When Angela听Theodosopoulos began studying听Colorado's听Mountain and听Black-capped Chickadees four years ago, her original goal was to research听hybridization among the species and听the听various parasites they each听co-evolved with. But when the PhD candidate at the University of Colorado Boulder听began analyzing the birds' blood, she made a worrisome discovery: Some of the chickadees听were infected with a听strain of introduced听avian malaria.
According to a听听颈苍听Biology Letters,听Theodosopoulos' finding听is听the first record of this particular听strain in a non-migratory bird species in North America. The parasite was found in two Mountain Chickadees and a single Black-capped Chickadee, but the听low number of infections makes听Theodosopoulos, lead author of the paper,听believe听that another avian species might be the main host. While the strain has the potential to be damaging to bird populations,听Theodosopoulos stresses that听more research is needed.
鈥淚 definitely would not panic at this point,鈥澨齭he听says. 鈥淏ut it is important to think about it and to understand it, because it is a very invasive parasite, it can cause disease, and it has been associated with population declines in other places. We just don't know if that's going to be what happens here.鈥�
Avian malaria is caused by a parasite that听听and听is spread via mosquitoes.听Though some cases of avian malaria are mild or asymptomatic, infected birds can听experience a loss of red blood cells, lethargy, a shortened life span, or in extreme cases, convulsions or death.
The strain found in Boulder is called SGS1, named for the species it was first identified in: a Sudan Golden Sparrow in 2002. Generally speaking,听genetic variation in parasites leads to different strains of the disease, which tend to听infect species in different geographic areas. But when a strain reaches birds that haven't encountered it before and are not adapted to fight it, 鈥渋t can cause much harm to the population,鈥� says Staffan Bensch, professor of animal ecology at Lund University in Sweden and co-author on the paper.听Researchers can鈥檛 say yet how North American birds will respond to SGS1, but in London, SGS1 has been听.
The fact that the parasite has听infected听non-migratory听chickadees听is听concerning because it's听鈥渁 sign that it is already spreading,鈥� Theodosopoulos says. A migratory bird can be infected anywhere along its journey, but the听chickadees had to听have contracted the disease locally. Until now, the only recorded North American birds with SGS1 were captive birds in New York and one wild, migratory tree swallow in Canada. Theodosopoulos speculates mosquitoes may have spread the disease from infected birds in zoos, which could have contracted it before they were imported.听
鈥淢any of them recover in captivity,鈥� Bensch says. 鈥淏ut in the wild, such a bird is very easy prey for a raptor.鈥�
Next, the researchers want to find out if SGS1 really is more prevalent in another local species鈥攁nd which one. They think it could听be House Sparrows, given the high infection rate of that species in Europe and their large populations in urban areas. Theodosopoulos hopes to discover if and when SGS1 infected House Sparrows in Colorado and, afterward, learn what other species it may have reached.
To do so, she partnered with Dr. Garth Spellman, curator of ornithology at the Denver Museum of Nature &听Science. Spellman听has a collection of tissue samples from House Sparrows from the Denver metropolitan area dating back 10 years. Incidentally, a paper published approximately a decade听ago found no instances of SGS1 in House Sparrows in the Colorado Front Range, a mountain region including Denver and Boulder. So, Spellman and Theodosopoulos believe that if SGS1 has infected House Sparrows, it likely did so in the past听10 years.
鈥淲e can look at 20, 30 birds every year for the last decade to see if we can find SGS1,鈥� Spellman says. 鈥淚f so, we might be able to chronicle the year that it arrived in the Front Range.鈥� Based on the prevalence of SGS1 in those samples, they could also estimate how common it is in House Sparrows today.
This future research will be crucial to understanding the extent of risk to North American birds. If SGS1 is found at a high rate in Colorado鈥檚 House Sparrows, Spellman believes that would be a sign that House Sparrows in metro areas nationwide are infected. Moreover, a high presence of SGS1 in urban birds might increase the chances of avian malaria spreading to birds outside cities.
鈥淚n Denver, it could be particularly important, because we have a number of grassland species, for example, that could be exposed right at that urban-wildland interface,鈥� Spellman says. Already,听. 鈥淚f just one of those species is exposed to a novel pathogen, that could have dire consequences.鈥�
For now, it鈥檚 a waiting game as scientists gather more information. If, theoretically, researchers find SGS1 in other places in the country, if dead birds test positive for SGS1, and if the birds that carry SGS1 start having negative health impacts while uninfected individuals don鈥檛, then听this strain would be听something to really听worry about, Theodosopoulos says.听
Even if SGS1 winds up not causing any major issues for North American birds, as the paper notes, the appearance of this strain is yet听another reminder of the human听impact on the environment and the need for diligence in a more globalized world.听鈥淲e're changing the habitat; we鈥檙e moving species around,鈥� Theodosopoulos says. 鈥淭his certainly plays a role in the way that parasites and their diseases are able to spread.鈥�
