Spatial Aggregation of Forest Songbird Territories and Possible Implications for Area Sensitivity

Habitat area requirements of forest songbirds vary greatly among species, but the causes of this variation are not well understood. Large area requirements could result from advantages for certain species when settling their territories near those of conspecifics. This phenomenon would result in spatial aggregations much larger than single territories. Species that aggregate their territories could show reduced population viability in highly fragmented forests, since remnant patches may remain unoccupied if they are too small to accommodate several territories. The objectives of this study were twofold: (1) to seek evidence of territory clusters of forest birds at various spatial scales, lags of 250-550 m, before and after controlling for habitat spatial patterns; and (2) to measure the relationship between spatial autocorrelation and apparent landscape sensitivity for these species. In analyses that ignored spatial variation of vegetation within remnant forest patches, nine of the 17 species studied significantly aggregated their territories within patches. After controlling for forest vegetation, the locations of eight out of 17 species remained significantly clustered. The aggregative pattern that we observed may, thus, be indicative of a widespread phenomenon in songbird populations. Furthermore, there was a tendency for species associated with higher forest cover to be more spatially aggregated [ERRATUM].

Movements and Habitat Use by Temperate-Nesting Canada Geese During the Postbreeding Period in Southern Québec

Individual behavior that reduces vulnerability to predation can affect population dynamics of animals. Temperate-nesting Canada Geese (Branta canadensis maxima) have increased steadily throughout the Atlantic flyway and have become a nuisance in some parts of their range. The objective of our study was to describe movements and habitat use during the postbreeding period of Canada Geese recently established in southern Québec. More specifically, we wanted to determine whether geese were using areas where hunting was allowed to assess the potential of harvest to control the number of geese. We tracked a sample of geese fitted with radio or conventional alphanumeric collars throughout the fall in three zones characterized by different habitats and hunting pressure. Before the hunting season, geese left the breeding area where hunting was allowed to reach suburban areas where firearm discharge was prohibited or hunters’ numbers were low. These postbreeding movements occurred when juveniles were approximately three months old. We observed few local movements among zones once migrant geese from northern breeding populations reached the study area. Radio-collared geese used mainly natural habitats (75.4 ± 2.6%), followed by urban (14.4 ± 2.7%), and agricultural habitats (10.3 ± 0.8%). They were located 73.8 ± 6.2% of the time in areas where hunting was prohibited. Geese that attended their juveniles during brood rearing were more prone to use areas where firearm discharge was restricted than geese that had abandoned or lost their brood. This study shows that under the prevailing regulations, the potential of hunting to manage the increasing breeding population of Canada Geese in southern Québec is limited.

Changes in heron and egret populations on the Laurentian Great Lakes and connecting channels, 1977-2009

Canadian and U.S. federal wildlife agencies completed four decadal surveys, spanning the years 1977 to 2009, to census colonial waterbirds breeding on the Great Lakes and adjoining bodies of water. In this paper, we reports abundance, distribution, and general population trends of three species: Black-crowned Night-Heron (Nycticorax nycticorax), Great Egret (Ardea alba), and Great Blue Heron (Ardea herodias). Estimates of nest numbers ranged from approximately 4000-6100 for the Black-crowned Night-Heron, 250-1900 for the Great Egret, and 3800-6400 for the Great Blue Heron. Average annual rates of change in nest numbers between the first (1977) and fourth (2008) census were −1% for the Black-crowned Night-Heron, +23% for the Great Egret, and −0.27% for the Great Blue Heron. Across the 30-year census, Black-crowned Night-Heron estimates decreased in U.S. (−57%) but increased (+18%) in Canadian waters, Great Egret nests increased 1381% in Canadian waters with a smaller, but still substantial increase in the number of nests at U.S. colonies (+613%), and Great Blue Heron numbers increased 148% in Canadian waters and 713% in U.S. waters. Although a single factor cannot be clearly linked to changes observed in each species’ distribution, hydrological variation, habitat succession, nest competition with Double-crested Cormorants (Phalacrocorax auritus), and land use changes likely all contributed. Management activities should support both breeding and foraging conditions including restoration of early successional habitats and anticipate continued northward expansions in the distributions of these waterbirds.