Posts Tagged ‘Winter Ecology’

Yesterday I, my wife, and our ten-day-old daughter went out to bird the area south of Davis, CA. as part of the Winter Raptor Survey that has been started by the Hawk Migration Association of North America (HMANA).  I am on the HMANA board of directors and have been helping to organize this winter raptor survey.  We are hoping it will grow into a nation-wide monitoring system of the raptors that spend the winter months anywhere in North America.  To run a survey route all that is need is a bit of local raptor knowledge and four days a year.  Each volunteer sets up their own route in an area, and then drives that route one day in November, one day in December, one day in January, and one day in February.  After driving the route (which should be between 30 and 100 miles long), and identifying all the raptors seen, the results are entered into an online database and compiled.  Repeatedly surveying the same route several times each winter gives a better measurement of how many individuals and species are using a particular area, and will result in a more accurate overall population estimate.

The route that I am running was established by a former graduate student in the Avian Sciences Graduate Group at U.C. Davis that he used for his masters research (he established many routes throughout California, so if anyone wants to run an established route, contact me).  This route works its way through an area land that is used for crops, orchards, and cattle and sheep range land.  It is about 40 miles long and took us about 4 hours to run (12 to 4). The day was a bright and sunny one with no clouds and a cold wind out of the northwest.

It was a wonderful day of birding, and my daughter’s first birding outing!  She slept in her car seat the whole time except when we stopped to feed her and change her diaper.   In total, we saw 96 raptors of 10 species.  The species were Turkey Vulture, White-tailed Kite, Northern Harrier, Cooper’s Hawk, Red-tailed Hawk, Ferruginous Hawk (a beautifully marked adult), American Kestrel, Merlin, Peregrine Falcon, and Prairie Falcon.

Other birds we saw included Loggerhead Shrike, Savannah Sparrow, White-crowned Sparrow, Golden-crowned Sparrow, American Pipit, Least Sandpiper, Killdeer, Cattle Egret, Great Egret, Great Blue Heron, American Crow, Common Raven, Mallard, Brewer’s Blackbird, Red-winged Blackbird, Double-crested Cormorant, and European Starling.

I am already looking forward to January’s survey!

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This month marks the end of my first year serving on the board of directors of The Hawk Migration Association of North America (HMANA).  HMANA is an organization that is serving as a central clearing house of raptor migration data across the continent.  Member sites upload the count data they have collected, and HMANA sorts it and makes it open and searchable to anyone who is interested.  HMANA also analyses and presents much of the data it collects in their journal, Raptor Migration Studies.  Other than migration counts, HMANA has also been working on a project called the Raptor Population Index which is attempting to track the population status of all of North America’s raptor species.  Yet another HMANA project, and one that I have been helping with a fair bit, is the Winter Raptor Survey.  What we want to set up is a network of survey routes that are run each year and that will allow us to monitor the wintering population of birds of prey in North America.

Winter marks a poorly studied part of the annual cycle in the lives of birds of prey.  Where raptors spend the winter, how many there are, and what they are doing are all questions that have, at best, only general answers.  The studies that have been done have given some very interesting and important results.  In Argentina in the mid-1990s, there were reports large numbers of  Swainson’s Hawks being found dead at their communal roost sties.  In 1995 and 1996 some 6,000 Swainson’s Hawks were found dead at such roosts.  The cause was determined to acute pesticide toxicity.  Since Swainson’s Hawks feed largely on insects during the winter, they were being poisoned when they eat insects that had been sprayed with highly toxic chemicals, or were being sprayed directly when they were perched on the ground in crop fields being sprayed.  Specifically, an organophosphate called monocrotophos proved to be especially deadly to raptors.  This chemical had already been banned in the USA, and the deaths of the an estimated 20,000 Swainson’s Hawks led to the banning of this chemical in Argentina in 1999.  A different study on the winter ecology of raptors that was conducted here in central California found that male and female American Kestrels use different habitats to hunt.  Females generally use the more productive open grassy territories, while males are generally relegated (probably due to their smaller size) to less productive mixed shrub habitats.  Such habitat partitioning is vital to know if conservation is gong to be effective.  If a declining species displayed a similar habitat partitioning, and only one habitat type were known and conserved, the population would still decline.

So, how is the HMANA Winter Raptor Survey hoping to monitor the winter populations of birds of prey in North American?  The goal is to establish survey routes that are run once a month for the four months (November, December, January, and February).  This span of time covers the ‘winter’ months of most raptor species.  Along the routes, which are between 30 and 100 miles long, the habitat is described according to one of the categories we have established and the position and identification of all raptor species seen along the route are recorded.  This survey data is then uploaded to the WRS website.  This data can then be used to track habitat use, landscape and habitat change, raptor numbers and densities, and the interactions between any and all of the above.  So, to all the raptor-philes out there, we need your help!  Now that the fall migration is over, please lend a hand in monitoring raptors in the winter.  Set up a route!

HMANA is largely volunteer run.  Check out the HMANA webpage at http://www.hmana.org/ for general HMANA information and news, and the HMANA WRS webpage at http://wrs.hmana.org for specific details on how to set up and run routes.  While you are at these websites become a member of HMANA!  It is a great organization that is showing what citizen scientists can do on continent-wide scale.

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