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|Ground counts of shorebirds at non-breeding sites|
Important preliminary notes
Important preliminary notes
In 2001, the Canadian Shorebird Working Group and the U.S. Shorebird Research and Monitoring Working Group developed the Program for Regional and International Shorebird Monitoring (PRISM). PRISM now serves to coordinate other shorebird monitoring programs in North America, including the International Shorebird Surveys (ISS), the Western Shorebird Survey (WSS), the Maritimes Shorebird Survey (MSS), and others, as well as monitoring programs still under development. The primary goals of PRISM are to: estimate the population sizes and trends of shorebirds that regularly breed in North America (see species list below); describe their distribution, abundance, and habitat relationships; monitor their numbers at stopover locations; and assist local managers in meeting their shorebird conservation goals. PRISM does not supercede other shorebird survey programs; rather it seeks to coordinate with and build on existing programs and initiate new approaches that address monitoring needs not being met. A detailed overview of PRISM (Bart et al. 2002) is available at: http://wss.wr.usgs.gov/data/PRISMOverview_01.doc (this links to a Microsoft Word document).
The reasons for initiating shorebird monitoring vary from a need to monitor the effectiveness of local Adaptive Resource Management (ARM) to estimating global sizes and trends of shorebird populations. Generally, ARM and associated effectiveness monitoring takes place at a local scale -- a single site or management district (e.g., a wildlife refuge or wetland management district). Single-site monitoring projects are also useful for describing species composition, temporal patterns of use, and shorebird-habitat relationships at that site. However, monitoring trends of regional or global shorebird populations must take place at much larger scales (i.e., many sites across the entire region in question). The length of a monitoring project is also determined by your monitoring goals. Effectiveness monitoring for ARM and other site-specific needs often may be accomplished in a relatively short period of time (e.g., several seasons or years), whereas tracking population trends requires long-term monitoring (e.g., decades). Thus, it is important to determine what your survey goals are before you initiate your survey project.
If your monitoring goals are specific to a single site or management district, then defining your study site should be dictated by those goals. For example, say you want to determine whether 10 new dredge islands created at wildlife refuge will attract a greater nesting density or productivity of Least Terns than what had been observed on the refuge's 10 existing (but highly vegetated) natural islands. In this scenario, your study area would be the new and old islands.
If, however, your goals are to estimate population sizes or trends of shorebird species that migrate through your region, then site selection needs greater consideration. This is particularly true for inland regions (e.g., the Prairie Potholes), where weather patterns significantly influence the availability and location of shorebird habitats from season to season and year to year. For example, higher-than-normal precipitation may inundate all shorebird habitat at 'known shorebird sites' (usually permanent and semi-permanent wetlands), in which case shorebirds may disperse widely across the landscape to flooded fields and other ephemeral wetlands. In this scenario, monitoring only the 'known shorebird sites' could result in entire years - even a decade or more - of few, if any, shorebirds counted, even though their population trends may be perfectly stable.
If you wish to dovetail your single-site surveys with regional population assessments or participate in large-scale population monitoring, we strongly suggest that you coordinate your site selection (and survey timing) with PRISM, ISS, WSS, MSS, and/or other existing survey programs. Shorebird species that breed in North America and warrant long-term monitoring are listed below. If you would like help with identifying a site for monitoring or have a site in mind that you would like to have included in PRISM, please contact Jon Bart at email@example.com. The information gained and the overall value of any survey program can be maximized by linking regionally with other sites.
Monitoring shorebirds during the non-breeding season (migration and winter) can yield information useful for many purposes, including effectiveness monitoring for ARM and describing shorebird-habitat relationships, species composition and phenology. Furthermore, many shorebird species breed in relatively inaccessible locations, thus monitoring them at migration stopover sites and/or wintering areas can serve as an 'early warning system' for populations that may be declining and warrant further investigation.
Pluvialis squatarola, Black-bellied Plover; Pluvialis dominica, American Golden-plover; Pluvialis fulva, Pacific Golden-plover; Charadrius alexandrinus, Snowy Plover; Charadrius wilsonia, Wilson's Plover; Charadrius semipalmatus, Semipalmated Plover; Charadrius melodus, Piping Plover; Charadrius vociferus, Killdeer; Charadrius montanus, Mountain Plover; Haematopus palliatus, American Oystercatcher; Haematopus bachmani, Black Oystercatcher; Himantopus mexicanus, Black-necked Stilt; Recurvirostra americana, American Avocet; Tringa melanoleuca, Greater Yellowlegs; Tringa flavipes, Lesser Yellowlegs; Tringa solitaria, Solitary Sandpiper; Catoptrophorus semipalmatus, Willet; Heteroscelus incanus, Wandering Tattler; Actitis macularia, Spotted Sandpiper; Bartramia longicauda, Upland Sandpiper; Numenius tahitiensis, Bristle-thighed Curlew; Numenius phaeopus, Whimbrel; Numenius americanus, Long-billed Curlew; Limosa haemastica, Hudsonian Godwit; Limosa limosa baueri, Bar-tailed Godwit; Limosa fedoa, Marbled Godwit; Arenaria interpres, Ruddy Turnstone; Arenaria melanocephala, Black Turnstone; Aphriza virgata, Surfbird; Calidris canutus, Red Knot; Calidris ptilocnemis, Rock Sandpiper; Calidris alba, Sanderling; Calidris pusilla, Semipalmated Sandpiper; Calidris mauri, Western Sandpiper; Calidris minutilla, Least Sandpiper; Calidris fuscicollis, White-rumped Sandpiper; Calidris bairdii, Baird's Sandpiper; Calidris melanotos, Pectoral Sandpiper; Calidris maritima, Purple Sandpiper; Calidris alpina, Dunlin; Calidris himantopus, Stilt Sandpiper; Tryngites subruficollis, Buff-breasted Sandpiper; Limnodromus griseus, Short-billed Dowitcher; Limnodromus scolopaceus, Long-billed Dowitcher; Gallinago delicata, Wilson's Snipe; Scolopax minor, American Woodcock; Phalaropus tricolor, Wilson's Phalarope; Phalaropus lobatus, Red-necked Phalarope; Phalaropus fulicaria, Red Phalarope
There is no one technique advocated by PRISM for monitoring shorebirds. This is because the techniques used for one site, region, and/or season may or may not meet the needs of, or be suitable in, another site, region, or season. Depending on where your site is located or what your goals are, you may want to use counting and data-collection techniques designed by ISS, WSS, MSS, etc. (see list below under the heading, Existing Programs Employing These Techniques). The techniques we describe in this document are relatively basic, and generally form the basis of any ground-based shorebird counts at their migration stopovers or wintering areas. You may, however, adapt these techniques, or even use alternate methods, to suit your needs.
If a site is small, generally it can be surveyed completely to result in a census of all birds at the site. If, however, the site is quite extensive and/or has habitats of differential suitability to shorebirds, a total census at the site may be impossible. If your goal is to determine habitat use patterns, phenology, or effects of management, a total census may not be necessary. On the other hand, if you want to estimate the number of all birds using a site and/or contribute to a population-monitoring program, you may need to consider more carefully which portions of a study site to survey.
Before initiating a survey, it is useful to conduct a pilot study to estimate the number of shorebird days likely to occur in each habitat type during the survey period in question. A shorebird day is the equivalent of one shorebird spending 24 hours within a given study site during a given survey period. These estimates do not have to be precise; rather, they are meant to help guide where you focus your survey efforts.
Once you have estimated shorebird-days, classify the habitats or sections of your study site as Type 1, 2, or 3 (this PRISM technique is especially important for large-scale monitoring programs). In Type 1 areas, substantial numbers of shorebirds are present during the survey period; Type 2 areas host smaller numbers of shorebirds during the survey period; and virtually no shorebirds are present at Type 3 areas during the survey period. For a given study site the approximate numeric goals in apportioning Type 1, 2, and 3 areas are:
Type 1 areas should receive the greatest portion of your survey effort, Type 2 areas may be surveyed with less frequency, and Type 3 areas do not need regular surveys, but just occasional checks or reports from other observers to confirm that shorebirds do not occur there. For further explanation on use of this approach at the regional scale, please refer to: http://wss.wr.usgs.gov/data/PRISMOverview_01.doc.
Efforts to count all shorebirds (as opposed to sampling) at non-breeding sites are typical. However, detectability, visibility, access, or other factors may preclude a complete census. In this case, you may need to calculate an adjustment or weighting factor for the percentage of birds you are likely to detect -- particularly for population-monitoring programs. Again, a pilot study may be crucial to your success. For the purpose of calculating adjustments or weighting factors, you may be able to overcome access limitations (e.g., areas that cannot be accessed by foot) temporarily by conducting pilot surveys from boats or aircraft. Again, the goals of the survey will dictate whether or not this is necessary. To document shorebird habitat relationships or phenology, partial coverage of sites may be acceptable or even desirable. For more information on adjusting or weighting, again please refer to: http://wss.wr.usgs.gov/data/PRISMOverview_01.doc.
Prepare a detailed description of the study site, including lat-long and delineations of Type 1, 2, and 3 areas (if using this approach). For each of the three Types, also describe: the type and general extent (e.g., hectares) of existing habitats; the exact survey points from which data are collected and the area surveyed from those points; the species/numbers likely to be encountered; and specific tips for carrying out the survey. Also prepare a detailed map, including GPS-derived UTM coordinates when feasible, that shows the study site boundaries; Type 1, 2, and 3 areas; all survey points from which shorebird data are collected; and the area(s) surveyed from a given survey point.
Keep in mind that staff and volunteer turnover occurs often, so you must ensure that descriptions and maps are detailed enough that future surveyors will be able to repeat exactly what previous surveyors did. To that end, be sure to include in the site description and on the map any landmarks, road names/numbers, mileages, signs, etc. that would help someone else find exact locations. Update both site descriptions and maps as needed (i.e., after sudden major changes, natural or man-made, -and/or periodically as gradual changes occur). It is particularly important to document habitat changes if they affect the visibility and/or habitat use of birds in the survey area.
For a given study site, first identify focal species and the survey periods. Focal species may include all species present (e.g., for large-scale population monitoring programs), or they may be limited to one or more species selected to address specific information or management needs. The focal species and/or goals of the study will, in turn, dictate the survey period. If no historical shorebird data are available for your site or region, a pilot study should be undertaken to determine the optimal timing for a given survey period and/or set of focal species. If your study site is in midcontinental North America, expected phenologies are available in Skagen et al. (1999) and at http://www.fort.usgs.gov/shorebirds.
Usually, a survey period during non-breeding season will consist of spring migration, fall migration, and/or a portion of winter, depending on location. Most of these surveys consist of a series of visits conducted at various pre-determined intervals throughout the survey period -- ideally at least once every 10 days during the survey period. Typically, a survey period is at least 30 days long, but it can be shorter or longer, depending on how long it usually takes for focal species to move through the study site. If your surveys are part of regional or global population monitoring, you should conduct surveys according to ISS standards: survey your site at least once every 10 days from April 1 through June 10 during spring migration and from 11 July through 31 October during fall migration. (Surveys conducted less frequently are less useful, but may be helpful in certain analyses. For more information on ISS survey timing, please refer to the ISS website at: http://www.manomet.org/WHSRN/iss.htm.
Determine the factors that are likely to enhance the efficiency and accuracy of survey results. For example, ISS recommends surveying coastal resting sites at high tide (when shorebirds typically gather to rest), and coastal feeding sites at lower tides. Other factors to consider include time of day, direction of the sun, wind velocity/direction, precipitation, etc. Some general guidelines to follow are:
Also determine the factors or conditions that could introduce unnecessary variability (“noise”) in count data (very likely the same type of factors mentioned above), and try to hold them constant over all surveys. For example, if you decide to conduct surveys in the morning only, avoid switching to evening. Decisions about survey timing and acceptable conditions should be made after careful evaluation, including visits to the study site, because changing them after survey data have already been collected will confound those data. Overall, each situation should be evaluated according to monitoring goals and local circumstances.
Before you begin your survey, you should record certain preliminary data that will be useful later during data analyses. The minimum preliminary data needed for ISS are:
You may also choose to record:
After your survey is over, we suggest that you also record the level of human disturbance you witnessed, as it affected the birds you were counting (ISS requests this information). For a list of standardized codes used by the International Shorebird Survey (ISS) to quantify levels of water/tide, survey accuracy, and human disturbance, see the ISS website at: http://www.manomet.org/WHSRN/iss.htm.
If you count shorebirds from more than one survey point at your study site, develop a system for identifying each point, and record the point ID as part of your preliminary data each time you switch survey points. If you plan to enter your data on the International Shorebird Survey (ISS) website, you also should record the lat-long (if known) and distance/direction from the nearest public road found on a road atlas (this information should be part of your site description).
Carefully review bird-identification guides to become familiar with the key characteristics that distinguish all focal species. Knowledge of shorebird migration chronologies, general habitat preferences, sizes/sihouettes and morphometric proportions (e.g., ratio of wing to tail length, or body to leg length), and postures/feeding styles and other behavioral cues is extremely helpful. Be aware that even the best shorebird experts have trouble identifying some species, and there will be times when you will have to make some educated guesses or lump birds into some sort of category (see below). [NOTE: Counts for Long- and Short-billed dowitchers, and for Lesser and Greater yellowlegs, are frequently combined because distinguishing them under most field conditions can be difficult, even for the most-experienced biologist or birder (Stenzel and Page 1988). Vocalizations, however, can provide definitive identifications, so become familiar with their calls as well.]
When you arrive at a given survey point, determine whether binoculars or a spotting scope would be more appropriate or useful. Unless birds are quite close, a spotting scope is usually best. On the other hand, wind can cause a spotting scope to vibrate, thus making binoculars more desirable if they provide the power needed to identify birds.
In some wetlands, particularly small ones, it may be possible to see, identify, and count all shorebirds present from a single survey point. In that case, pick an obvious starting place (e.g., the western edge of the wetland) and gradually scan across the site with your binoculars or scope. As you scan, count and record the total number, one species at a time -- unless there are so few birds that you can count all species at once. Be sure to identify shorebirds to the lowest taxonomic unit possible, including subspecies if known (for more information on subspecies or regional populations, see http://wss.wr.usgs.gov/data/PRISMOverview_01.doc).
Often, there are large numbers of shorebirds milling around continuously, making it very difficult if not impossible to count every bird. In that case, you will need to estimate numbers. In that case, we suggest first dividing the survey area into smaller, more manageable segments naturally delimited by topographic features, such as dunes, pools, variations in vegetation/water/substrate, tidal zones, changes in shoreline geometry, natural or man-made objects, etc. Then count a small number of birds (e.g., 10) to gain a sense of what a group of 10 birds “looks like.” Then count by 10s to 50s or 100 birds to gain a sense of what 50 or 100 birds “looks like.” Finally, count by 50s or 100s to 1000 birds, and so on until you have counted all the birds visible from your survey point. If your survey is for ISS (or some other survey program with standardized protocol), indicate the accuracy level of your counts (i.e., actual count, systematic estimate like that just described, or a ‘guesstimate;’ for denoting accuracy levels, see: http://www.manomet.org/WHSRN/iss.htm).
If you cannot identify each species in a large group, estimate the total number of birds by size class -- i.e., peeps and small, medium, or large shorebirds. A general size-class guideline is:
Again, if your survey is for ISS, you should indicate your accuracy level. For your own study purposes, you may want to extrapolate species numbers using a technique involving by sub-sampling. [However, please note that ISS requests that you record at the species level ONLY birds you actually identified (see below)]. Sub-sampling first entails estimating the overall percentage of each species (or size class) in the group. To estimate percentages, choose several subsets of birds across the group (stratifying by habitat or water depth if necessary), then count and identify all individuals within those subsets (recording your numbers by species) and average the percentages for each species or size class across all subsets. Then use the resulting percentages to extrapolate numbers of each species or size class for the entire group. For example, in four subsets of 30 peeps each, you counted a total of 12 Least Sandpipers (10%), 72 Semipalmated Sandpipers (60%), and 36 White-rumped Sandpipers (30%). If your total count of peeps across the entire group was 2000, your extrapolations to all 2000 birds would yield 200 Least Sandpipers, 1200 Semipalmated Sandpipers, and 600 White-rumped Sandpipers for the entire segment. (In the ISS, you would report 1880 PEEP and your actual counts of the identified species.)
When you finish surveying from a given survey point, move on to the nest one. If you plan to enter your survey data on the ISS website, it is not necessary to report shorebird data separately for each survey point, but we advise that you keep those data separate in your own files.
ISS does not require that you record habitat data at each survey point
or which habitats you find birds using, but they do ask you to fill out
a habitat data form for your site overall (see ISS website for habitat
form at: http://www.manomet.org/WHSRN/iss.htm).
Things that could bias your counts
We have identified three potential sources of bias, frame bias, selection bias, and measurement bias, that could diminish the usefulness of shorebird survey data for population trend monitoring or even generate misleading results. Frame and selection bias occur at the regional level and measurement bias occurs at the site level. Although these three bias issues are most important to consider for population monitoring, we include discussions of them here for your interest and perspective. Measurement error is another concern; it can occur in all types of monitoring and can lead to measurement bias under certain circumstances. We begin with brief descriptions of measurement error and measurement bias, then discuss frame and selection bias.
Measurement error is the difference between the number of birds recorded and the number actually present. The reason for distinguishing measurement error from measurement bias is that measurement error alone does not necessarily cause any bias in trend estimates. Several factors can contribute to measurement error, including the detectability of birds present (often affected by habitat), weather, time of day, time of year, tidal levels, year effects (i.e., drought, flooding, etc.), habitat changes, observer differences, and bird behavior. For example, an observer fails to detect 50% of the birds present (i.e., measurement error), but there is no long-term trend in this detection rate; thus, the long-term trend estimated from the survey is unbiased (i.e., no measurement bias). If, however, the observer is replaced by someone who detects 90% of the birds, measurement bias will result. This is one reason why it is so important to ensure long-term commitment among observers in long-term monitoring projects.
Measurement bias occurs when there is a trend in the proportion of birds recorded at a given site over the course of a survey. For example, during early phases of the survey period, 50% of the birds are not detected due to vegetation that obscures the observer’s view of them, but changes in the vegetation results in 25% more birds detected during latter phases of the survey. The resulting data would indicate an increase in the number of birds using the site even if the number had actually remained stable. Changes in survey methods also often result in measurement bias. One way to avoid this problem is to survey the entire site. If access precludes surveys in some areas, occasionally use alternative methods (e.g., surveys by boat or aircraft) for estimating the number of birds and species using those areas, and adjust survey numbers accordingly. Another factor that can result in not counting all birds present is low detection rates. If this problem is suspected, calculate detection rates and adjust the bird survey data accordingly.
Typically, it is difficult to control all the variables encountered during field studies of any kind, weather and climate in particular. These non-biological sources of variation do not lead to measurement error, per se, but they can add “noise” to the data, thus diminishing their power. Generally, non-biological sources of variation do not introduce measurement bias, and often there is little that one can do to control them anyway. It is important, however, to understand that biases can arise from these sources and how to account for them.
Frame bias refers to the problem of not covering all sites occupied by shorebirds during the study period, or not covering the entire period of interest, and is a concern only in long-term, region-wide population monitoring and in estimating population sizes. To avoid this problem, shorebird surveys must be conducted at sites across the entire region of interest. In addition, site selection must take into consideration whether or not shorebirds are likely to occur at a given site during the survey period. It is crucial, therefore, to conduct a pilot study designed to elucidate which species occur within a given region and during which periods. Having accomplished that step, site selection can begin, stratified according to Type 1, 2, 3 areas. Select and survey as many sites as possible (especially types 1 and 2) within the constraints of funding and personnel, calculating shorebird-days as described above (and in Bart et al. 2002; also see websites listed below for more information on site-selection and other issues related to region-wide, long-term population monitoring).
Selection bias occurs when some part(s) of the study area cannot be surveyed due to limited access or some other constraint, and the proportions of birds that use the surveyed versus unsurveyed areas change during the survey period. For example, the proportion of birds occurring in surveyed areas gradually increases during the survey period from 25% to 75% while decreasing in unsurveyed areas from 75% to 25%. In this case, the data would indicate an increase in the number of birds using the site when actually the number had remained stable. A priori delineation of Type 1, 2, and 3 areas at your study sites will help you determine the proportion of birds you are seeing at any one time in any one type. To delineate areas of differing types, alternative methods (e.g., boats, aircraft) for gaining temporary access to otherwise inaccessible areas could be employed. If the problem is one of limited personnel and/or the time it takes to cover a large study site, consider employing volunteers of other colleagues to help you cover more area during your surveys. If your assistants cannot identify shorebirds, at least have them track the number of birds leaving or entering a given part of your site, and to/from which direction, while you survey another area. This would at least make it possible to determine whether changes in the number of birds you count are probably the result of birds shifting from one area to another or the result of real increases or decreases in the number of birds using the site.
Site-based surveys are useful for describing species composition, habitat use, and phenology, all of which may be very useful for ARM. A significant advantage of site-based, short-term monitoring is the possibility of conducting a census (total count) as opposed to sampling populations. Many specialists in avian population biology recommend that, whenever possible, new monitoring programs should use methods that yield direct or essentially unbiased estimates of population density (e.g., counts when all birds are visible), rather than relying on indirect, or index, methods (Nichols et al. 2000, Bart and Earnst 2002). The rationale for this recommendation is that too many sources of bias exist with index methods for a high level of confidence in the trend estimates that they produce.
Within the context of PRISM, we are not advocating that standardized methods be used across the broad range of habitats encountered. If surveys estimate the average number of shorebirds present during the survey period rather than an index, there is flexibility in the approach and survey methods used in each region and site. For example, depending on the size of the site, accessibility, and vegetation characteristics, either aerial or ground surveys can be used. A site can be completely censused when feasible, or sampled when a census is not feasible. PRISM can also incorporate sites into the Type 1 stratum at any time and for any time period.
Because habitats, conditions, accessibility, and bird dispersion patterns vary considerably, it is not feasible to specify a standard technique that can be used in every situation.
For site-based purposes, the data can be entered on a local PC in a format that makes them most useful to local managers for addressing ARM and related goals. If the data set is large, it is useful to use a relational database (such as Microsoft Access) so that bird survey data and habitat data can be entered in separate files and joined later.
If a given study site is part of a long-term, region-wide
monitoring program, you also need to submit your survey data to ISS, MSS,
or WSS. ISS currently supplies a downloadable survey form on their website
The website also provides information about the ISS including the sites
being surveyed and opportunities for data retrieval.
Because the techniques described herein for site-based monitoring assume that surveys result in a complete census of shorebirds using the study site, data summaries and descriptive statistics can address the many goals of the survey.
There are many efforts underway to monitor shorebirds and their habitats. Specific programs and their URL addresses are listed below. Some provide a general overview of their program, while others also provide details of protocol used, including data forms. We list a few additional sites unrelated to monitoring for your interest.
International Shorebird Surveys (ISS) were organized in 1974 by Manomet Center for Conservation Sciences. The intent is to gather information on shorebirds and the wetlands they use. Among other uses, the data have been used to develop the need for, and identify sites for, the Western Hemisphere Shorebird Reserve Network (WHSRN). The data also contribute to our understanding of migration chronologies and conservation-management needs. The following link has more information: http://www.pwrc.usgs.gov/iss/iss.html.
Maritimes Shorebird Survey program is similar to the ISS program, but is specific to the Canadian Maritime Provinces.
Western Shorebird Survey is similar to the two described above, but is specific to western regions of the United States. It was initiated in 2000 by the US Fish and Wildlife Service and the US Geological Survey. Instructions and web-based data entry are available. Also see instructions on Preparation of Regional Monitoring Plans for Shorebirds (in Microsoft Word format).
Program for Regional and International Shorebird Monitoring (PRISM) (this links to a Microsoft Word document). See page 17 for discussion of sampling issues and means of reducing bias. PRISM is discussed earlier on this page. Procedures for conducting shorebird surveys using PRISM techniques, and examples of the products produced using these techniques, are available on the PRISM website at: http://wss.wr.usgs.gov/data/PreparationofRegionalMonitoringPlans.doc (this links to a Microsoft Word document).
South Atlantic Migratory Bird Initiative. The goals of this program are similar to those listed above, but they are more specific to both shorebirds and waterfowl at National Wildlife Refuges and State Wildlife Management Areas.
Lower Mississippi Valley Joint Venture is similar to ISS, MSS, and the WSS, but it is specific to the Mississippi Alluvial Valley and West Gulf Coastal Plain Bird Conservation Regions as defined by the North American Bird Conservation Initiative.
Western Atlantic Shorebird Association is an international joint venture of federal, state, local and non-profit organizations throughout the Americas. It was formed to promote the integration of shorebird research, monitoring, and education efforts along the Western Atlantic flyway and to support management efforts in that region. They use a web-based infrastructure to incorporate new research and monitoring efforts, and to integrate existing educational programs. Although this site does not deal with monitoring, it may be of interest to you.
Pan American Shorebird Program serves to coordinate color-banding efforts between countries in the western hemisphere. It was created to define a different flag color code for each country in the Americas. Again, although this site does not deal directly with monitoring, it may be of interest to you.
If counts are regularly (or randomly) spaced through the period, and if all birds present in the study area at the time of the survey are counted, then the mean number of shorebird-days is estimated by the sample mean times the duration of the survey period in days. Standard methods can be used to estimate standard errors and confidence intervals for each quantity.
Bart, J. 2002. Preparation of regional monitoring plans for shorebirds. http://wss.wr.usgs.gov/data/PreparationofRegionalMonitoringPlans.doc. Manuscript.
Bart, J. and S. Earnest. 2002. Double-sampling to estimate density and population trends in birds. Auk 119: 36-45.
Brown, S., C. Hickey, B. Harrington, and R. Gill (eds.). 2001. United States Shorebird Conservation Plan. Second Edition. Manomet Center for Conservation Sciences, Manomet, Massachusetts. 70 pp. http://www.manomet.org/USSCP/index.htm.
Nichols, J. D., J. E. Hines, J. R. Sauer, F. W. Fallon, J. E. Fallon, and P. J. Heglund. 2000. A double-observer approach for estimating detection probability and abundance from point counts. Auk 117: 393-408.
Skagen, S. K., P. B. Sharpe, R. G. Waltermire, and M. B. Dillon. 1999. Biogeographical Profiles of Shorebird Migration in Midcontinental North America. Biological Science Report USGS/BRD/BSR 2000-0003. U. S. Government Printing Office, Denver, CO. 167 pp. URL: http://www.fort.usgs.gov/shorebirds.
Stenzel, L. E. and G. W. Page. 1988. Results of the first comprehensive shorebird census of San Francisco and San Pablo bays. Wader Study Group Bulletin 54:43-48.
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