Craig S. Machtans

ARE BOREAL BIRDS RESILIENT TO FOREST FRAGMENTATION? AN EXPERIMENTAL STUDY OF SHORT-TERM COMMUNITY RESPONSES

We studied the effect of habitat fragmentation on the richness, diversity, turnover, and abundance of breeding bird communities in old, boreal mixed-wood forest by creating isolated and connected forest fragments of 1, 10, 40, and 100 ha. Connected fragments were linked by 100 m wide riparian buffer strips. Each size class within treatments and controls was replicated three times. We sampled the passerine community using point counts before, and in each of two years after, forest harvesting, accumulating 21340 records representing 59 species. We detected no significant change in species richness as a result of the harvesting, except in the 1-ha connected fragments, where the number of species increased two years after isolation. This increase was accounted for by transient species, suggesting that the adjacent buffer strips were being used as movement corridors. Diversity (log series alpha index) was dependent on area in the isolated fragments only after cutting, having decreased in the smaller areas. Tur...

A Synthesis of Human-related Avian Mortality in Canada

Many human activities in Canada kill wild birds, yet the relative magnitude of mortality from different sources and the consequent effects on bird populations have not been systematically evaluated. We synthesize recent estimates of avian mortality in Canada from a range of industrial and other human activities, to provide context for the estimates from individual sources presented in this special feature. We assessed the geographic, seasonal, and taxonomic variation in the magnitude of national-scale mortality and in population-level effects on species or groups across Canada, by combining these estimates into a stochastic model of stage-specific mortality. The range of estimates of avian mortality from each source covers several orders of magnitude, and, numerically, landbirds were the most affected group. In total, we estimate that approximately 269 million birds and 2 million nests are destroyed annually in Canada, the equivalent of over 186 million breeding individuals. Combined, cat predation and collisions with windows, vehicles, and transmission lines caused > 95% of all mortality; the highest industrial causes of mortality were the electrical power and agriculture sectors. Other mortality sources such as fisheries bycatch can have important local or species-specific impacts, but are relatively small at a national scale. Mortality rates differed across species and families within major bird groups, highlighting that mortality is not simply proportional to abundance. We also found that mortality is not evenly spread across the country; the largest mortality sources are coincident with human population distribution, while industrial sources are concentrated in southern Ontario, Alberta, and southwestern British Columbia. Many species are therefore likely to be vulnerable to cumulative effects of multiple human-related impacts. This assessment also confirms the high uncertainty in estimating human-related avian mortality in terms of species involved, potential for population-level effects, and the cumulative effects of mortality across the landscape. Effort is still required to improve these estimates, and to guide conservation efforts to minimize direct mortality caused by human activities on Canada’s wild bird populations. As avian mortality represents only a portion of the overall impact to avifauna, indirect effects such as habitat fragmentation and alteration, site avoidance, disturbance, and related issues must also be carefully considered.

Effects of forest regeneration on songbird movements in a managed forest landscape of Alberta, Canada

Recent studies have shown that barrier effects exist even in relatively vagile species such as forest songbirds. The objectives of this study were to determine whether a 560 × 100 m riparian buffer strip of mature forest was used as a movement corridor by forest songbirds and, if so, to what extent corridor effects persisted as woody vegetation regenerated in the adjacent clearcut. Over a 4-yr period, juvenile movement rates decreased in the riparian buffer strip and increased in the regenerating clearcut. Adult movement rates increased in the riparian buffer strip in the first year after logging, then gradually decreased, while still increasing in the regenerating clearcut. However, both juvenile and adult movement rates were higher in the buffer strip than in an undisturbed control site. Results suggest that most adults we captured held territories in the vicinity of the net lanes,and that most of the juveniles captured were dispersing away from their natal territory. Four years after harvest, juvenile movement rates were higher in the regenerating clearcut than in the riparian buffer strip, but several species had not yet been captured or detected in the regeneration. Our results suggest that the use of the riparian buffer strip as a movement corridor decreased with forest regeneration for both adults and juveniles. However, the buffer strip still acted as a movement corridor for the following species: Philadelphia and Red-eyed Vireos, Red-breasted Nuthatch, and Ovenbird.

A First Estimate for Canada of the Number of Birds Killed by Colliding with Building Windows

Mortality from birds colliding with windows in buildings may be ecologically significant. Although data are sparse, we estimated the number of birds killed by this means in Canada. We made distinct models for three classes of buildings: houses, low-rise commercial and institutional buildings, and tall buildings. Estimates were developed using Monte Carlo-based simulations incorporating uncertainties and based on distributions that best fit available data or conceptual models. We estimate that about 25 million (range 16 – 42 M) birds are killed by colliding with windows in Canada annually. The assumptions used in our analyses are identified in detail so that subsequent efforts can address the uncertainties. Houses likely cause 90% of building-related mortalities, low-rise buildings slightly less than 10%, and tall buildings approximately 1%. The disproportionate contribution of mortality caused by houses is a function of their relative number compared to the two other classes of buildings. Our review found that warblers and sparrows were the most commonly killed birds at low-rise and tall buildings, and insufficient information exists on species deaths at houses to determine proportions. Targeted mitigation for certain tall buildings and a segment of the low-rise building types could significantly reduce the total mortality for both these building types. Mitigation strategies are now widely available, including architectural guidance produced by numerous cities in North America as well as specific products suitable for home use to reduce the number of birds colliding with windows. RESUME. La mortalite d’oiseaux par collision avec les fenetres de bâtiments pourrait avoir une importance ecologique. Malgre la rarete des donnees, nous avons estime le nombre d’oiseaux morts de cette facon au Canada. Nous avons elabore des modeles distincts pour trois classes de bâtiments : les maisons, les bâtiments commerciaux et institutionnels de faible hauteur, et les edifices. Nos estimations ont ete faites a partir de simulations de Monte-Carlo tenant compte des incertitudes et fondees sur les distributions qui s’ajustaient le mieux aux donnees disponibles ou aux modeles conceptuels. Nous avons estime qu’environ 25 millions (etendue : 16-42 millions) d’oiseaux sont morts a la suite de collisions avec les fenetres chaque annee au Canada. Les hypotheses emises dans notre analyse sont decrites en detail de facon a ce que les efforts subsequents puissent evaluer les incertitudes. Les maisons sont vraisemblablement responsables de 90 % des mortalites relatives aux collisions, les bâtiments de faible hauteur d’un peu moins de 10 % et les edifices d’environ 1 %. La contribution disproportionnee de la mortalite causee par les maisons est attribuable a leur nombre relatif comparativement aux deux autres classes de bâtiments. Selon notre revue de litterature, les parulines et les bruants sont les oiseaux qui se frappent le plus communement sur les bâtiments de faible hauteur et les edifices. Les donnees sont insuffisantes pour etablir la proportion des especes qui se frappent mortellement sur les fenetres de maisons. Des mesures d’attenuation ciblees pour certains edifices et bâtiments de faible hauteur pourraient reduire significativement la mortalite totale sur ces structures. De nos jours, il existe des strategies d’attenuation faciles d’acces, y compris des guides concernant l’architecture produits par de nombreuses villes en Amerique du Nord, de meme que des produits specifiques pour les maisons afin de reduire le nombre d’oiseaux se frappant mortellement dans les fenetres.

BOREAL FOREST SONGBIRD COMMUNITIES OF THE LIARD VALLEY, NORTHWEST TERRITORIES, CANADA

Abstract Songbird communities in the boreal forest of the Liard Valley, Northwest Territories, Canada, are described after three years of study. Point count stations (n = 195) were placed in six types of forest (mature deciduous, coniferous, and mixedwood; young forests; wooded bogs; clearcuts) in a 700-km2 area. Vegetation characteristics at each station were also measured. Eighty-five species of birds (59 passerine species) occurred in 11 647 detections. Mixedwood forests had the highest richness of songbirds (∼41 species per 800 individuals) of the six forest types, and contained approximately 30% more individuals than nearly pure coniferous or deciduous forests. Species richness and relative abundance was 10–50% lower than in comparable forests farther south and east, and the difference was most pronounced in deciduous forests. Communities were dominated by a few species, especially Tennessee Warbler (Vermivora peregrina), Magnolia Warbler (Dendroica magnolia), Swainsons Thrush (Catharus ustulatus), Yellow-rumped Warbler (Dendroica coronata) and Chipping Sparrow (Spizella passerina). White-throated Sparrow (Zonotrichia albicollis), a dominant species in boreal forests farther south, was notably scarce in all forests except clearcuts. Clearcuts and wooded bogs had the simplest communities, but had unique species assemblages. Canonical correspondence analysis showed that the bird community was well correlated with vegetation structure. The primary gradient in upland forests was from deciduous to coniferous forests (also young to old, respectively). The secondary gradient was from structurally simple to complex forests. These results allow comparisons with other boreal areas to understand regional patterns and help describe the bird community for conservation purposes. Comunidades de Aves Canoras de Bosques Boreales del Valle de Liard, Territorios del Noroeste, Canadá Resumen. Luego de tres años de estudio, se describen las comunidades de aves canoras de bosques boreales del Valle de Liard, Territorios del Noroeste, Canadá. Se ubicaron estaciones de conteo de punto (n = 195) en seis tipos de bosque (maduro caducifolio, conífero y de maderas mixtas; bosques jóvenes; pantanos arbolados; zonas taladas) en un área de 700 km2. Las características de la vegetación en cada estación también fueron medidas. Se registraron 85 especies de aves (59 especies de paserinas) en 11 647 detecciones. Los bosques mixtos presentaron la mayor riqueza de aves canoras (∼41 especies por 800 individuos) de los seis tipos de bosque, y contuvieron aproximadamente 30% individuos más que los bosques de coníferas y los caducifolios. La riqueza de especies y la abundancia relativa fue 10–50% menor que en bosques comparables más al sur y al este, y la diferencia fue más pronunciada en los bosques caducifolios. Las comunidades estuvieron dominadas por unas pocas especies, especialmente Vermivora peregrina, Dendroica magnolia, Catharus ustulatus, Dendroica coronata y Spizella passerina. Zonotrichia albicollis, una especie dominante en bosques boreales más al sur, fue notablemente escasa en todos los bosques, excepto en las zonas taladas. Las áreas taladas y los pantanos arbolados tuvieron las comunidades más simples, pero presentaron ensamblajes únicos. Análisis de correspondencia canónica mostraron que la comunidad de aves estuvo bien correlacionada con la estructura de la vegetación. El gradiente primario en bosques de zonas altas fue de bosque caducifolio a conífero (también de joven a viejo, respectivamente). El gradiente secundario fue de bosques estructuralmente simples a bosques complejos. Estos resultados permiten hacer comparaciones con otros bosques boreales para entender los patrones regionales y ayudar a describir las comunidades de aves con fines de conservación.

Direct Effects of Cattle on Grassland Birds in Canada

Effects of grazing on grassland birds are generally thought to be indirect, through alteration of vegetation structure; however, livestock can also affect nest survival directly through trampling and other disturbances (e.g., livestock-induced abandonment). We extracted data on nest fates from 18 grazing studies conducted in Canada. We used these data to assess rates of nest destruction by cattle among 9 ecoregions and between seasonal and rotational grazing systems. Overall, few nests were destroyed by cattle (average 1.5% of 9132 nests). Nest destruction was positively correlated with grazing pressure (i.e., stocking rate or grazing intensity), but nest survival was higher in more heavily grazed areas for some species. Because rates of destruction of grassland bird nests by cattle are low in Canada, management efforts to reduce such destruction may not be of ecological or economic value in Canada.

Understanding the value of imperfect science from national estimates of bird mortality from window collisions

ABSTRACT The publication of a U.S. estimate of bird–window collisions by Loss et al. is an example of the somewhat contentious approach of using extrapolations to obtain large-scale estimates from small-scale studies. We review the approach by Loss et al. and other authors who have published papers on human-induced avian mortality and describe the drawbacks and advantages to publishing what could be considered imperfect science. The main drawback is the inherent and somewhat unquantifiable bias of using small-scale studies to scale up to a national estimate. The direct benefits include development of new methodologies for creating the estimates, an explicit treatment of known biases with acknowledged uncertainty in the final estimate, and the novel results. Other overarching benefits are that these types of papers are catalysts for improving all aspects of the science of estimates and for policies that must respond to the new information.

Retrospective Comparison of the Occurrence and Abundance of Rusty Blackbird in the Mackenzie Valley, Northwest Territories

Rusty Blackbird is listed as a species of “special concern” by the Committee On the Status of Endangered Wildlife In Canada, and has shown steep population declines in recent decades. Forty-five locations with historical survey data from the 1970s in the Mackenzie Valley, Northwest Territories, Canada were revisited in 2006 to check for changes in the occurrence or abundance of Rusty Blackbird. Our retrospective analysis revealed a number of analytical challenges for such comparisons that we describe. The number of lakes on which this species occurred does not appear to have declined significantly in the past three decades when a correction for survey duration was applied. The range-wide decline of 5.1%/yr based on Christmas Bird Count data would have resulted in 2006 occupancy at ≈5 lakes. We estimate that with correction this would have increased to ≈26. However, naive or unadjusted analyses with a Chi-squared test showed a significant decline. A simulated resampling of the historical data was performed using a repeatability factor of 62% that was derived from a subset of historical lakes that was visited twice in the 1970s. Only 8 of 13 lakes resurveyed had the same results on both historical visits. Our unadjusted 2006 results are a likely outcome, i.e., a 14.9% chance of finding this result, when this repeatability factor is considered, and the likelihood of no change is higher when our corrected data are considered. The possibility of double counting in the historical data further reduced the likelihood of a large decline in relative abundance. Therefore, Rusty Blackbird occurrence does not appear to have changed significantly in the past 33 yr in the Mackenzie Valley. We conclude with a qualitative discussion that supports the notion that declines in the southern parts of their range may be a large factor in the observed rates of population decline. RESUME. Le Quiscale rouilleux fait partie des especes preoccupantes selon le Comite sur la situation des especes en peril au Canada, et ses populations ont subi un declin marque au cours des dernieres decennies. En 2006, nous sommes retournes recenser 45 sites de la vallee du fleuve Mackenzie, Territoires du NordOuest, Canada, pour lesquels il existait des donnees d’inventaire datant des annees 1970, afin de verifier les changements d’occurrence et d’abondance du Quiscale rouilleux. Nous decrivons ici certains problemes que notre analyse retrospective a fait ressortir. Le nombre de lacs ou l’espece etait presente ne semble pas avoir diminue significativement durant les trois dernieres decennies lorsqu’on corrige pour tenir compte de la duree de l’inventaire. Le declin de 5,1 % par annee dans l’ensemble de l’aire, d’apres les donnees du Recensement des oiseaux de Noel, aurait du se traduire par la presence de l’espece a ≈5 lacs en 2006; nous avons plutot detecte l’espece a 21 lacs (≈26 avec la correction). Toutefois, des analyses sans correction au moyen d’un test de chi-carre ont montre un declin significatif. Nous avons simule un re-echantillonnage des donnees historiques a l’aide d’un facteur de repetabilite de 62 %, derive d’un sous-echantillon de lacs qui avaient ete visites a deux reprises dans les annees 1970 (seulement 8 des 13 lacs montraient les memes resultats pour les deux visites). Nos resultats non-corriges de 2006 sont vraisemblables (c.-a-d. qu’ils ont 14,9 % de chance de se produire) lorsque l’on tient compte de ce facteur de repetabilite, tandis que la Canadian Wildlife Service, Environment Canada Avian Conservation and Ecology Ecologie et conservation des oiseaux 2(1): 3 http://www.ace-eco.org/vol2/iss1/art3/ possibilite qu’il n’y ait eu aucun changement est plus elevee lorsqu’on utilise nos donnees corrigees. La possibilite d’un double comptage dans les donnees historiques reduit encore davantage la vraisemblance d’un declin important de l’abondance relative. Ainsi, l’occurrence du Quiscale rouilleux ne semble pas avoir change significativement au cours des 33 dernieres annees dans la vallee du fleuve Mackenzie. Nous concluons avec une discussion qualitative qui soutient l’idee que les declins dans le sud de l’aire de repartition pourraient constituer un element important dans les declins de population rapportes.

How well do regional or national Breeding Bird Survey data predict songbird population trends at an intact boreal site

A study to monitor boreal songbird trends was initiated in 1998 in a relatively undisturbed and remote part of the boreal forest in the Northwest Territories, Canada. Eight years of point count data were collected over the 14 years of the study, 1998-2011. Trends were estimated for 50 bird species using generalized linear mixed-effects models, with random effects to account for temporal (repeat sampling within years) and spatial (stations within stands) autocorrelation and variability associated with multiple observers. We tested whether regional and national Breeding Bird Survey (BBS) trends could, on average, predict trends in our study area. Significant increases in our study area outnumbered decreases by 12 species to 6, an opposite pattern compared to Alberta (6 versus 15, respectively) and Canada (9 versus 20). Twenty-two species with relatively precise trend estimates (precision to detect > 30% decline in 10 years; observed SE ≤ 3.7%/year) showed nonsignificant trends, similar to Alberta (24) and Canada (20). Precision-weighted trends for a sample of 19 species with both reliable trends at our site and small portions of their range covered by BBS in Canada were, on average, more negative for Alberta (1.34% per year lower) and for Canada (1.15% per year lower) relative to Fort Liard, though 95% credible intervals still contained zero. We suggest that part of the differences could be attributable to local resource pulses (insect outbreak). However, we also suggest that the tendency for BBS route coverage to disproportionately sample more southerly, developed areas in the boreal forest could result in BBS trends that are not representative of range-wide trends for species whose range is centred farther north. Les données régionales et nationales du Relevé des oiseaux nicheurs permettent-elles de bien prédire la tendance des populations de passereaux dans un secteur boréal vierge? RÉSUMÉ. Une étude visant à suivre la tendance de passereaux boréaux a été amorcée en 1998 dans une partie relativement peu perturbée et isolée de la forêt boréale des Territoires du Nord-Ouest, au Canada. Nous avons échantillonné des points d’écoute pendant 8 des 14 années qu’a duré l’étude (1998-2011). La tendance a été estimée pour 50 espèces d’oiseaux au moyen de modèles linéaires généralisés à effets mixtes, pour lesquels les effets aléatoires ont tenu compte de l’autocorrélation et de la variabilité temporelles (répétabilité intra-annuelle) et spatiales (stations à l’intérieur des peuplements) associées aux observateurs multiples. Nous avons testé si les tendances régionales et nationales du Relevé des oiseaux nicheurs (BBS) pouvaient, en général, prédire les tendances dans notre aire d’étude. Les hausses significatives (12 espèces) dans l’aire d’étude l’ont emporté sur les baisses (6 espèces), une tendance contraire à celle observée en Alberta (respectivement 6 contre 15) et au Canada (9 contre 20). Vingt-deux espèces ayant des estimations de tendance relativement précises (suffisantes pour détecter un déclin > 30 % sur 10 ans; erreur-type observée ≤ 3,7 %/an) avaient une tendance non significative, un résultat comparable à ceux de l’Alberta (24) et du Canada (20). La tendance pondérée selon la précision pour un ensemble de 19 espèces ayant une tendance fiable dans notre aire d’étude et une faible portion de leur aire couverte par le BBS au Canada était, en moyenne, plus négative pour l’Alberta (inférieur de 1,34 % par année) et le Canada (inférieur de 1,15 % par année) comparativement à Fort Liard, même si les intervalles de crédibilité de 95 % comprenaient encore des zéros. Nous pensons que ces différences de tendance pourraient être en partie imputables à des pics locaux d’abondance des ressources (épidémie d’insectes). Toutefois, nous sommes également d’avis que la tendance des routes du BBS à être disproportionnellement situées dans des endroits plus au sud et en forêt boréale aménagée pourrait faire en sorte que les tendances provenant du BBS ne sont pas représentatives des tendances dans l’ensemble de l’aire chez les espèces dont l’aire de répartition est centrée plus au nord.

Ovenbird ( Seiurus aurocapilla ) Territory Placement Near Seismic Lines is Influenced by Forest Regeneration and Conspecific Density

The boreal forest of western Canada is being dissected by seismic lines used for oil and gas exploration. The vast amount of edge being created is leading to concerns that core habitat will be reduced for forest interior species for extended periods of time. The Ovenbird (Seiurus aurocapilla) is a boreal songbird known to be sensitive to newly created seismic lines because it does not include newly cut lines within its territory. We examined multiple hypotheses to explain potential mechanisms causing this behavior by mapping Ovenbird territories near lines with varying states of vegetation regeneration. The best model to explain line exclusion behavior included the number of neighboring conspecifics, the amount of bare ground, leaf-litter depth, and canopy closure. Ovenbirds exclude recently cut seismic lines from their territories because of lack of protective cover (lower tree and shrub cover) and because of reduced food resources due to large areas of bare ground. Food reduction and perceived predation risk effects seem to be mitigated once leaf litter (depth and extent of cover) and woody vegetation cover are restored to forest interior levels. However, as conspecific density increases, lines are more likely to be used as landmarks to demarcate territorial boundaries, even when woody vegetation cover and leaf litter are restored. This behavior can reduce territory density near seismic lines by changing the spatial distribution of territories. Landmark effects are longer lasting than the effects from reduced food or perceived predation risk because canopy height and tree density take >40 years to recover to forest interior levels. Mitigation of seismic line impacts on Ovenbirds should focus on restoring forest cover as quickly as possible after line cutting. RESUME. La foret boreale de l’ouest du Canada subit un decoupage par les lignes sismiques effectuees dans le cadre de l’exploration petroliere et gaziere. La grande quantite de bordures ainsi creees souleve des preoccupations quant a l’integrite des milieux pour les especes forestieres de massifs continus, et ce, pour de longues periodes. La Paruline couronnee (Seiurus aurocapilla) est un passereau boreal reconnu pour sa sensibilite aux lignes sismiques recemment creees parce qu’elle exclut les bandes nouvellement coupees de son territoire. Afin d’examiner les nombreuses hypotheses pouvant expliquer les mecanismes possibles derriere ce comportement, nous avons cartographie les territoires de parulines situes pres de lignes, selon differents stades de regeneration de la vegetation. Le modele qui explique le mieux le comportement d’exclusion des lignes inclut le nombre de conspecifiques voisins, la superficie de sol nu, la profondeur de la litiere forestiere et la superficie du couvert forestier. Les parulines excluent les lignes sismiques recemment coupees de leur territoire en raison du manque de couvert de protection (couvert arbustif et en petits arbres) et des ressources alimentaires reduites attribuables aux grandes superficies de sol nu. La faible quantite de ressources alimentaires et les risques percus de predation semblent etre compenses une fois que la litiere forestiere (profondeur et etendue) et le couvert forestier ont ratteint les niveaux des massifs continus de forets. Toutefois, a mesure que la densite de conspecifiques augmente, les lignes sismiques servent vraisemblablement de reperes pour demarquer les limites des territoires, meme lorsque le couvert forestier et la litiere ont ete restaures. En modifiant la repartition spatiale des territoires, ce comportement peut amener une reduction de la densite de territoires pres des lignes sismiques. L’effet de repere dure plus longtemps que les effets imputables aux ressources alimentaires reduites et au risque percu de predation etant donne que la hauteur et la densite des arbres prennent plus de 40 ans a ratteindre les niveaux des massifs continus de forets. Les mesures destinees a attenuer l’impact des lignes sismiques devraient viser a restaurer le couvert forestier des que possible.