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Bird Observatory (bird + observatory)
Selected AbstractsChanges in the timing of spring and autumn migration in North American migrant passerines during a period of global warmingIBIS, Issue 2 2005ALEXANDER M. MILLS Butler (2003) used first arrival dates (FADs) of 103 migrant birds in northeastern USA and found that both long-distance migrants (LDMs; wintering south of the USA) and short-distance migrants (SDMs; wintering in the southern USA) arrived earlier in the second half of the 20th century than they had in the first, consistent with scenarios of global warming; the trend was stronger in SDMs. Using FADs to characterize migration systems can be problematic because they are data from one tail of a distribution, they comprise a mostly male population and they may not correlate well with the balance of the migration period. FADs also provide no information about autumn migration. This paper uses a banding dataset from Long Point Bird Observatory, Ontario, for 14 passerines for a period of global warming (1975,2000), taking these issues into account. The data were filtered to minimize effects of unequal netting effort (147 491 resulting records), and the passage dates then calculated in each season of each year for the 1st, 2nd and 3rd quartiles for regression analysis. Only two of 13 species analysed in the spring showed significantly earlier passage times, although the overall trend was towards earlier spring migration, especially among SDMs. Autumn responses were more prevalent, however, and in some cases more dramatic with six of 13 species showing delayed migration (four SDMs, two LDMs). Two LDMs exhibited earlier autumn migration. Where earlier spring migration occurred, both sexes appeared to contribute to the change. Where delayed migration occurred in autumn, both sexes and both adults and hatch-year birds appeared to contribute in at least some cases. The spring FAD results are consistent with those of Butler, but when the whole migration is considered, change is far from universal in spring and is in fact more substantial and complex in autumn. [source] Within night correlations between radar and ground counts of migrating songbirdsJOURNAL OF FIELD ORNITHOLOGY, Issue 2 2008Michael L. Peckford ABSTRACT Studies comparing numbers of nocturnal migrants in flight with numbers of migrants at stopover sites have produced equivocal results. In 2003, we compared numbers of nocturnal migrants detected by radar to numbers of passerines observed at the Atlantic Bird Observatory in southwestern Nova Scotia, Canada. Numbers of nocturnal migrants detected by radar were positively correlated with numbers of migrants as determined by mist-netting, censuses, and daily estimated totals (daily estimates of birds present based netting and census results and casual observations) the following day. On nights with winds favorable for migration (tailwinds), the peak correlation between ground counts and radar counts the night before occurred just after sunset. On nights with unfavorable winds (headwinds), the correlation increased through the night, with a peak just before sunrise. The patterns of correlation are consistent with a scenario where birds accumulate at the coastline during periods of unfavorable wind, likely because they are not willing to cross a major ecological barrier, the Gulf of Maine. On nights with favorable winds, many birds departed, but some, possibly after testing wind conditions, apparently decided not to cross the Gulf of Maine and returned. Our results suggest that combining data collected using different methods to generate a daily estimated total provides the best estimate of the number of migrants present at a stopover site. Simultaneous studies at multiple locations where different census methods are used, making more effective use of temporal data (both from radar and diurnal counts), will more clearly elucidate patterns of flight behavior by migratory songbirds and the relationship between ground counts and counts of birds aloft. SINOPSIS Estudios cuales comparan los números de aves migratorias en vuelo durante la noche con los números de aves migratorias en sitios de reposo han producido resultados desiguales. En el 2003, comparamos los números de aves migratorias nocturnas detectadas por radar con los números de aves de Passeriformes observadas en el Atlantic Bird Observatory en el sudoeste de Nueva Escocia, Canadá. Los números de aves migratorias detectadas por radar fueron positivamente correlacionados con los números de aves migratorias detectadas mediante la captura con redes de neblina, por censos y por estimaciones diarias totales (el número de aves migratorias basado en capturas, censos y observaciones no-estandarizadas) durante el próximo día. En noches con vientos favorables para la migración (vientos de cola), el punto máximo de la correlación entre los conteos hechos en la tierra con los conteos hechas mediante radar durante la noche anterior ocurrió justo después de la puesta del sol. En noches con vientos no-favorables para la migración (vientos de frente), la correlación incrementó durante la noche, con un punto máximo justo antes del amanecer. Los patrones de las correlaciones son consistentes con una situación en la cual las aves se acumulan sobre la costa del mar durante periodos de viento no-favorables, probablemente porque no están dispuestos a cruzar una barrera ecológica de mayor tamaño, cual es el Golfo de Maine. En noches con vientos favorables, muchas aves partieron, pero algunos, posiblemente después de probar las condiciones de viento, aparentemente decidieron no cruzar el Golfo de Maine y retornaron. Nuestros resultados sugieren que una combinación de datos colectados utilizando diferentes métodos para generar una estimación diaria total provee la mejor estimación del número de aves migratorias presentes en un sitio de reposo. Estudios simultáneos hechos en múltiples sitios donde diferentes métodos de censo son utilizados, realizando un uso mas efectivo de los datos tomados a través del tiempo (provenientes de conteos mediante radar así como de observadores durante el día), mostrarán mas claramente cuales son los patrones del vuelo de las aves migratorias y la relación entre los conteos hechos en la tierra y los conteos de aves en alto vuelo. [source] Climate patterns and the stochastic dynamics of migratory birdsOIKOS, Issue 3 2002Niclas Jonzén We analyse time series data of 17 bird species trapped at Ottenby Bird Observatory, Sweden, during spring migration 1972,1999. The species have similar demography but respond differently to variation in the North Atlantic Oscillation (NAO) , a strong determinant of winter climate in the northern Hemisphere. Species wintering in northern Europe, compared to species having winter quarters in the Mediterranean area, tend to respond positively to variation in NAO. The variation within each group is high due to wide-ranging winter-distribution in many species, probably smoothing out the effect of spatial variation in NAO. Whereas mild winters (high NAO) is benign for many , but not all , birds wintering in northern Europe, the effect of drier-than-normal conditions in the Mediterranean area during high NAO index winters are uncertain. The work presented here goes beyond simple correlative studies and help identifying which species that are most affected by variation in winter climate. This is a first important step that calls for a more mechanistic approach when analysing possible changes to climate change. [source] Climatic responses in spring migration of boreal and arctic birds in relation to wintering area and taxonomyJOURNAL OF AVIAN BIOLOGY, Issue 5 2006Kalle Rainio Large-scale climate fluctuations, such as the North Atlantic Oscillation (NAO), have a marked effect on the timing of spring migration of birds. It has however been suggested that long-distance migrants wintering in Africa could respond less to NAO than short-distance migrants wintering in Europe, making them more vulnerable to climatic changes. We studied whether migratory boreal and arctic bird species returning from different wintering areas show differences in responses to the NAO in the timing of their spring migration. We used data on 75 species from two bird observatories in northern Europe (60°N). By extending the examination to the whole distribution of spring migration and to a taxonomically diverse set of birds, we aimed at finding general patterns of the effects of climate fluctuation on the timing of avian migration. Most species arrived earlier after winters with high NAO index. The degree of NAO-response diminished with the phase of migration: the early part of a species' migratory population responded more strongly than the later part. Early phase waterfowl responded strongest to NAO, but in later phases their response faded to non-significant. This pattern may be related to winter severity and/or ice conditions in the Baltic. In the two other groups, gulls and waders and passerines, all phases of migration responded to NAO and fading with phase was non-significant. The difference between waterfowl and other groups may be related to differences between the phenological development of their respective macrohabitats. Wintering area affected the strength of NAO response in a complicated way. On average medium distance migrants responded most strongly, followed by short-distance migrants and partial migrants. Our results concerning the response of long-distance migrants were difficult to interpret: there is an overall weak yet statistically significant effect, but patterns with phase of migration need further study. Our results highlight the importance of examining the whole distribution of migration and warrant the use of data sets from several sampling sites when studying climatic effects on the timing of avian life-history events. [source] | ||||||||||