The Skagit Flats Winter Hawk Count -

Methods

Observation and Recording

The census is carried out by about 100 volunteer observers during a two-hour period (from 9am to 11am), usually on a Saturday morning in mid-February. All the observers have been through the FRG's raptor identification class or are otherwise experienced in raptor identification. The observers are organized into teams, varying from two to six people, and each team is assigned a route.

The census area is divided into 27 routes* and each is surveyed once during the two-hour census period. The procedure is typically as follows:

  • starting at 9am, drive to first observation point
  • get out of car
  • scan 360° with binoculars and record details of all raptors seen
  • use a scope to identify far-off or questionable birds
  • if a bird is flying, note the direction of flight
  • drive to next point
  • etc.
  • complete the route by 11 am

The location of each bird is marked on a map, along with the following information:

  • species (using the AOU 4-letter codes, e.g. BAEA for Bald Eagle)
  • type of perch and, if flying, an arrow to show direction of flight
  • age and sex, if discernable and as appropriate for the species – for example: Bald Eagles can be classified as juvenile, sub-adult, or adult, but are not differentiated male from female.

The teams meet afterward, traditionally at the Breazeale Interpretive Center at the Padilla Bay Reserve, and the results are tallied.

Team leaders count how many of each species they marked on the map, and total their observations on a tally sheet. They then cross-check by counting the dots on their map. They take care to avoid duplication for birds flying from one area to another, or recorded near the boundary between areas – in these cases the team leaders confer and make sure the bird is not counted twice.

Species totals for each route are tabulated on a large white-board at the Center and an overall picture of the morning's census is constructed. By 1pm or so the last teams have completed their tallies. Then everyone goes off to see any rarities reported.

* There were 28 routes prior to 1993 when two were combined (24 and 25 became just 25).

Data Entry and Validation

The observations from all 15 years of the census have been entered into The Nature Conservancy's GIS (Geographic Information System). Sue Clark, a Nature Conservancy volunteer, digitized each bird location and entered the details - species, age, etc. She checked for errors by comparing a summary report from the GIS data to the tally sheets, looking at the totals for each species on each route in each year. Where there were discrepancies she compared the points in GIS with the dots on the team's maps, and made adjustments as required - sometimes amending the GIS data, and sometimes correcting an inaccurate total on a tally sheet.

Pat Little, who is an FRG volunteer and used to work for TNC, reviewed the data after Sue completed her review, checking overall data consistency and validity. He exported the data to a spreadsheet and analyzed it:

  • if any codes were by themselves invalid (i.e., not one of the permitted codes) he looked up the data point in GIS, consulted the original map, and made corrections to the GIS data as appropriate;

  • he looked to see if the combinations of codes were reasonable, to make sure information that cannot be readily seen in the field is not included (e.g., if a sex is given for Bald Eagles, since the sexes cannot be distinguished) – in these cases he removed any invalid information.

Pat used the GIS to create the maps on this CD and Excel for the graphs.  


 
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