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|Aerial Photograph for Cliff (Ledge) Nesting Colonial Waterbirds|
Northern Fulmar, Northern Gannet, Brandt's Cormorant, Double-crested Cormorant, Great Cormorant, Red-faced Cormorant, Pelagic Cormorant, Herring Gull, Thayer's Gull, Iceland Gull, Glaucous-winged Gull, Black-legged Kittiwake, Red-legged Kittiwake, Common Murre, Thick-billed Murre, Razorbill
Note: Species in bold text are those for which the recommended protocol were developed. However, these survey methods may be applied to all of the species within the respective group.
Step one: Flying the colonies
Small aircraft should be used to photograph colonies using standard techniques; in California, twin engine Partanavia aircraft have been utilized to increase the safety of over-water flights but single-engine Cessna's have been flown as well (Carter et al. 1996). When determining the altitude from which to photograph colonies, keep in mind that a minimum altitude of 500 feet is required by the Federal Office of Aircraft Services (OAS)/USGS-BRD/USFWS flight rules for those federal employees. You must also consider whether there are marine mammals present at colonies. If marine mammals are present, permits must be applied for through the National Oceanic and Atmospheric Administration.
It is ideal to have three persons (in addition to the pilot) in the plane to perform various tasks. This will allow two persons to shoot the photographs while a third records the data associated with each colony and pass flown. Most often, a number of passes over the colony will be required to obtain photographs of the entire colony. The altitude of the aircraft should be between 122 - 274 meters, where possible. Two researchers should shoot photographs using 35 mm cameras with rapid shutter speeds (1/500 or 1/1000 seconds), telephoto lenses (300mm telephoto lenses have been reported in the literature, (Carter et al. 1996)). Cameras should be fitted with autowinders to allow quick enough succession of photographs. In addition to photographs taken as passes are made over the colony, it is important that the entire colony is photographed from the front of the aircraft, using a 50 mm lense (or thereabouts). This will provide you with an overview of the colony which will be important when you begin to piece together individual photographs of individual passes and will allow you to determine whether the entire is covered by the passes.
It is vital to record the year, month, date and breeding phenology (nest courtship/building, egg laying, incubation, hatching/chick-rearing, fledging) for interpretation of the counts and to allow comparisons over time and space.
For each survey and colony, the data recorder records aircraft, pilot, observers, date, time, altitude, photo roll numbers, frame numbers, and general notes in the flight log. When several passes are necessary to obtain complete coverage of a colony, the data recorder will describe each pass separately. For example, during a second pass taken from the south to the north of a colony, 12 exposures are taken, numbering from 12 to 24; the data recorder will note in the flight log, the roll number, pass, and frames used during the pass.
During the flight, as rolls of film are completed and new film is loaded into a camera, the data recorder marks exposed film cartridges with a specific roll number corresponding to notes taken in the flight log. Each roll will be developed using an individual mailer marked with the roll number. Once developed, each slide is again labeled with the colony name, photographer, date, and roll number.
Aircraft can disturb birds, leading to increased nesting failure or colony abandonment. Care should be taken to note agitated behaviors. In some cases, ground observers in radio contact with aircraft personnel might be required during initial surveys. Signs of agitation might include head bobbing and birds being flushed off the nests. If agitated behaviors are noted, increase the altitude of the aircraft and note whether the behavior disappears. If agitation continues to be a problem, surveys of that colony should be discontinued.
Step two: Counting aerial photographs
Once developed, those slides providing the clearest image of individual birds and nests should be chosen for counting. Count areas may be marked using landmarks or colony outlines. Once a full set has been pieced together, the slides should be projected onto a white wall or large pieces of white paper.
Total number of nests and birds within a colony: One or two observers intensively search the projected images for birds and nests. Each bird and nest is marked by a felt tip marker, using different colors and symbols for birds and nests (and, in some cases, "sites" and empty nests) of all species present, including nesting and roosting birds. Where nest material is not visible, nests may be inferred from incubation posture of attending adults. For those species that do not build nests (such as Common Murres), you must count all birds. Often these species nest in close proximity to one another, making it difficult to distinguish between incubation posture and other postures or behaviors. Sometimes it is difficult to distinguish between species in a mixed-species colony. Usually, species will nest within the same region of a colony in "species groups" and birds counted within these regions can be assumed to be a species. However, when species cannot be discerned in mixed colonies, these birds should be counted and identified as unidentified species. Unidentified species are not included in colony totals but can be considered when assessing changes in colonies over time.
Things that could bias your counts:
Surveys should coincide with peak nest numbers, which for most cliff nesters, occurs during the mid-incubation to early nest-rearing stage of the breeding cycle. The timing of counts is best determined by the bird's biology at each individual colony (Rothery et al. 1988). For example, in California, one survey per colony per year in late May or early June has been sufficient to obtain a peak or near peak count of nests of Common Murres, Brandt's Cormorants, and Double-crested Cormorants. Keep in mind that peak or near peak counts actually under-represent the total number of nests over the entire breeding season as they fail to include nest failures prior to the survey and/or egg laying that occurs after counts are conducted, and that species will peak at different times.
There are multiple factors that can be used to distinguish between species. Differences in species behaviors, nesting phenology, nest materials and types, and known historical use of specific nesting areas can be used to delineate between species. For example, cormorant species can be distinguished using throat color, nesting habitats, nest materials and types, breeding phenology, and known historical use of specific nesting areas. In California, Brandts Cormorants build nests from seaweed or other vegetation, and Double-crested Cormorants often use large sticks. This detail may show up on quality photographs. Often breeding phenology can be used within regions, with one species nesting earlier than another.
Advantages: One advantage of using aerial photographs is that counts over a large area can be completed during a short period of time, allowing counts during the same or similar nesting stage. Another advantage is that often, aerial photographs are less disruptive to the colony and result in the adults spending less time off the nest. Finally, aerial photographs can be more economical than direct counts.
Disadvantages: Aerial photographs may not provide as precise information as direct counts. It is difficult to distinguish between species at some sites, nests are hidden by ledges, and, as mentioned above, it is difficult, or in the case of the Common Murre, impossible to distinguish between breeders and nonbreeders.
Variability in detection amongst observers and amongst sites leads to problematical comparisons between data sets. To control for this, detectability should be measured once, for each observer at each site.
To get at detectability: (ask harry to insert the protocol he and mike parker are using)
Once you've used this technique to gather data, decide which approach to use to analyze your data.
Carter, H.R., G.J. McChesney, J.E. Takekawa, L.K. Ochikubo, D.L. Whitworth, T.W. Keeney, W.R. McIver, and C.S. Strong. 1996. Population monitoring of seabirds in California: 1993-1995 aerial photographic surveys of breeding colonies of Common Murres, Brandt's Cormorant, and Double-crested Cormorants. Unpubl. Final report, U.S. Geological Survey, California Science Center, Dixon, California.
Rothery, P., S. Wanless, and M.P. Hrris. 1988. Journal of Animal Ecology: 57:1-19. Analysis of counts from monitoring guillemots in Britain and Ireland.
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