MONITORING THE ABUNDANCE OF BIRD POPULATIONS

Large-scale, long-term programs to monitor bird abundance have provided the foundation for many of our most successful programs to study and conserve bird populations (Brown et al. 2001, Williams et al. 2002, Kushlan et al. 2002, Rich et al. 2004, U.S. Fish and Wildlife Service 2004). Those programs help identify species at risk and limiting factors, suggest and help evaluate management approaches, and document recovery at the regional and rangewide scale. It is difficult to think of a major wildlife issue for which monitoring has not provided essential information. Yet despite the critical role of bird monitoring programs, many of them are poorly designed and coordinated, and many improvements could be made at relatively low cost. In a welcome addition to the bird-monitoring literature, Conway and Gibbs (2005) describe improved methods for surveying secretive marsh birds. Their study is notable because it is based on >16,000 point counts contributed, at the authors' request, by 15 cooperators working on 12 species in 10 states. Only by recruiting collaborators (they wrote to more than 100 authors) could Conway and Gibbs have compiled such a large and spatially extensive database on that relatively unknown group of birds. Their specific question was whether secretive marsh birds are best monitored by broadcasting calls, listening passively, or doing both. Most of their collaborators used both methods, so Conway and Gibbs (2005) used differences in numbers recorded during passive and active periods, thereby excluding extraneous sources of variation such as site, observer, and weather. They also adjusted results to enable comparison of numbers that would have been recorded with periods of equal duration. They compared number recorded per period, the coefficient of variation (CV) of that number (the appropriate measure for examining precision), and the proportion of sites at which each species was recorded. Conway and Gibbs (2005) found that broadcasting calls and songs increased the mean number of responses and the proportion of sites with a response and decreased the CVs, albeit only slightly. They point out that broadcasting some species' calls may reduce the frequency of calling by other species and, therefore, recommend that surveyors employ both a passive period and a period during which calls are broadcast. They conclude by recommending that the removal (Farnsworth et al. 2002) or double-observer (Nichols et al. 2000) methods be used, but they note, appropriately, that those methods estimate a ”component of detectability,” not overall detectability. Their study thus provides a solid foundation for completing the continental monitoring program for secretive marsh birds, a task that the waterbirds initiative has undertaken (Ribic et al. 1999) and that will probably be complete in less than a year. Conway and Gibbs's (2005) study is part of a large effort to improve monitoring programs for waterbirds, shorebirds, and landbirds, particularly programs that monitor abundance at a large spatial scale. The effort is being carried out by several dozen managers and researchers working at the state, regional, and continental scales and includes both new methods and new programs. On the basis of progress during the past few years, we can now envision an interlocking series of programs to monitor birds, using state-of-the-art techniques, which will provide a far better foundation for studying and conserving bird populations than we have had in the past. Here I describe recent progress and the vision for bird monitoring that many of us share. A review is being conducted by the Partners in Flight (PIF) Monitoring Working Group, building on earlier work by Moser (2000), of existing programs whose goal is to collect longterm data on abundance of nongame birds. Information on goals and methods, sponsors, duration, and geographic scope of the programs is being collected. Descriptions are being posted on a North American Bird Monitoring Projects Database website (see Acknowledgments). Most programs of this sort are probably conducted by states and provinces, and most of them have not yet provided descriptions of their programs. Nonetheless, descriptions have already been compiled for 251 programs in Canada and the United States. Extrapolating from that list and our knowledge of other programs not yet in the database, we estimate that the number of programs for landbirds in the breeding season, the number of migration monitoring stations, and the number of surveys of aquatic areas (e.g. on National Wildlife Refuges) almost certainly each exceed 500, and that several hundred surveys of colonies are conducted on a regular, though often not annual, basis. The number of independent programs conducted to gather long-term data on bird abundance in Canada and the United States may thus be as high as 2,000, and almost certainly exceeds 1,000. That large number of programs is a concern, for several reasons. Only a small fraction of the data collected is deposited in long-term databases. C. J. Ralph (pers. comm.) estimates that more than 1 million point counts are collected annually but that <10% of those data are stored in permanent repositories. Many of the programs do not last more than 10 years, and Ralph suggests that the half-life for ”orphaned” data sets is only 5–8 years, which indicates how quickly the data collected in temporary programs are lost when not archived. But even if the data are archived, their use in estimating long-term trends is questionable. For example, few programs use well-defined sampling plans to select survey locations, so extrapolating to larger regions using their data is difficult. Thus, because most of the data collected are lost, and because of questions about methods, most of the programs contribute little to estimating continental trends. Certainly they may achieve other goals, but they would be much more useful if they were part of a comprehensive strategy involving clear goals, well-defined sampling plans, accepted counting methods, permanent storage of data, and regular reports. Partners In Flight was founded in 1990 on the basis of reports that Neotropical migrants were declining (National Fish and Wildlife Foundation 1990). Their ”PIF North American Landbird Conservation Plan,” including recommendations on monitoring, was published in 2004 (Rich et al. 2004). Canada and the United States published separate shorebird conservation plans (Brown et al. 2001; Donaldson et al. 2001), and a single group was then formed to work on shorebird monitoring programs. The remaining nongame species are covered by the waterbird initiative. Their ”Waterbird Conservation for the Americas” (Kushlan et al. 2002) covers both North America and South America and includes monitoring goals. A separate report (Steinkamp et al. 2000) provides detailed advice on methods for surveying selected waterbirds. The need for better coordination among bird surveys has been recognized in the conservation plans produced by the bird initiatives, and much progress has been made in the past five years. The greatest emphasis has been placed on the longterm, large-scale, multispecies surveys to monitor abundance. The shorebird initiative started the Program for Regional and International Shorebird Monitoring (PRISM), a cooperative effort between Canada and the United States (Skagen et al. 2004). Having adopted an accuracy target for trend estimation, PRISM is organizing surveys on the breeding, migration, and wintering grounds to achieve that target. The PRISM collaborators have designed a large project to estimate population sizes of shorebirds in the Arctic. It uses double sampling and habitat-based models (Bart and Earnst 2002), and has been tested widely across the Arctic. Significant efforts to develop shorebird surveys in the boreal region are beginning and will continue for at least the next two years. Less work has been completed on temperate-breeding shorebird species, but the PRISM accuracy target appears to be met for Piping Plovers (Charadrius melodus) and American Woodcock (Scolopax minor) and may be met for five other species that are frequently recorded on the Breeding Bird Survey (BBS), though more work is needed to assess potential bias. In 2004, a two-year study of Long-billed Curlews was initiated (Numenius americanus; see Acknowledgments). The results will achieve the PRISM trend-monitoring target and provide information on habitat relationships and conservation priorities for that species. A comprehensive plan is needed for monitoring eight other temperate-nesting species. Migrating shorebirds have been monitored in North America since the mid-1970s by the International Shorebird Survey (Brown et al. 2001) and the Maritimes Shorebird Survey (Morrison et al. 1994, 2001). Although data from those programs have proved useful in estimating trends (Howe et al. 1989; Morrison et al. 1994, 2001), neither program was initiated as a long-term monitoring program and neither employs a well-defined sampling frame or documented survey methods. Investigators in the PRISM effort have addressed those issues by developing procedures for identifying important sites and regions for migrant shorebirds and detailed procedures for describing sites and how to survey them (Skagen et al. 2004). Less work has been carried out on shorebird wintering grounds, but extensive aerial surveys were conducted in South America during the mid-1980s by Morrison and Ross (1989), with additional work in Panama in the early 1990s (Morrison et al. 1998). Several surveys for single species have been conducted, including a recent one for American Oystercatchers (Haematopus palliatus), undertaken as part of PRISM by Brown et al. (2005). Several major programs monitor landbirds; chief among them is the BBS (Sauer et al. 2001). A great deal of work has been done in evaluating the BBS (O'Connor et al. 2000). Many of the recommendations have been implemented, though additional resources are needed to implement some of the most important ones. Partners In Flight has adopted the accuracy target proposed by PRISM. Rich et al. (2004) discuss how well the target is being achieved, and a more detailed analysis has been conducted for Canada (E. H. Dunn unpubl. data). Recommendations have also been made for a Canada-United States program of breeding-season surveys, and the number of BBS, or other similar, survey routes needed in each province and state to implement the program has been calculated (Bart et al. 2004). Some states (e.g. Nevada, Idaho, New Jersey) are implementing those recommendations. A network of 22 migration monitoring stations for landbirds was created in Canada during the past decade. A separate network of raptor migration stations has also been created (Raptor Population Index; see Acknowledgments), and a comprehensive migration monitoring program for other landbirds is being developed (C. J. Ralph pers. comm.) A detailed summary of continental-scale monitoring needs and priorities for landbirds has been prepared by the PIF Science Committee. Less work at the continental scale has been done by the waterbirds initiative, which, to has efforts more at the regional colonies are well in many regions of North surveys of and colonies are made in many and a few regional surveys are made for other species (e.g. has been done developing rangewide or continental programs to regional information. a continental program is being developed for secretive marsh birds, and programs for other will probably be during the next several years. and the Bird carried out work during the 1990s on to survey birds in a Their of survey routes of and of work on bird (e.g. surveys in early surveys of by the in the to monitor aquatic species have been carried out at the in and in among other monitoring programs are conducted by many for example, the U.S. Service separate regional C. pers. Conservation the Bird and the Bird The work of and and 2002) is a particularly of longterm and and results to the past five years, the nongame initiatives, particularly in the United States the of have on a Bird for comprehensive surveys (Bart and Ralph 2004). Bird Monitoring plans have been completed for and are in New and and are in several other states. The and the of have also to plans, and the North American Bird Conservation a of state, and bird conservation is to of work is being done annually in Canada and the United States to survey birds. It in that more than effort is being on monitoring birds, and that some of those resources could be to work such as identifying of which areas have for or and or evaluating management programs. But as of monitoring is and many improvements in the are some of which will new particularly to improve coordination so that data are not lost and to in A comprehensive is thus needed of programs to monitor bird populations in Canada and the United States. I describe for the of those programs improved coordination and of new methods. at the scale of the management issues being For example, efforts to identify species at risk be at the rangewide which for multispecies programs the continental scale. independent programs are carried out at a it is difficult to collect and managers do not the rangewide needed to whether species are at Thus, a in one state or region may declining in that but may also a by The a need for work the state to conserve the species, the probably would coordination at far of the even that coordination is and is only when exceed is being and to a more appropriate of particularly in the five states are comprehensive wildlife conservation that will conservation by their The U.S. Fish and Wildlife of will review and the as part of their for to states. has published for of the Monitoring is one of and is to a to monitor and the of trends of wildlife and of Fish and Wildlife Information 2004). The which are to be completed by 1 provide an to improve coordination of monitoring work state The also provide the states a for to continental programs. the bird work the of to needed continental programs. the state efforts will be and will not to estimates of trends and other long-term trends in bird abundance are in many programs. if those programs are most species will be monitored by more than one trend estimates is the trend estimates are both rangewide in then the overall estimate is the of the with estimates to the estimates are from of the (e.g. the boreal region and of the then the two areas be as and an overall estimate can be using for the are to be then estimates of the more of the of be the it may be useful to data at the of the (e.g. BBS than at the of the is also using and A separate trend estimate is made at each site, and then the estimates are using to the with which estimates can be it is that so little effort has been in regional programs, to use of programs. regional programs have been designed to use data from the BBS as well as their data the Bird by the Bird is an waterbird surveys are designed of aerial surveys that may at the and aerial surveys of the region are carried out as than coordinated, Program managers that plans for data sets need to be made in the the of the most difficult the bird monitoring is how to that that the data collected are in long-term data repositories. progress has been made during the past with data particularly at the U.S. Survey Wildlife but many or at least to their data, and that has been a to comprehensive databases. a group of by at the of has developed a new based on work in the which to the need for both and comprehensive The for analysis (e.g. estimating trend in bird on a of such as of the (e.g. number of the sampling and numbers of birds recorded by species and least one that will and data from the be so that have a to which they can that to their data do but they on the which, when their database and the of Those so that can for example, from a state, period, and of least one analysis program is also prepared and posted on a can contribute for existing programs or comprehensive analysis programs. A the by calling one of the analysis programs, from and The program then out across the to the data the data the it one or more comprehensive and it to the analysis by the are carried out and including the data, are to the information on this is (see Acknowledgments). That has several can contribute their data to a that to of their data do and can employ information and database they also information is so that information is are a comprehensive and of knowledge for the a vision of how bird-monitoring data can be in a that the of and of the is needed by the bird and by the major in bird a involving to data be an to the and for Many to out bird-monitoring many that could be are the of Bird Conservation and the for Conservation in and questions are about the use of information collected by The is that monitoring program is and is so the information collected in program to our of bird reports by can provide useful information. For example, a report in Science by on both of North America for identify of large in Breeding Bird have increased our knowledge of bird and many programs now counts that of abundance and the of those Many to improve programs, and much work is being done in that areas emphasis are of and for that is between which but need and that whose can be used for the needed and to and for it from the of will states to in the monitoring programs and could be in for those programs. A next in coordination among bird-monitoring programs is to develop a comprehensive program that the programs. not mean that surveyors species on a but that be used for improved a single of existing goals (e.g. accuracy and published some goals between about surveys on which additional species be procedures for data and efforts and The PRISM surveys the that may from between Those surveys are carried out in some of the of North have conducted the surveys only on species were also recorded as but little use was made of the with those surveys have met with from the other and developed procedures for landbirds and waterbirds. a information is being provided on those which the and waterbird would not have been to collect on their because of high effort is to a North American Bird Monitoring that will a comprehensive vision for bird monitoring in North America (Bart and Ralph 2004). It is based on work by the Working of the PIF Science and work on nongame birds in several states. The will landbirds, shorebirds, and some waterbirds and will be to programs in Canada and the United States. It will describe monitoring goals and for them with at the regional, and procedures for data management and will be as well as for monitoring programs and survey methods. Most bird-monitoring programs do not use habitat in survey (e.g. BBS, aerial or do not use a well-defined sampling plan to select sites (e.g. or use neither (e.g. migration monitoring Bird habitat in that little sampling For example, in many of the and areas are not well by the BBS, even though each habitat has species of using a well-defined sampling plan that to large areas is because sampling is not based on habitat plans, is difficult and has been though in PRISM are a The major to be and information about and other useful in (e.g. detailed information on are much small to be used as and or sampling so that their survey in and using habitat information to counts across the region in a that the sampling Most of those issues have been addressed in recent PRISM from the but much work to the of the survey of birds needed to to estimates of to be difficult and 2002, and work has been done in the past on methods for estimating the but we are far from Less has been to how the be but that is because the is often not yet it the we are to many managers and that they their results may be (e.g. in are thus needed for and bird survey methods. The bird are probably an appropriate group to develop such methods that is and in that of provides a basis for accuracy In bird surveys, as other than sampling is often use of results to about populations an about bias. For example, an on between two populations be to differences in of On the other for is difficult and because the data provide much basis for estimates of bias. the estimates be based on other including the population and population of are and estimates of are then is small may be and in most surveys, the population and population of are not In such detailed of potential is needed as part of the That issue more by and of the of such would be that some of their resources from and potential will often to increased work on new is being carried out in several the methods for monitoring bird migration have been developed during the past two particularly by and and are now beginning to implement those methods in programs. is on of species by their calls pers. monitoring by and by calls will of migration and of in those and will provide an independent to trends in abundance. at stations or on have been used to for species during the breeding pers. are being used in Canada to survey areas et al. 2002), and new approaches, which will and are being developed in the United States pers. Those methods, if will the of estimating number of birds at a of survey stations, because the number of birds in a can be as the number of the Those will thus help two how to survey areas and how to estimate based on calls, and will have their sources of potential but in many the will be independent of the in methods that are based on will be when two or methods trend progress is being made in developing continental monitoring programs for birds, and Many species are well by more than one of those programs. For example, in the many landbirds will be on their breeding grounds in the boreal or at migration stations, and on their wintering In those programs, and particularly in how much effort to in each we need estimates of the overall to trends using sources of The of how resources will be among programs, of accuracy of potential will and the overall to trends will The needed for such an is not difficult to but estimates of sizes and trend are needed for each species. A for developing the estimates is also needed that will in a clear of bird-monitoring the estimates and proposed comprehensive can managers to such a plan only if that of is Here the bird are probably the group to out the I have recent and in programs to monitor the abundance of I will by two on which progress is also are needed to develop management and conservation programs and to evaluate the of those and programs when and 1998). The Monitoring and program et al. 2001, and in and now with stations is the only program in North America information on nongame birds. Regional and estimates from are (see Acknowledgments). Bird Canada has to collect information on and the of plans to Program pers. Those programs, and are because them managers would be to with habitat an that is often and 1998). A for increased from the bird-monitoring is bird-monitoring programs with monitoring programs. Although most bird monitoring will continue to be conducted as an independent also for working with collect information. of PRISM in Canada to their surveys by working with in of monitoring with monitoring programs, and with monitoring, are two of the in which bird monitoring will develop during the next five to years. Many of the surveys are made by the efforts of of and to C. J. H. C. and for on the of which was by the and Science The North American Bird Monitoring Projects Database is at For information on the Long-billed see For information on the Population see Information on the is at Regional and estimates from are the National Information Bird Conservation

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