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Urban Sprawl Contributes to Illness in Songbirds

April 07, 2014 | 3,303 views
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By Dr. Becker

Researchers at Arizona State University made a startling discovery while studying a lovely little songbird called the wild house finch. The researchers set out to investigate intestinal parasites and the canarypox virus in the birds, along with the effect of spreading urbanization on the birds' stress response system.1

What they discovered, according to Science Daily, is a first:

"Humans living in densely populated urban areas have a profound impact not only on their physical environment, but also on the health and fitness of native wildlife. For the first time, scientists have found a direct link between the degree of urbanization and the prevalence and severity of two distinct parasites in wild house finches.

"Loss of natural habitat may be a driving force behind increases in avian parasite infections."

Wild house finches inhabit the desert southwest in the U.S., and are also now found throughout North America. Adult male birds are five to six inches long. They have a bright red, orange or yellow crown, breast and rump feathers.

Researchers Measure Effects of Urban Sprawl on Male House Finches

The team of researchers studied male house finches at multiple locations throughout Maricopa County in central AZ. Each location (a total of seven) was different in terms of the number of people living within about a half mile. The number of residents ranged from around a dozen to more than 17,000.

The researchers evaluated a total of 13 different urbanization factors, including soil disturbance and cultivation. They also weighed the potential connection between oxidative stress, the level of urbanization, and parasitic infections to determine if increased rates of infection correlated with increased stress levels in the house finches.

One of the ASU researchers, Mathieu Giraudeau, in an interview with Science Daily, pointed out that:

"Several studies have measured parasite infection in urban animals, but surprisingly we are the first to measure whether wild birds living in a city were more or less infected by a parasite and a pathogen, as well as how these infections are linked to their physiological stress."

Birds in Urban Areas Tend to Be Heavier, and Heavier Birds Have More Parasites

Natural habitats and ecosystems have been radically altered to accommodate urban sprawl. Current estimates are that over half the world's population now lives in cities.

There is growing concern about the spread of diseases from urban wildlife to humans. Studies suggest that perhaps 75 percent of the world's emerging infectious diseases are zoonotic, meaning they can be passed from animals to humans.

There is also concern that wild animals living in or near urban areas are acquiring multiple types of diseases, and scientists are now investigating cause and effect. Are urban animals suffering from compromised immune systems and therefore are less able to fight off infections? Or are they acquiring more disease through increased contact with other infected animals?

The ASU team learned that GI parasitic infections in birds are higher in urban areas where the soil is compacted and vegetation is cultivated. Birds from locations with more cultivated vegetation are heavier, and heavier birds are significantly more infected by parasites than smaller birds. The parasites, called coccidians, inhabit a bird's gut and interfere with nutrient absorption.

Study Concludes Loss of Natural Habitat Contributes to Avian Parasitic Infections

The researchers also found that the number of house finches with poxvirus infections was greater in more urbanized areas. I have found this to be true as a wildlife rehabilitator as well; I have more poxvirus positive birds coming to me from cities vs. more rural communities. The researchers did now, however, find a connection to oxidative stress. The avian poxvirus causes wounds on the feet, eyes, ears and wings. As the disease progresses, the lesions bleed and crust over and can lead to the loss of digits.

The ASU study authors determined that decreases in natural habitat may be a major contributor to increasing levels of avian parasite infections, and the same may be true in other animals.

The authors' conclusion:

"These results indicate that the physical presence of humans in cities and the associated altered urban landscape characteristics are associated with increased infections with both a virus and a gastrointestinal parasite in this common songbird resident of North American cities.

"Though we failed to find elevations in urban- or parasite/pathogen-mediated oxidative stress, humans may facilitate infections in these birds via bird feeders (i.e. horizontal disease transmission due to unsanitary surfaces and/or elevations in host population densities) and/or via elevations in other forms of physiological stress (e.g. corticosterone, nutritional)."

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