Academic journal article Environmental Law

Animal Migration as a Moving Target for Conservation: Intra-Species Variation and Responses to Environmental Change, as Illustrated in a Sometimes Migratory Songbird

Academic journal article Environmental Law

Animal Migration as a Moving Target for Conservation: Intra-Species Variation and Responses to Environmental Change, as Illustrated in a Sometimes Migratory Songbird

Article excerpt

I.  Introduction
II. "Sometimes Migratory Songbird": The Dark-Eyed Junco
    A. Diversity Within the Genus Junco
    B. The Junco as a Model in Science
    C. Conservation Issues and Status
    D. Migration in the Junco
III. Geographic and Subspecific Variation in Migration
    A. Migratory Diversity Among Junco Groups
    B. The Generality of Intra-Species Variation in Migrations
    C. Geographic Variation in Migrations: Implications for Conservation
IV. Intra-Population Variation: Partial and Differential Migration
    A. Partial Migration
    B. Differential Migration
    C. The Junco, a Differential Migrant
    D. Differential Migrations: ImpUcations for Conservation
V. Migrations as Dynamic Phenomena: Responses to Environmental Change
    A. Shifts in Junco Winter Distribution and Sex Ratio Associated with
       Climatic Warming
    B. Rapid Loss of Junco Migration Following Establishment in a Novel
       Urban Environment
    C. Migration as Dynamic in Response to Changing Environments:
       Implications for Conservation
VI. Conclusion.

I. INTRODUCTION

Animal migrations are dynamic phenomena that vary over space and time, even among closely related species, populations, and individuals. For example, in many animals there is substantial geographic variation in the migratory tendencies of different subspecies, races, or populations-birds that breed in the north may migrate long distances south to spend the winter, whereas members of the same species that breed at lower latitudes may be entirely sedentary (i.e., non-migratory). (1) Further, even within a discrete population, there can be systematic differences in the distance, routes, endpoints, or seasonal timing of migrations among male versus female or younger versus older individuals. (2) Such variation in migratory behaviors can emerge rapidly over "evolutionary time scales" (e.g., thousands of years)-including over contemporary times (e.g., years or decades) in response to human activities such as habitat alteration and climate change. (3) Therefore, effective conservation agendas for animal migrations must consider the implications of both spatial and temporal variation in migratory behavior, even within a single "migratory species" or a single local population.

Our primary goal in this paper is to introduce the following three biological topics to nonspecialists, and to discuss their potential implications for legal, policy, management, and research agendas related to the conservation of migrations: 1) geographic variation in migratory behavior within-species (i.e., inter-population variation in migration), 2) variation in migration of different individuals within a single population (i.e., intra-population variation in migratory behavior among individuals), and 3) the sensitivity of migratory behavior to environmental change-with dramatic changes observed even over relatively short time scales.

To illustrate these topics, we use a common "backyard" North American songbird species, the Dark-eyed Junco (Junco hyemalis). (4) We chose the "sometimes migratory" junco, not because this species's migration is of immediate conservation concern (it is not), (5) but because past scientific research has revealed the complexity of its migration, (6) allowing it to serve as a model to convey why intra-species variation in migration-and the sensitivity of migratory behaviors to environmental change-provide important challenges and opportunities for policy efforts to protect migrations. Principles derived from the junco almost certainly apply to many other migratory species, including those of immediate conservation concern, and we provide selected examples. (7) However, for most species, intra-specific variation in migration or the potential impacts of changing environments on migration have not been well characterized. Even for the junco, which has received much research attention from biologists studying migration, there remain many unanswered questions about migratory variation within and among junco subspecies and populations. …

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