Breeding populations of seabirds in California, 1989-1991. Volume I - population estimates Item Type monograph Authors Carter, Harry R.; McChesney, Gerard J.; Jaques, Deborah L.; Strong, Craig S.; Parker, Michael W.; Takekawa, Jean E.; Jory, Deborah L.; Whitworth, Darrell L. Publisher U.S. Fish and Wildlife Service, Northern Prairie Wildlife Research Center Download date 05/10/2021 11:10:39 Link to Item http://hdl.handle.net/1834/27469 BOW TO USE MAPS AND TABLES A few minutes taken to carefully read this section will facilitate the use of these maps and tables in this report. Colony Numberinq Systems Varoujean (1979) and Sowls et al. (1980) identified the location of each breeding colony known in California on 1 of 11 u. s. Geological survey (USGS) maps which cover the entire California coast. An index to these maps has been presented in Figure 53. Colonies were numbered under a u.s. Fish and Wildlife Service (USFWS) colony numberinq system covering the entire united States. The first three digits of the six-digit USFWS catalog number for each colony was the map number, whereas the last three digits were colony identifiers (each specific for a nesting colony area within that map) • However, because seabird colonies were discovered over a period of time, USFWS colony numbers within each of the maps were not sequential along the coast. Many new colonies were identified by Sowls et al. (1980) and 1989-1991 (This study), after colony numbers were assigned initially by Varoujean (1979). As did Sowls et al. (1980), we retained these original USFWS colony numbers and added new colony numbers as necessary. In this way, survey data for specific colonies over time always was attributed to the same colony site. While it was critical to have this standardized USFWS colony numbering system and for it not to change over time, it has become more difficult and confusing to access data from the Catalog as new colonies were discovered. Colony numbers increasingly have become out of numerical and north-to-south order along the coast. These data have been recently computerized, alleviating this problem to some extent for those who have access to this, previous, and future data sets. However, many users of this report will not have this flexibility. Thus, we developed the California ( CA) colony numbering system that: 1) ordered all known and historical colonies in 1989-1991 from north to south; 2) allowed for additions of new colonies in the future without jumbling the numerical or north-to-south order of colony numbers over a large section of coast; and 3) separated colonies into political units (i.e. county) as well as more natural geographic units (e.g. Channel Islands). We recognized that the CA system must be not only more useful than the USFWS system but also must be compatible with the USFWS system. Thus, we built the CA system as a subdivision of the USFWS system. We also recognized that the CA system will only apply to California and will not be adopted at the national level. For this reason, we cross referenced USFWS and CA colony numbers in the tables and appendices such that the user can choose to use either system. In Figure 54, we presented the 29 CA system map blocks (plus separated blocks for the Farallon Islands (FAI); San Francisco Bay I-276 (SFB); Channel Islands National Park Area; and the Southern Channel Islands. When juxtaposed with the 11 larger map blocks of the USFWS system (Figure 53), one will notice the relationship to the CA blocks and latitude. The 29 blocks were 20' latitude subdivisions of the coast. Each block's number referred to it's latitude and thus has inherent· value in describing a colony's location (e.g. 384 = 38°40' to 39°00'N). However, since several counties may occur within this latitude block, we have prefaced it with a two-letter coastal county code (Table 48). Thus, all colonies were first assigned a county code. This designation was especially important for the four separated blocks where the latitude block number was omitted. In the Channel Islands, we replaced the latitude identifier with abbreviations for each island: san Miguel Island (SMI), Santa Rosa Island (SRI), Santa cruz Island (SZI), Anacapa Island (ANI), Santa Barbara Island (SBI), San Nicolas Island (SNI), santa catalina Island (CAI) and San Clemente Island (CLI). For the Channel Islands, colonies were presented in the above island order and colonies were numbered in a clockwise direction starting at the northwest corner of each island. In San Francisco Bay, we prefaced colony numbers with SFB to prevent confusion with colonies in some of the same counties (Sonoma, Marin, San Francisco, and San Mateo) on the outer coast. Similar ·to the Channel Islands, colonies in San Francisco Bay were not presented in north to south order. Instead, colonies were ordered in a clockwise direction starting at the north end of the Golden Gate Bridge. The two-digit suffix was the colony identifier (each specific for a colony area within the county and 20' latitude block or other block). Since these blocks were much smaller than the USFWS system maps, we felt that it was necessary to assign only two digits since fewer than one hundred colonies could occur within a county or island in a CA system map block. To demonstrate differences between the USFWS and CA colony numbering systems, we considered the following example: USFWS system 325-006 Castle Rock CA systein DN-414-06 Castle Rock If unfamiliar with the USFWS system, one would know nothing about where castle Rock was located and would be confused between castle Rocks in Del Norte, Monterey, Santa Barbara and Los Angeles counties. Even once familiar with the USFWS system, we still would only know that this colony occurred somewhere between 40° and 42° N latitude. Using the CA system, we know that this colony was located in Del Norte (DN) county, between 41° 40' and 42° OO' N latitude, was the sixth colony from the north end of the county coast and undoubtedly was Castle Rock National Wildlife Refuge. I-277 Tables: Estimates of numbers of breedinq birds by species and colony For each colony, we have presented non-rounded estimates of the number of breeding birds (not breeding pairs) for each species under the "TOTAL BIRDS" column-. In a few cases, "X" or "P" indicated that birds were breeding or probably/possibly breeding but an estimate of the number of breeding birds was not available. Actual raw numbers obtained during censuses were presented under 1 11 11 the "NEST ', 11 BIRD , and 11 SITE columns (see methods for how raw numbers were treated to obtain breeding bird estimates). Raw numbers will be more valuable for some users' purposes. The letters 11 ND 11 indicated that no data were collected or a complete count was not available. Numbers of nests included: nests that were empty, attended by an adult in incubating posture, attended by adult(s) standing in or beside a nest, or eggs/chicks were present. Sometimes, the numbers of nests could not be or were only partially determined, usually due to poor observing conditions, large chicks creching or leaving nests or ·nests were not visible (e.g. Common Murres). Numbers of birds included: birds in nesting areas only (i.e. Double-crested and B~andt's Cormorants, Western Gull, and Common Murre); all birds combined from nesting areas, on the ocean near land, and flying over water/land (i.e. Black Oystercatcher, Pigeon Guillemot, Rhinoceros Auklet, and Tufted Puffin); birds in the nesting area plus roosting birds at active subcolony sites only (i.e. Pelagic Cormorant); or birds mist-netted, heard, or otherwise found at colonies (.i.e. storm-petrels) . Sometimes, numbers of birds could not be or were only partially determined, usually due to poor observing conditions, large chicks mixing with adults, flushing of adults, etc. Numbers of sites included: possible nest sites where birds were recorded in a probable/possible nest location but nests were not observed (i.e. Black oystercatcher, Western Gull); potential nest sites attended by birds but nests were not present or when these were not distinguished from active nests (i.e. Pelagic Cormorant); burrow/crevice entrances counted on nesting islands (i.e. Pigeon Guillemot, Xantus' Murrelet, Cassin's Auklet, Rhinoceros Auklet, and Tufted Puffin); or (usually) burrow/crevice entrances attended by birds that were counted from boats (i.e. Pigeon Guillemot, Tufted Puffin). All CENSUS DATES were in 1989-1991, except where historical or other data were substituted due to incomplete coverage. CENSUS METHODS were coded as in Table 49. When colonies and/or subcolonies were censused more than once, we selected the census with the highest number of nests, birds, andfor sites for estimating numbers of breeding birds. When more than one census date and/or method was indicated for a species in tables, numbers of nests, birds, and sites have been summed from different subcolonies or different parts of the same subcolony. ' To assist comparisons between 1975-1980 and 1989-1991 surveys, we asterisked newly-discovered colony numbers, newly-discovered I-278 nesting species at previously-known colonies and newly-rediscovered historical information. In addition, when a species was not found nestinq at a colony in 1989-1991 where it had nested previously, we appended information on the most recent nesting of historically­ nesting species. We have not included data on rocks, islands, or mainland points where either only roosting or no birds were observed in 1989-1991 or 1979-1980 surveys. In 1989-1991, we combed almost the entire coast so that any rock that has not been listed as a colony can be considered to have been checked at least once dur.inq the main part of the breeding season.