-tailed pigeon for the culture of Trichomonas parasites. Photo by Diana Rickey, 2011.

Uncertain Future

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.

Adult band-tailed pigeon (Patagioenas fasciata monolis) showing the black band on the tail feathers for which this species was named. Photo by Becky Maher, 2011.

Adult band-tailed pigeon (Patagioenas fasciata monolis) showing the black band on the tail feathers for which this species was named. Photo by Becky Maher, 2011.

If you have any questions about the project, or would like to report band-tailed pigeon mortality, contact Krysta Rogers at 916-358-1662.

Be Careful with Our Feathered Friends

By Krysta Rogers and Stella McMillin


A few weeks ago, our avian disease specialist, Krysta Rogers, was notified of an ongoing incident in Kern County. A man reported finding two to five dead birds at a time near his bird feeder over a period of weeks.  This added up to 30 to 50 birds in total, most of which were mourning doves.

Often, mortality occurring near bird feeders is disease-related. Bird feeders can unnaturally congregate birds, increasing the chances of disease transmission. In particular, mourning doves are highly susceptible to a parasite that causes a disease called Trichomoniasis. This disease can lead to significant mortality of mourning doves; it tends to occur during the spring in doves that visit bird feeders.

However, in this incident a raptor and the neighbor’s dog also had died in the same location and a similar scenario had occurred the previous year. As such, this incident seemed to be more likely related to a toxin, rather than disease.

Our pesticide specialist Stella McMillin became involved to investigate the cause of death. Fortunately, Krysta and Stella were able to examine two doves that died during this incident.

Examining the doves, they found no evidence of disease. However, when they looked in the birds’ crops we found both of them full of the same milo seed-like material.  They showed a picture to the Kern County Agricultural Commissioner’s Office who suggested that it appeared to be strychnine bait.  So, they submitted the bait and livers from the birds to a diagnostic lab to test for strychnine and the results were positive.

Strychnine is used to control pocket gophers and is only legally applied underground to prevent exposure to non-target wildlife.  In this case, unless these doves had been using shovels, it appears that the application was not done properly.  Some formulations of strychnine are restricted only to those with applicator’s licenses but others are available to the general public.  Sometimes the general public is not aware that “the label is the law” – it is illegal to use a pesticide in a manner not specified by the label.  When a pesticide, particularly something toxic to vertebrates like strychnine, is not used properly, it poses a hazard to wildlife, pets and children, so investigation of these cases is important.

Now the difficult part begins – identifying the source of the strychnine and taking action to ensure that this situation does not occur again.

Although this incident was not related to disease, it is a reminder, that bird feeders, hummingbird feeders, and bird bathes, should be thoroughly cleaned at least once a week to reduce the chances of spreading disease.

For more information about how to keep birds healthy at bird feeders visit the National Wildlife Health Center (http://www.nwhc.usgs.gov/publications/fact_sheets/coping_with_diseases_at_birdfeeders.jsp) and Audubon (http://web4.audubon.org/bird/at_home/bird_feeding/feeder_maint.html).