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The Uses of Marking and Recovery Data in Migratory Bird Conservation, Research, and Management

Banding of live birds, which are then released back into the wild and subsequently encountered either through observation, trapping, or recovery of the band when the bird is dead, forms the basis for the estimation of important population parameters. Analysis of these population vital rates contributes to an understanding of the life history and population dynamics of various species. An understanding of these dynamics, in turn, is critical to evaluations of management actions, including the establishment of appropriate exploitation rates for hunting; assessments for actions to improve the status of a species, especially threatened and endangered species; or assessments of the effects of changes of habitats on all bird species. Banding is thus an important tool that researchers and managers employ to further the understanding of bird population ecology and one that can be used to provide direct feedback on various results of the management actions, including manipulation of habitats and harvest rates. Analysis of banding data can also play a major role in monitoring the status of species of concern and threatened or endangered species.

Background and the Bird Banding Laboratory’s Role

The North American Bird Banding Program is directed in the United States by the Bird Banding Laboratory (BBL), Patuxent Wildlife Research Center , U.S. Geological Survey (USGS) and in Canada by the Bird Banding Office (BBO), Canadian Wildlife Service (CWS). The BBL and the BBO have a close cooperative relationship and share responsibilities and data. Responsibility for migratory birds rests at the Federal level as a result of the Migratory Bird Treaty Act of 1918 and its amendments. In order to capture, possess, or mark a migratory bird one must have a permit. In the United States , permitting is a shared responsibility of the U.S. Fish & Wildlife Service (FWS) and the USGS. The FWS administers, among others, incidental take, salvage, scientific collecting permits and the USGS administers banding and marking permits. Hunting of migratory birds is a licensed activity, with administration delegated to the States.

To obtain a banding permit one must have a legitimate reason for banding, either for research reasons or as part of an ongoing monitoring program. Applications are reviewed and the qualifications of the bander ensured prior to issuance of the permit. Handling of birds by its nature carries risks for individual birds. It is the BBL’s responsibility to minimize, to the extent possible, these risks by evaluating carefully the potential costs versus the benefits gained for each banding activity.

The BBL plays a vital research coordination role. Coordination varies from oversight of marking efforts to facilitating communication among researchers. Marking protocols must be coordinated to ensure that data are useful. For example, if a shorebird with a colored auxiliary leg-band is observed during fall migration, the source of the band must be known. Additionally, the BBL must facilitate communication among researchers to ensure that there is no confusion over the source of color markers and that protocols are correct and have been followed. There are many other such coordination roles undertaken by the BBL and they are vital to ensuring that research projects are successful and the resulting data are reliable and useful to the research and management communities.

The database management role that the BBL plays with banding and encounter data is critical. Management decisions based on faulty data can be disastrous. BBL personnel, through an elaborate process of error checks, ensure that data entered into all BBL databases are of the highest quality.

Historically, processing game bird banding and recoveries constituted the bulk of the BBL activities. Banding was widely used, especially by waterfowl researchers and managers, to investigate game bird population dynamics and to provide input for the annual setting of hunting regulations. These activities remain, and in fact have increased as the management community came to understand the need to gain knowledge about individual species. Recently, such investigations have moved management to more fine-grained scales. The most noted changes in BBL activities have been the increase in bandings and encounters associated with non-game birds. In part, this reflects the changing nature of bird conservation and research. Through time, there has been increased interest in non-game birds, including threatened and endangered species, raptors, Neotropical migrants, shorebirds, sea birds and others. Federal (especially the FWS), State, and Provincial agencies have steadily increased their activities with these species as they have addressed new challenges and responded to new management issues. This trend will undoubtedly continue as these agencies continue to embrace their evolving management responsibilities.

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Use of Banding Data

Historically, the first uses of banding data were to study the movement patterns of birds. The location of the bird at the encounter site, coupled with the location of the banding site along with the corresponding dates, describe the location, direction, and timing of movement. Based on these observations, there is also the opportunity to understand the fidelity of birds to areas, including breeding areas, pathways of migration, and wintering areas. These types of data can be used to define population units of birds that share similar behavior, life histories, and space.

For harvested species there is an increased probability bands will be encountered, compared to non-hunted species, and thus the opportunity to better understand movement patterns is increased. An understanding of harvest distribution and harvest derivation is important to the development of hunting regulations. Harvest distribution describes the distribution of birds from a particular banding area while harvest derivation describes the breeding populations that contribute birds to a particular harvest area.

While the increased recoveries of hunted species results in information useful in understanding movement patterns, the limitation of what happens between encounters remains unknown. Modern tools such as telemetry are helping to answer these questions. Satellite transmitters are currently being used to study the migration of larger birds, such as raptors, (e.g., Swainson’s hawks), to South America . With improved technology and miniaturation of equipment, such approaches may soon be available to study the movements of even smaller Neotropical migrants. Radio-transmitters have become small enough to study localized movements of most birds, but because such small transmitters only transmit for short distances and have a short battery life, they are not suitable to investigate long-distance movement. All marking of migratory birds, including use of radio-transmitters, is administered by the BBL. This control is necessary to ensure that marked individuals are handled properly, that national and international coordination occurs, and that proper procedures are followed.

Recovery data can be used to assess harvest pressure. Harvest rate is the proportion of the birds harvested and is calculated by dividing the recovery rate (the portion of the banded sample recovered by hunters and reported to the BBL) by the band-reporting rate. The band-reporting rate is the proportion of recoveries by hunters that are reported to the BBL. The recent change from a mail-based system to one using a toll-free phone for reporting recoveries has more than doubled the band-reporting rate. Band reporting rates are assessed through reward band studies. Currently the FWS, in cooperation with the BBL, is assessing these rates for mallards, black ducks, wood ducks, and various goose populations.

To properly manage hunting of game birds it is important to understand harvest vulnerability. Almost all hunters understand that some species are easier to hunt than others. The same holds true for some age/sex cohorts (groups of birds with similar age and sex) within a species. The relative vulnerability of a cohort is estimated by dividing its recovery rate by that of another cohort. Usually, young are more vulnerable than adults, and males more vulnerable than females. Managers measure the actual harvest of birds using a harvest-survey questionnaire. The age ratio of the harvest (young/adult) often is used as a measure of production. However, the observed age ratio is a function of both production and differences in vulnerability among cohorts. By correcting the harvest age ratio (from the questionnaire) for differential vulnerability (using banding and recovery data), the true age ratio of the population, prior to the hunting season, can be estimated.

The encounters of birds after banding can also be used to estimate survival rates of young and adults. An understanding of survival is vital to an understanding of the population dynamics of a particular species. In addition, the effects of environmental conditions and the effects of management actions on survival can be investigated using banding and encounter data.

Canada and the U.S. have cooperative banding programs that monitor a wide range of species. The preseason waterfowl-banding program is a joint effort of the FWS, CWS, State and Provincial wildlife management agencies, the Flyway Councils, and nongovernmental waterfowl advocacy and research organizations. Annually, ducks are banded throughout Canada and the U.S. breeding areas just prior to hunting seasons. Recoveries during the hunting season provide critical information for the establishment of subsequent hunting regulations. Similar banding efforts occur with selected goose populations. This year, a major banding effort was initiated by many States, through the Flyway Councils and FWS, for mourning doves to gain information needed for more informed management.

Banding has become an ever-increasing monitoring tool to gain an understanding of the population ecology of many non-game species. Recent efforts have emphasized using banding to estimate population vital rates. The Monitoring Avian Productivity and Survivalship (MAPS) stations are extensive capture/recapture efforts to study non-game, primarily the population ecology of passerines. Similarly, banding is used by researchers to study the population dynamics of numerous species, including species of special concern, as well as threatened and endangered species. Many of the bird focus groups, such as the Seabird Group, advocate greater use of banding or marking programs to study or monitor status and trends. This shift in emphasis toward expanded monitoring programs will undoubtedly continue as research and management agencies, both at the Federal and State/Provincial levels, focus more on a holistic approach to conservation and management of all bird species.

The existence of the BBL databases allows large-scale analyses; both spatially and temporally. In some cases these were planned when the data were gathered, for example estimates of waterfowl population vital rates. However in other cases the analyses are opportunistic, in a sense meta analyses. These metadata analyses present research opportunities that would not exist except for the existence of the databases and the important role the BBL plays in encouraging and facilitating such research. In addition, the BBL has been a partner in many research projects, the latest example being an evaluation of the potential aging and sexing errors that may be made during FWS wing-harvest surveys.

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Banding and Management

The annual setting of hunting regulations is the product of managers understanding the population status, dynamics, and the anticipated hunting effects on exploited species. Managers create models of the birth and death processes, including the effects of hunting that operate on the species. In the past, these models tended to be somewhat qualitative, but over the last several decades they have become more quantitative and more explicit, relying on estimates of vital rates derived from band-return information. The quantitative nature of this approach has resulted in greater use and greater demand for monitoring data. The use of explicit models demands estimates of population vital rates; banding and recovery data are a primary source for this information.

Although in some cases the management community has consensus on the conceptual model that explains the population dynamics of a certain species this often is not true. In many cases, there is disagreement about those factors influencing population change. An example would be disagreement on the effects of exploitation on a population. In other words, is hunting a source of mortality that adds to other sources or is hunting mortality compensated for by a decrease in mortality from other sources? Since 1994, the FWS has been using an adaptive management process to guide duck harvest management. Adaptive Harvest Management (AHM) is a formal process where differing hypotheses of mallard population dynamics compete against one another.

The AHM process consists of four basic elements: an objective function, a set of models of mallard population dynamics, a set of regulatory packages, and monitoring data. An optimization ties these four elements together. The long-term objective selected by the Flyway Councils and FWS is to maximize the harvest. This objective is constrained with a desire to meet the population goal of the North American Waterfowl Management Plan. When populations are at or above the North American goal the objective is toward maximizing harvest. When below the goal the harvest is discounted in order to meet the population goal; theoretically at some population level the need to reach the goal will result in a closed season.

Currently the AHM construct for mallards consists of four population models; these differ as to whether harvest is additive or compensatory to other forms of mortality and whether reproduction is strongly or weakly density dependent. There currently are four regulatory packages. These vary from Liberal, Moderate, Restrictive, to Closed. Each package has a predicted harvest-rate distribution. Annually monitoring data are collected, input into the population models, and predictions of next years’ populations are made. A numerical optimization process is utilized that chooses the regulatory package that best meets the overall objectives and the hunting season is set.

The next year the predictions of the four models are compared to the actual data from the monitoring process. These comparisons result in changes in one’s confidence in the models with confidence increasing for those that predict well and confidence decreasing for those do not. AHM is thus an iterative process that hopefully leads to a better understanding of the population ecology of the mallard, to more informed management, and to model improvement. Banding and recovery data are important in the estimation of model parameters and in estimating realized harvest rates, and these data are critical inputs into the annual AHM process.

USGS researchers and FWS managers are currently applying Adaptive Resource Management (ARM) principles to habitat management. The principles are somewhat similar to those described for AHM; in reality AHM is an example of an ARM process. In these efforts FWS managers expect that the ARM process will improve their ability to manage National Wildlife Refuge lands to benefit birds. Some of the monitoring activities associated with this program involve capture, banding/marking and release of birds (all birds and not just waterfowl); thus, the BBL plays a significant role in providing data into the ARM process.

The same conceptual framework that governs harvest management also governs the understanding of all other species as well. For some species, e.g., endangered species, researchers and managers have a good understanding of their population dynamics and have created detailed models that are useful to management for recovery efforts. For other species, data are sparse and understanding is very poor. In these cases, informed management opportunities are few.

The history of bird conservation management has been one of increasing research and monitoring efforts and enhanced understanding of population dynamics. This trend will undoubtedly continue as more is expected of natural resource managers. This means that land management agencies, and agencies with conservation responsibilities, will continue to expand their scope of activities to meet these stewardship responsibilities. Current efforts to expand bird monitoring and management to all birds will continue and thus more informed management lies in the future. Banding and encounter data are, and will continue to be, a critical tool in this effort.

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