Field Protocols
ESTABLISHMENT OF NEST SEARCH PLOTS
Field Protocol Menu
Program Overview
Where To Look
Methods
Data Sheets
Establishing Study Plots
Finding New Nests
Monitoring Nests
Summarizing Nest Fate
Describing Nests' Locations
Measuring Vegetation
Point Counts
Measuring Weather
References
Appendix of BBIRD Variables
General Protocol (PDF)
Grassland Protocol (PDF)
Number and Size of Plots per Site
Each geographic location and habitat condition or type where an independent study is being conducted will be referred to as a SITE. At each site, a sufficient number of nest plots should be established to find at least 20 nests per treatment/habitat type each year, for each of the most locally common species. In eastern hardwood forest this is typically about eight 35--50 ha plots, while in more productive (e.g., western riparian) sites, four 10--20 ha sites might be sufficient. Estimates of nesting success based on fewer than 20 nests may not be reliable (Hensler and Nichols 1981). When setting up a new BBIRD site, location of plots must be identified using a random or stratified random selection process, although constrained sampling may be used to control for aspect, slope, distance to roads, or other similar effects. Great caution must be exercised in terms of multiple objectives. Incorporation of additional treatments (fragments, land management programs, grazing, etc.) can fragment sample sizes. Additional objectives should be addressed by adding nest plots rather than by fragmenting the sample.
There are few specific requirements for plot size and number, but the following guidelines should be followed when determining the size and number of plots:
- Nest plots should be a minimum of 200 x 200 m (4 ha) in size because point count survey locations need to be completely nested within the area searched for nests (survey points should be at least 100 m from the edge of the nest search plot). Small plots are attractive because a larger geographic area can be sampled but search efficiency declines as travel time increases between plots.
- Large numbers of nests can be found in a big plot and search efficiency increases up to a point, but the number of plots that can be searched and monitored drops rapidly as plot size increases. The percentage of nests found also declines in large plots, so there is a trade-off between search efficiency and search intensity. The potential for site-specific bias increases when only a few plots are sampled, reducing the power of inference to areas beyond the plots. It can also be difficult to fit large plots into a single habitat type. Moreover, when plots represent treatments (i.e. grazed vs. ungrazed plots), a sufficient number of plots are necessary to get within and between treatment variance estimates.
Choosing Plots
Plots must be chosen using a random-selection procedure so that inferences can be made to the entire site from the data collected. However, stratifying your site with respect to important features can improve precision. Obviously habitat type has a strong effect on the bird community, but within a general habitat type (e.g., Ponderosa pine) there are many other factors that influence habitat suitability. For example, aspect and proximity to roads or other anthropogenic factors can also influence species composition, density, and productivity. Before selecting plots, give careful thought to factors that might influence bird productivity in your area. Prior to actual choice of plot locations, your randomization scheme should be approved by BBIRD staff. In general, plots should be oriented to maximize local heterogeneity within the plot by running the long axis of each plot perpendicular to any obvious habitat gradient. This will minimize variance among plots.
Also, try to the extent possible to spatially separate the plots from each other, in order that the plots can be treated as independent sampling units. Separate plots cannot share a common boundary.
Plot Shape
Plots can be of any shape, but the borders should be well defined so the area searched for nests can be accurately determined. Plots should be large enough to fit bird survey points (50 m fixed radius plots) completely within the area searched for nests. Survey points should be separated by 200m and all points should be at least 100 m from the edge of the plot (minimum plots width = 200 m; see figure, below).
FIGURE: PLOT SHAPES AND LOCATIONS OF POINT COUNTS
Marking Plots
Permanent markers should be established at 50 m intervals in a grid system to provide reference points for relocating nests; you may want to add additional markers between the 50 m marks if vegetation is dense and distant markers difficult to see. Permanent grid markers are hereafter referred to as stations. Station markers are used as field references for relocating nests, but are also used as reference points for calculating nest locations as UTM coordinates for use with GIS systems. All cooperators should try and gain the use of a GPS (Global Positioning System) unit to accurately locate their plots. (We do have limited access to some GPS units -- contact Tom Martin if you need a unit.) The GPS units we have access to have a minimum error
ranges of +/- 10 meters. This is great for locating plots within a larger geographic area but is not sufficient to accurately locate stations within a plot. We suggest GPS units should be used to locate 1 station on each plot: UTM locations of all other stations can then be calculated from distance and compass bearings from the measured point. Nest locations can be calculated in a similar way using distance and bearings from known station locations. Please note that station locations, and hence nest locations, will only be as accurate as the survey work used to establish stations in the first place. With good survey work, extrapolating from one GPS location per plot will result in more internally accurate locations than locating each station with the GPS unit.
Field Protocol Menu
Program Overview
Where To Look
Methods
Data Sheets
Establishing Study Plots
Finding New Nests
Monitoring Nests
Summarizing Nest Fate
Describing Nests' Locations
Measuring Vegetation
Point Counts
Measuring Weather
References
Appendix of BBIRD Variables
General Protocol (PDF)
Grassland Protocol (PDF)
It is important that stations be well marked, and that they survive between years. If possible, all stations should be permanently marked with wooden or metal stakes. Be sure to get permission from the appropriate landowners or agencies before establishing these permanent markers.
Field Protocols
Last modified: Sunday, 23-March-97 12:20:57 MST