Observatoire dOiseaux de Tadoussac

Les Bergeronnes, Canada

Observatoire dOiseaux de Tadoussac

Les Bergeronnes, Canada
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Savard J.-P.L.,Environment Canada | Melanie C.,Environment Canada | Bruno D.,Observatoire dOiseaux de Tadoussac | Bruno D.,Environment Canada
Ecoscience | Year: 2011

The rusty blackbird (Euphagus carolinus) has received much attention during the last decade, in part due to drastic population declines. We analyzed data from 15 y of fall migration monitoring at the Observatoire d'oiseaux de Tadoussac (OOT), located at the mouth of the Saguenay River on the north shore of the St. Lawrence River estuary in Quebec, Canada. The trend observed suggest an ongoing decline. Numbers of rusty blackbirds varied considerably between years, with peak movements occurring at 5-y intervals and possibly reflecting high reproductive success for those years. The numbers of adult boreal owls caught and banded at the OOT, and the proportion of juveniles, were negatively and positively correlated with rusty blackbird numbers, respectively. Peaks in rusty blackbird abundance occurred when red-backed voles (Clethrionomys gapperi) were abundant in the eastern boreal forest. Also, rusty blackbird numbers were positively correlated to the annual and winter North Atlantic Oscillation (NAO) indices and negatively to the combined precipitation for June, July, and August, suggesting that environmental factors may have contributed both directly and indirectly (through food web processes) to the cyclic variations in abundance observed. Current declines may be exacerbated by NAO fluctuation patterns, that is, more frequent negative indices may negatively affect reproductive success and possibly winter survival.

Gagnon F.,University of Quebec at Chicoutimi | Gagnon F.,Environment Canada | Belisle M.,Observatoire Doiseaux de Tadoussac | Belisle M.,Université de Sherbrooke | And 4 more authors.
Auk | Year: 2010

Using a Canadian weather surveillance radar (CWSR), we assessed the relationship between aural passerine counts and radar reflectivity during autumn migration on 16 nights. Reflectivity was positively correlated on all but 1 night with the number of birds detected aurally, but the correlation strength varied between -0.58 and 0.93 among nights (mean ± SD = 0.69 ± 0.42). Using linear mixed-effects models with aural counts nested within nights, we found that the number of birds detected by observers increased with reflectivity. The slope of this relationship did not vary between observers, nor was it affected by time since sunset, but the number of birds detected aurally tended to be lower when ambient noise levels were high. We know that the radar was relatively sensitive to low bird densities, because the intercept was slightly positive and its 95% confidence interval marginally included zero. However, the relationship between the number of birds detected aurally and reflectivity varied significantly among nights. Such variation was likely caused by a combination of (interacting) factors, including bird species and behavior (e.g., calling rate, flight altitude), influencing bird detectability by the observers and the radar. The weather radar network of the United States (NEXRAD) is already used for bird migration studies, and we conclude that the use of CWSR can extend NEXRAD's coverage farther north by hundreds of kilometers, thereby increasing our understanding of how birds use the North American landscapes during migration. © 2010 The American Ornithologists' Union.

Gagnon F.,Environment Canada | Gagnon F.,University of Quebec at Chicoutimi | Ibarzabal J.,University of Quebec at Chicoutimi | Savard J.-P.L.,Observatoire dOiseaux de Tadoussac | And 5 more authors.
Auk | Year: 2011

We modeled migration intensity as a function of weather, using nightly migration measurements from Doppler surveillance weather radar during autumn migration on the north (Côte-Nord) and south (Gaspésie) shores of the St. Lawrence estuary, Québec, Canada. The radar had negative elevation angles, an uncommon characteristic among weather radars, which allowed simultaneous low-altitude monitoring of bird migration on each side of the estuary. Precipitation and wind both had strong effects on the intensity of migration. Very few birds migrated when >40% of the area had precipitation, especially when winds were strong. Light winds were associated with the strongest migration intensity, regardless of wind direction; in stronger winds, migration was likely only when winds were predominantly from the north. Days immediately after adverse weather events, which are assumed to lead to an accumulation of migrants, were associated with an increase in the intensity of migration in Côte-Nord, but not in Gaspésie. Time since the passage of a cold front had no effect in either region. Bird flight direction and behavior in relation to wind differed on each side of the estuary. On Côte-Nord, birds tended to migrate in a southwesterly direction along the St. Lawrence north coast, in a direction relatively unaffected by wind direction; they compensated or overcompensated for wind drift by following the coast. By contrast, birds in Gaspésie tended to fly in a more southerly direction. They migrated partially or almost fully downwind with only limited compensation, their flight direction often changing with wind direction. © The American Ornithologists' Union, 2011.

Gagnon F.,Environment Canada | Gagnon F.,University of Quebec at Chicoutimi | Ibarzabal J.,University of Quebec at Chicoutimi | Savard J.-P.L.,Observatoire doiseaux de Tadoussac | And 4 more authors.
Canadian Journal of Zoology | Year: 2011

We documented the pattern of nocturnal passerine migration on each side of the St. Lawrence estuary (CôteNord north and Gaspésie south), using the Doppler Canadian weather surveillance radar of Val d'Irène (XAM). We examined whether autumnal migrants flew across the St. Lawrence, resulting in a uniform broad-front migration, or avoided crossing it, resulting in a bird concentration along the north coast. We found that a proportion of migrants crossed the estuary but that most followed the north coast. Ranges at which birds were detected were, on average, greater on Côte-Nord, thereby rejecting the uniform broad-front migration hypothesis, inasmuch as reflectivity measurements suggested that bird concentrated along Côte-Nord. The mean flight direction on Côte-Nord was southwest but shifted westward as the night progressed, avoiding crossing the estuary by late night. In Gaspésie, the mean flight direction over land was south and no directional shift was observed throughout the night. Flight altitude reach up to 1000 m above sea level (a.s.l.), but migratory activity was highest in the first 500 m a.s.l. It appears that the St. Lawrence estuary acts as a leading line and a barrier for nocturnal passerine migrants, and likely shapes migration farther south in Canada and in the United States.

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