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March 13, 2007

Año Nuevo Birds: Tracking The Northern Harrier

There's a certain paradoxical quality to watching wildlife. Animals can be both predictable and extremely unpredictable.

I've taken many walks in Año Nuevo State Reserve. I like to show up early, and be the first one on the trail, brushing the night's spider webs from the path. The earlier the better, for the school trips that show up later in the morning scare much of the wildlife from the trails.

Just before the ranger station, I enter a great field where inevitably, the male and female Northern Harriers or Marsh Hawks, will be waiting. If I'm lucky, a harrier will still be perched close to the ground and I'll get to watch as it takes off and soars over the fields, looking for breakfast.

I see them every single morning I walk there, but I can never predict where they will be or what they will be doing. Every day is different.

Considered one of the most agile raptors on the continent, the Northern Harrier range extends from Alaska to the Baja coastline. Once common, the species was listed on Audubon's American Birds' Blue List during the 1970's due to habitat loss and the use of pesticides like DDT which had caused especially acute reproductive failure in the species. Basically, DDT caused bird egg shells to be too thin, and the effects of the pesticide were magnified by each level in the food chain, so apex predators like birds of prey were accumulating the largest amounts of the chemicals.

The Blue List tried to provide an early warning of those North American bird species undergoing population or range reductions. The idea was to watch for declines and identify them before species reached endangered status, when it was often too late. The Blue List was published from 1971-1986 in the Audubon Society's American Birds magazine. Flaws in the Blue List certainly existed, and the Audubon Society eventually came up with it's current WatchList system.

The severe population declines noted for Northern Harriers and Short-eared Owls in the late 1970s was attributed to the extensive alteration and loss of grassland habitats throughout the Midwest. Interestingly, although Harrier numbers began to increase in the late 1980s and early 1990s, Short-eared Owl numbers continued to decline. During this same period, there was a substantially large increase in the amount of available grassland habitat due to the Conservation Reserve Program (CRP). Consequently, Northern Harriers appear to benefit from CRP land, while Shorteared Owls may not.

More At: Audubon Society: American Birds - The 102nd Christmas Bird Count

The Northern Harrier population has since begun to recover and is considered stable globally, although some specific populations, especially in New England, remain listed as endangered or threatened at the state level. Still, the Northern Harriers face threats.

A ground nesting bird, the Northern Harrier needs nice marsh to build its nest. Invasive plants like pepperweed threaten this habitat. Native to southern Europe and Western Asia, pepperweed competes with native flora, posing a serious threat to native wetlands and wetland restoration projects. Willows and Cottonwood trees, for example, suffer because they cannot compete effectively against dense stands of pepperweed. Native marsh birds, like the Harrier, therefore do not have the nesting materials needed nor can they nest in the invasive weeds. Research is just beginning on how to protect wetlands from invasives like pepperweed, and a lot of questions remain unanswered.

Northern Harrier Año Nuevo State Reserve

Posted by sorsha at March 13, 2007 7:49 PM