The Changing Seasons Expansions

Pring is a season of change for billions of birds, a time of passage that brims with the sense of urgency to breed, a time rife with increased hormonal activity.This is especially evident among the many species ot long-distance migrants that make their way from points south of the equator to the northern reaches of the western hemisphere.But spring is also a season of unease, as the multitude of pitfalls confronting these migrants become apparent: persistent droughts, violent weather systems, the further spread of West Nile virus, and the gauntlet of anthropogenic obstacles--factory smokestacks, glass-plated skyscrapers, enormous antennas--that proliferate across the continent.In this column, we offer our thoughts on some of the more noticeable patterns we discerned in the spring 2004 regional reports.Many noteworth)' events and observations are digested in Special Attention boxes, which are recommended reading.We welcome the new Northern Canada region to these pages•its presence fills a huge void in the journal's coverage--and we are especially eager to read in coming years about high-latitude species whose ranges are contracting rather than expanding: most of the expanding species considered in this column nest between the U.S.-Mexico and the U.S.-Canada borders, and it is virtually certain that global climate change, while a boon for some species, will be a bane for many others.Our increasing understanding of the changes in American Arctic habitats will hopefully be measurable against reports of birds in this journal, counterbalancing to some degree our bias toward reports from more densely population regions.WEATHER Weather and climate, perhaps more than any other factors, are responsible for the changing patterns we observe in bird distribution.The continental climate in spring 2004 was in most respects a continuation of long-term patterns, the most significant of which was clearly the continued drought in the West.Dry conditions were especially acute in the central Rocky Mountains, the western Great Plains, and the Great Basin: Wyoming had its thirteenth driest and Colorado its twenty-seventh driest spring in more than a century.In Arizona, declines in hummingbirds were attributed to the effects of long-term drought.On the plus side, the continuing reduction of water levels in at least one major reservoir on the western Great Plains exposed suitable nesting habitat for Piping and Snowy Plovers.The reporting regions noted a potpourri of weather conditions, as is usual.AI the high end of the moisture continuum was Hawaii, which recorded its wettest spring since 1997.The Pacific Coast and northern Rockies generally reported warm and dry conditions, especially in April, leading to numerous early arrival dates as far north as Alaska.Late-arriving migrants, however, were slowed in these regions, as a series of May storms brought cooler temperatures and much-needed moisture--but, in the case of several late-season snowstorms, too cool for many insectivorous species.In much of the East, the weather was warm and dry right through most of the spring, with most regions reporting essentially no fallouts of migrants south of the Great Lakes and New England.Florida recorded only minor fallouts during April, while farther north along the Atlantic Coast conditions were poorer still for birders hoping to witness migration.However, the persistent southerly airflows from April through at least mid-May were perhaps responsible for a better-than-average showing of southern species as far north as Maritime Canada and the Great Lakes region.Included in this mix were reports of Anhingas in Connecticut, Maryland, New Hampshire, and Wisconsin, Wilson's Plovers in upstate New York, Ontario, and Wisconsin, a Brown Pelican in Indiana, a White Ibis in Massachusetts-and Painted Buntings nearly everywhere: across the northern tier of the United States from Minnesota to Maine, and in Canada from Ontario and Quebec (and even Saskatchewan}).Though it is impossible to link any of these appearances conclusively to particular weather systems, as is true for records of kites and doves out of range (Brinkley 2003), their arrivals did often coincide with periods of southerly wind.Overall, though, most of these records, viewed interannually, appear to relate to climate change rather than the caprice of weather--Alaskaõ first Dickcissel.a territorial male rather than a feeder bird, makes the point well.The weather patterns in the continents center were more complex this spring than on the Atlantic Coast.Around the Great Lakes, Great Plains, and Gulf Coast, northerly winds of several nmjor systems produced some notable fallouts, especially along the western Gulf of Mexico coastlines.The most productive of these occurred on 26 April along the central and western Gulf and on 2 May along the western Gulf coasts.Maritime Canada also saw a stalled low-pressure system in late May: cool and wet condiuons caused significant avian mortality at Grand Manan Island, New Brunswick, for instance, and probably much more widely than was observed.Despite the notoriety of several of the springs migrant fallouts, the flavor of the 2004 spring season might be better characterized as a series of expansions: a few widespread species continued to fill gaps in their ranges, southern and southwestern species showed continued signs of expanding or pioneering northward, and several Eurasian species with expanding populations turned up as vagrants on our shores.PASSERINES This spring saw notable extralimital flights of several species of songbird, particularly warblers.A series o[ low-pressure systems moving east in late April and early May produced large fallouts along the central and western Gulf Coast, with adjectives hardly used in recent seasons--"spectacular" in 324 NORTH

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