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|Coastal Beach Nesting Shorebird Counts|
Author: Susan Haig, USGS Forest and Rangeland Ecosystem Science Center, 3200 SW Jefferson Way, Corvallis , OR 97330, email@example.com, 541-750-7482.
Charadrius alexandrinus, Snowy Plover
Shorebirds nesting on beaches have cryptic plumage that makes them difficult to observe, particularly when they are sitting on nests. Further, most are quite sensitive to the presence of humans and may hide behind a log or squat in the sand so they are further camouflaged from the observer. Thus, they can be difficult to survey.
The only standard protocol for this group is that used for the International Piping Plover Census (Plissner and Haig 2000, Ferland and Haig 2002, Haig et al. In review). One to two observers (and no dogs) simply walk down the center of the beach with binoculars and look for birds either foraging on the shore?s edge or wrackline, or for birds running back up to their nests in the higher beach. Observers are trained not to look for, or walk over to, nests as the disturbance could alert a predator. Rather, they stay mid-beach and record the number of birds observed. Walking slowly and pausing regularly can help as sometimes plovers hold still while the observer walks but run when the observer stops. If an observer is close to a nest, the plover may try to distract it away from the nest with a broken wing display. They are territorial but in the face of a predator (human or otherwise) they will continue to chase the observer quite a ways down the beach, picking up neighbors of the same or different plover species as they go. This can make it difficult to get a good idea of how many birds are present. However, the only other way to avoid this is to set up towers back from the beach and watch from the tower. Since this is hardly practical on a large scale, we are left doing the best we can as we walk down the beach.
One important consideration in plover surveys is to just report the number of birds that are seen. Just because only one bird is seen near a nest does not necessarily mean that there is another bird. There may be another bird further down the beach on incubation recess, but if you count two (when observing one) at the nest site and then a third bird down the beach, counts will be over-estimated.
The field time involved is just what it takes to walk leisurely down the beach, providing observers are familiar with identifying the species to be surveyed. Most beach nesting shorebirds are quite simple to differentiate from each other.
Office time is fairly minimal because all that is needed is a final count of how many birds were observed and where they were observed. Because there is no standard sampling protocol for this method other than going for a walk on the beach, there are no sophisticated statistics associated with the data analyses. Data are just a summary of the number of adults and chicks observed. However, some time will need to be allocated for entering data into a database and downloading GPS locations if they are collected in the field.
Things that could bias your counts
Observer skill is most important in being able to follow cryptic birds that fly along or run along in front of them so as to avoid double-counting. It is important that observers are not only are familiar with species identity but that they are keen on searching for quick movements of very cryptic birds. Adults can be a challenge to observe and chicks and nests are even more difficult to spot. As mentioned above, species identification of North American beach nesting shorebirds is generally simple.
As mentioned above, observers can have huge effects on census results. Plovers on beaches are quite wary, hence observers should quietly carry out their work Unless the same observer covers the same areas survey after survey, there is no systematic way of dealing with these effects before or after censusing, thus care should be taken to be quiet and observant.
In general, one visit is all that people carry out if multiple sites are being censused. Multiple visits to a site can be helpful but only to a point. If adults or chicks sense return visits of someone interested in them, they may remain hidden longer and become more difficult to count. Similarly, if observers are looking for nests, multiple visits will help in that if nests were not discovered in an initial visit because all eggs were not laid and complete incubation had not commenced, it may be easier to spot birds on subsequent visits. However, too many visits will make the birds wary and they will hunker down making it difficult to find the nests.
There is not a great deal of difference among nesting habitats (within species) for beach nesting plovers in similar regions. Thus, sites can be censused in a similar way for each species. However, intra-specific differences do occur between inland and coastal habitats of Piping and Snowy Plovers. For example, in the Midwest they can be found on river sandbars or small alkali wetlands while they would only be found on long beaches in coastal areas. It may be simpler to observed them in the more restricted habitat than the more vast habitat. If multiple species are being censused, Killdeer nests will be found higher in the grass than other plovers, hence observers may have to walk close to the grass edge to find them.
Weather can have a dramatic effect on results. Thus, it is important not to census when it is raining and windy. In bad weather, birds hunker down behind logs and rocks and are exceptionally difficult to observe. Tides can also cause results to vary in that it may be harder to find all the birds at low tide when vast expanses of habitat are exposed. Thus, each location and species should be considered with respect to tidal influences.
Census times should be adjusted to be carried out once all 4 eggs have been laid in nests and birds are in full-time incubation. Waiting an additional week after the 4th egg is laid further guards against desertion by the pair. The worst time is either at the beginning of the breeding season when there are either no nests (if nests are being counted) and birds are flying all over and difficult to pin to territories. After chicks hatch is a difficult time as well as often one parent will desert the brood and either move away from the nest site but remain in the vicinity or they will migrate. These times will have to be adjusted given locations of censuses and may vary geographically, posing some difficulties in carrying out simultaneous large scale censusing of a species.
Censuses should be carried out in early (i.e., within the first 3 hours of daylight) morning when birds are just getting off nests to forage. Usually, the light is good and the wind is calm. The worst time is mid-day when winds are often at their highest and it is hot. Birds tend not to move much in the heat particularly if they have young chicks which may suffer as a result of sun exposure.
The advantage of nest/bird censuses on beaches is that the procedure is straightforward and simple. The disadvantage is that the birds may be wary on open beaches leading to biases in number of birds observed. There is no way to correct these biases.
Data are analyzed in a simple fashion with just summary statistics. Extrapolating results from one area to another (on the same site or another) usually results in erroneous estimates as nesting is not uniformly distributed in habitats. Thus, it is not recommended.
These protocols have most frequently been used by the international conservation efforts for Piping Plovers and during the International Piping Plover Breeding censuses that take place every 5 years. They have also been used extensively by Snowy Plover biologists on the west coast.
See Existing protocols and programs using this technique and Literature cited sections.
Haig, S.M., C.L. Ferland, D. Amirault, F. Cuthbert, J. Dingledine, P. Goossen, A. Hecht, and N. McPhillips. The importance of complete species censuses and evidence for regional declines in Piping Plovers. Journal of Wildlife Management (in review).
Haig, S.M., and J.H. Plissner. 1993. Distribution and abundance of Piping Plovers: results and implications of the 1991 International Breeding and Winter Census. Condor 95: 145-156.
Page, G.W., L.E. Stenzel, W.D. Shuford, and C.R. Bruce. 1991. Distribution and abundance of Snowy Plovers on its western North American breeding ground. Journal of Field Ornithology 62: 245-255.
Plissner, J.H., and S.M. Haig. 2000. Status of a broadly-distributed endangered species: results and implications of the second international Piping Plover census. Canadian Journal of Zoology 78:1-12.
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