Birds and Disease Transmission
When I’m out photographing birds, I have plenty of down time to watch and think about the complex relationships and interactions between birds and other species. Recently, I was very interested to read about how Northern Cardinals indirectly help reduce the spread of West Nile disease.
Northern Cardinals (along with most other birds) play an essential role in the transmission of disease to humans. When a female mosquito successfully pierces a bird’s skin to probe for blood vessels, suck blood and then leave behind saliva, that bird will become a host to any viral infections carried by the biting mosquito. The infected bird will then spread the infections to the next mosquito who pierces her. Eventually down the line, an infection carrying mosquito will transfer the virus to a human.
How Northern Cardinals Fit In
Some species of birds don’t offer the same quality disease spreading services for blood sucking insects.
Epidemiologists at the CDC claim that when virus carrying mosquitos feast on the blood of Northern Cardinals and infect them with West Nile Virus, the virus does not circulate in that species bloodstream at the level required to transmit the disease to the next mosquito host. Scientists surmise that this disease can be slowed or even halted by an unaccommodating bird host like the Northern Cardinal. Fewer infected mosquitoes means fewer transmissions to humans. (NOTE: Other species of birds that may also suppress this disease are Northern Mockingbirds, Gray Catbirds, and Brown Thrashers.)
So the proliferation of West Nile disease (in the U.S. since 1999) depends on which birds are infected. To make this phenomenon even more fascinating, epidemiologists are finding that the appetites of mosquitoes change mid summer so they are more likely to choose to take their blood meals from poor hosting species like Cardinals, thereby slowing down exposure to humans.
Photographing Northern Cardinals
Northern Cardinals are one of the most common year-round residents in our yard. They are cautiously bold and curious, perching on or around the bird feeders near the windows to forage. No other bird in our yard is as easy to approach with a camera. When I make plans to photograph Cardinals, there is little need for me to venture outside with my camera and become a blood meal for mosquitos and ticks.
It’s the coloration of the female cardinal that I find most eloquent. Subtle olive brown feathers are tinged with red on the crest, eyebrows, wings and tail. Her bold red/orange cone shaped beak matches the male cardinal’s beak, but appears less protuberent against the more understated colors of her face.
When I took the photo above, the sky was almost completely covered with sun obscuring clouds, making for a bright but diffused light. Diffused light softens the contrasts across the whole image, making for a more even and balanced look. This type of light creates less of a distinction between the shadows, highlights and mid-tones.
Showy Bird Crests
When focusing in on a female Northern Cardinal, I normally try to include a capture with her crest held high. If she notices the camera, her crest generally goes down, perhaps an effort not to be detected. When a bird sports a crest, she can raise and lower it to indicate mating readiness, nervousness, excitement, caution, and fear. These upright barbs high on the bird’s crown are made of soft, bendable fluffy feathers which can be raised high in a perky salute or tucked back smoothly on the head. Nestlings and newly fledged Cardinals often display still growing crests that look more threadbare.
To view photographs of Northern Cardinals engaged in courtship feeding, press this link.