Jean-François Giroux

LANDSCAPE-SCALE DISTURBANCES AND CHANGES IN BIRD COMMUNITIES OF BOREAL MIXED-WOOD FORESTS

Bird community response to both landscape-scale and local (forest types) changes in forest cover was studied in three boreal mixed-wood forest landscapes modified by different types of disturbances: (1) a pre-industrial landscape where human settlement, agriculture, and logging activities date back to the early 1930s, (2) an industrial timber managed forest, and (3) a forest dominated by natural disturbances. Birds were sampled at 459 sampling stations distributed among the three landscapes. Local habitat and landscape characteristics of the context surrounding each sampling station (500-m and 1-km radius) were also computed. Bird communities were influenced by landscape-scale changes in forest cover. The higher proportion of early-successional habitats in both human-disturbed landscapes resulted in significantly higher abundance of early-successional bird species and generalists. The mean number of mature forest bird species was significantly lower in the industrial and pre-industrial landscapes than in the natural landscape. Landscape-scale conversion of mature forests from mixed-wood to deciduous cover in human-disturbed landscapes was the main cause of changes in mature forest bird communities. In these landscapes, the abundance of species associated with mixed and coniferous forest cover was lower, whereas species that preferred a deciduous cover were more abundant. Variation in bird community composition determined by the landscape context was as important as local habitat conditions, suggesting that predictions on the regional impact of forest management on songbirds with models solely based on local scale factors could be misleading. Patterns of bird species composition were related to several landscape composition variables (proportions of forest types), but not to configuration variables (e.g., interior habitat, amount of edge). Overall, our results indicated that the large-scale conversion of the southern portion of the boreal forest from a mixed to a deciduous cover may be one of the most important threats to the integrity of bird communities in these forest mosaics. Negative effects of changes in bird communities could be attenuated if current forestry practices are modified toward maintaining forest types (deciduous, mixed-wood, and coniferous) at levels similar to those observed under natural disturbances.

Body Condition, Migration, and Timing of Reproduction in Snow Geese: A Test of the Condition-Dependent Model of Optimal Clutch Size

The seasonal decline of avian clutch size may result from the conflict between the advantage of early breeding (greater offspring value) and the advantage of a delay in lay date (improved body condition and hence clutch size). We tested predictions of a condition‐dependent individual optimization model based on this trade‐off (Rowe et al. 1994) in a long‐distance migrant, the greater snow goose (Chen caerulescens atlantica), using data on condition, migration, and reproductive decisions of individuals. We closely tracked radio‐marked females at their main spring staging area and on their breeding grounds. Our results were consistent with predictions of the model. Early‐arriving females had a longer prelaying period and initiated their nests earlier than late arrivals. After controlling statistically for arrival date, we determined that females with high premigration condition had an earlier lay date than those in low condition. After controlling for the seasonal decline (i.e., lay date), we observed that clutch size was not related to premigration condition. Moreover, we took advantage of an unplanned manipulation of the prebreeding condition that occurred during our long‐term study. We found that a reduction in condition caused a delay in lay date. However, after controlling for the seasonal decline, it did not affect clutch size. Our study indicates that geese simultaneously adjust their lay date and clutch size according to their premigration condition and migratory behavior as predicted by the condition‐dependent optimization model.

Individual variation in timing of migration: causes and reproductive consequences in greater snow geese (Anser caerulescens atlanticus)

Decisions made by birds during migration to breeding grounds can strongly affect the fitness of individuals. We investigated possible causes and reproductive consequences of inter-individual variation in the migratory behavior of an arctic-nesting species, the greater snow goose (Anser caerulescens atlanticus), by radio-tracking females at their staging area and on their breeding grounds. Females showed relatively high repeatability in the duration of migration (ri=0.37) and arrival date on the breeding grounds (ri=0.42) suggesting that these traits are characteristics of individuals. Conversely, no individual consistency in departure date from the staging area was detected (ri=−0.02) indicating that environmental factors may have a large influence. Females paired with dominant males departed slightly earlier from the staging area than females accompanied by subordinate males. However, neither social status on the staging area (i.e. paired vs unpaired) nor dominance scores were associated with arrival time of individuals. Finally, the probability of breeding was positively related to arrival date indicating a reproductive cost of arriving too early on the breeding grounds. The combination of breeding probability and seasonal decline in breeding success nonetheless suggests that females arriving a few days earlier than the median arrival date attained highest reproductive success. Our results show that assessing the fitness consequences of early arrival by focusing solely on breeding females would lead to an overestimation of the genuine benefits. This study also indicates possible genetically based differences among individuals in migration duration and arrival time on the breeding grounds.

Trophic Interactions in a High Arctic Snow Goose Colony

Abstract We examined the role of trophic interactions in structuring a high arctic tundra community characterized by a large breeding colony of greater snow geese (Chen caerulescens atlantica). According to the exploitation ecosystem hypothesis of Oksanen et al. (1981), food chains are controlled by top-down interactions. However, because the arctic primary productivity is low, herbivore populations are too small to support functional predator populations and these communities should thus be dominated by the plant/ herbivore trophic-level interaction. Since 1990, we have been monitoring annual abundance and productivity of geese, the impact of goose grazing, predator abundance (mostly arctic foxes, Alopex lagopus) and the abundance of lemmings, the other significant herbivore in this community, on Bylot Island, Nunavut, Canada. Goose grazing consistently removed a significant proportion of the standing crop (∼40%) in tundra wetlands every year. Grazing changed plant community composition and reduced the production of grasses and sedges to a low-level equilibrium compared to the situation where the presence of geese had been removed. Lemming cyclic fluctuations were strong and affected fox reproduction. Fox predation on goose eggs was severe and generated marked annual variation in goose productivity. Predation intensity on geese was closely related to the lemming cycle, a consequence of an indirect interaction between lemming and geese via shared predators. We conclude that, contrary to the exploitation ecosystem hypothesis, both the plant/herbivore and predator/prey interactions are significant in this arctic community.

SNAG USE BY FORAGING BLACK-BACKED WOODPECKERS (PICOIDES ARCTICUS) IN A RECENTLY BURNED EASTERN BOREAL FOREST

Abstract We studied snag use for foraging by Black-backed Woodpeckers (Picoides arcticus) one year after a fire in an eastern black spruce (Picea mariana) boreal forest in Quebec, Canada. We searched for signs of foraging (bark flaking and excavation holes) by Black-backed Woodpeckers on 6,536 snags sampled in 56 plots located in portions of the burned forest that had not been salvage logged. A logistic regression model was developed based on the presence or absence of foraging signs. Results showed that Black-backed Woodpeckers used larger snags that were less deteriorated by fire (qualified as high-quality snags). Direct field observations of individuals foraging on 119 snags also indicated that used snags corresponded to those of high predicted quality. Finally, we assessed the relationship between food availability and snag characteristics by measuring the density of wood-boring beetle larvae holes on 30 snags of different size and deterioration classes. High-quality snags contained higher prey densities (wood-boring beetle holes) than smaller and more deteriorated snags. We recommend that forest blocks characterized by large and less deteriorated trees be preserved from salvage logging in recently burned boreal forests in northeastern North America.

ARE BODY CONDITION AND REPRODUCTIVE EFFORT OF LAYING GREATER SNOW GEESE AFFECTED BY THE SPRING HUNT

Abstract A spring hunt was implemented on the staging areas of Greater Snow Geese (Chen caerulescens atlantica) in Quebec in 1999 and 2000. We evaluated whether this activity, which occurred during the period of spring nutrient storage, may have affected the body condition and reproductive effort of laying geese. We collected laying females in years with a spring hunt (1999–2000, n = 34) and compared them with birds collected in years without a hunt (1989–1990, n = 10). All indices of body condition and clutch size were significantly lower in years with a hunt than in years without, and laying dates were delayed. Tracking of radio-marked females on the staging and breeding areas showed that a lower proportion of females reached the nesting areas in years with a hunt (28% in 1999–2000, n = 80) than in years without (85% in 1997–1998, n = 80) and that fewer females nested (9% vs. 56%, respectively). Our results suggest that the spring hunt negatively affected nesting geese. ¿Son Afectadas por la Cacería de Primavera la Condición Física y el Esfuerzo Reproductivo de Chen caerulescens atlantica? Resumen. La cacería de primavera fue implementada en áreas de escala de Chen caerulescens atlantica en Quebec en 1999 y 2000. Evaluamos si la cacería, que se llevó a cabo durante el período primaveral de acumulación de nutrientes, pudo haber afectado la condición fisica y el esfuerzo reproductivo de los gansos. Colectamos hembras que estuvieran poniendo huevos en años con cacería de primavera (1999–2000, n = 34) y las comparamos con aves colectadas en años sin cacería (1989–1990, n = 10). Todos los índices de la condición física y del tamaño de la nidada fueron significativamente menores en años con cacería que en años sin cacería, y se retrasaron las fechas de puesta. El seguimiento de hembras marcadas con radio en áreas de escala y cría mostró que una menor proporción llegó a las áreas de nidificación en años con cacería (28% en 1999–2000, n = 80) que en años sin cacería (85% en 1997–1998, n = 80), y que menos hembras nidificaron (9% vs. 56%, respectivamente). Nuestros resultados sugieren que la cacería de primavera afecta negativamente a los gansos nidificantes.

Effect of A spring hunt on nutrient storage by greater snow geese in southern Quebec

A spring conservation hunt (15 Apr-31 May) to control the exponential population growth of greater snow geese (Chen caerulescens atlantica) was introduced in 1999 during their staging in southern Quebec, Canada. We tested the hypothesis that disturbance by hunting negatively affected nutrient storage in spring. We compared the amount of fat and protein stored by staging geese during the hunt (1999 and 2000) to similar data obtained sporadically between 1979 and 1998 (no hunt). We collected adult females at 3 sites along the St. Lawrence River during years with (n = 235 geese) and without (n = 194) hunting. We used abdominal fat and dry breast muscle mass as corresponding indices of fat and protein reserves. The condition of geese arriving at the staging area did not differ between years with and without a hunt. Abdominal fat of geese at the end of the staging period was 29-48% lower (depending on site and year) during years with a hunt than in years without. Similarly, breast muscles of geese at the end of staging were 5-11% lighter in years with a spring hunt. Low stable-carbon isotope ratios (δ 13 C) in tissues of geese collected in spring 1999 suggested that they fed less on corn, a C4 plant and a major food source for geese, than in other years. This may have contributed to their reduced body condition that year. However, despite high δ 13 C values in 2000, indicative of a high proportion of corn in the diet, nutrient storage in geese was still reduced compared to years without a hunt. We conclude that hunting was the most important factor explaining the low fat and protein storage of geese in springs of 1999 and 2000. We suggest that hunting disturbance reduced nutrient storage of geese because of decreased feeding activity and increased flying time.

Predator behaviour and predation risk in the heterogeneous Arctic environment

1. Habitat heterogeneity and predator behaviour can strongly affect predator-prey interactions but these factors are rarely considered simultaneously, especially when systems encompass multiple predators and prey. 2. In the Arctic, greater snow geese Anser caerulescens atlanticus L. nest in two structurally different habitats: wetlands that form intricate networks of water channels, and mesic tundra where such obstacles are absent. In this heterogeneous environment, goose eggs are exposed to two types of predators: the arctic fox Vulpes lagopus L. and a diversity of avian predators. We hypothesized that, contrary to birds, the hunting ability of foxes would be impaired by the structurally complex wetland habitat, resulting in a lower predation risk for goose eggs. 3. In addition, lemmings, the main prey of foxes, show strong population cycles. We thus further examined how their fluctuations influenced the interaction between habitat heterogeneity and fox predation on goose eggs. 4. An experimental approach with artificial nests suggested that foxes were faster than avian predators to find unattended goose nests in mesic tundra whereas the reverse was true in wetlands. Foxes spent 3.5 times more time between consecutive attacks on real goose nests in wetlands than in mesic tundra. Their attacks on goose nests were also half as successful in wetlands than in mesic tundra whereas no difference was found for avian predators. 5. Nesting success in wetlands (65%) was higher than in mesic tundra (56%) but the difference between habitats increased during lemming crashes (15%) compared to other phases of the cycle (5%). Nests located at the edge of wetland patches were also less successful than central ones, suggesting a gradient in accessibility of goose nests in wetlands for foxes. 6. Our study shows that the structural complexity of wetlands decreases predation risk from foxes but not avian predators in arctic-nesting birds. Our results also demonstrate that cyclic lemming populations indirectly alter the spatial distribution of productive nests due to a complex interaction between habitat structure, prey-switching and foraging success of foxes.

Use of farmland riparian strips by declining and crop damaging birds

Abstract Riparian strips prevent river bank erosion, help to maintain water quality, and contribute to the maintenance of biodiversity in agro-ecosystems. These areas are often perceived by farmers as potential breeding habitats of animals and plants that are harmful to crops. Consequently, the vegetation in riparian strips is periodically subjected to grazing, mowing, burning and/or herbicide spraying. Bird use was compared among six types of farmland riparian strips (grazed, grassy herbaceous, non-grassy herbaceous, low shrubby, tall shrubby, and wooded) in the agricultural landscape of southern Quebec (Canada). These strip types constituted a gradient with respect to plant diversity, vegetal structure, and plant cover control or disturbance. The objectives of this study were to document the avian communities of these riparian strip habitats to determine (1) their respective contribution to bird conservation and (2) their role as potential breeding habitats for crop damaging bird species. Bird abundance and species richness were greater in the wooded and tall shrubby strips than in the other riparian strips. Abundance of crop damaging species was significantly greater in wooded strips than in any other type; however, Red-winged Blackbirds, the most abundant bird species recorded and the species most likely to damage crops in the study area, did not differ in abundance among the six strip types, nor in adjacent crop fields. Diversified riparian strip habitats that include trees and tall shrubs can contribute to the preservation of avian diversity in agricultural landscapes, without providing significant breeding habitats for birds harmful to agriculture.

Tug of war between continental gene flow and rearing site philopatry in a migratory bird: the sex‐biased dispersal paradigm reconsidered

Nonrandom dispersal has been recently advanced as a mechanism promoting fine‐scale genetic differentiation in resident populations, yet how this applies to species with high rates of dispersal is still unclear. Using a migratory species considered a classical example of male‐biased dispersal (the greater snow goose, Chen caerulescens atlantica), we documented a temporally stable fine‐scale genetic clustering between spatially distinct rearing sites (5–30 km apart), where family aggregates shortly after hatching. Such genetic differentiation can only arise if, in both sexes, dispersal is restricted and nonrandom, a surprising result considering that pairing occurs among mixed flocks of birds more than 3000 km away from the breeding grounds. Fine‐scale genetic structure may thus occur even in migratory species with high gene flow. We further show that looking for genetic structure based on nesting sites only may be misleading. Genetically distinct individuals that segregated into different rearing sites were in fact spatially mixed during nesting. These findings provide new, scale‐dependent links between genetic structure, pairing, and dispersal and show the importance of sampling different stages of the breeding cycle in order to detect a spatial genetic structure.