Weather and nest cavity characteristics influence fecundity in mountain chickadees.

Background: Examining direct and indirect effects on reproduction at multiple scales allows for a broad understanding of species' resilience to environmental change. We examine how the fecundity of the mountain chickadee (Poecile gambeli), a secondary cavity-nesting, insectivorous bird, varied in relation to factors at three scales: regional weather conditions, regional- and site-level food availability, site-level community dynamics, and nest-level cavity characteristics. We hypothesized that earlier laying dates and higher fecundity (clutch size, nest survival, brood size) would be associated with milder climatic conditions, increased food from insect outbreaks, lower densities of conspecifics and nest predators (red squirrel; Tamiasciurus hudsonicus), and safer (smaller, higher) cavities. Methods: We collected data on laying date, clutch size, brood size, nest fate (success/failure), and cavity characteristics from 513 mountain chickadee nests in tree cavities in temperate mixed coniferous-broadleaf forest in interior British Columbia, Canada, from 2000 to 2011. We surveyed annual abundances of mountain chickadees and squirrels using repeated point counts, and mountain pine beetle (Dendroctonus ponderosae) and lepidopteran defoliators by monitoring host trees and by using regional-scale aerial overview forest insect survey data. We used weather data (temperature, rain, snow) from a local Environment and Climate Change Canada weather station. We modeled laying date, clutch size, daily nest survival, and brood size as a function of predictors at regional-, site-, and nest-scales. Results and Conclusions: Measures of fecundity varied dramatically across years and spatial scales. At the regional (study-wide) scale, chickadees laid earlier and larger first clutches in warmer springs with minimal storms, and daily nest survival (DSR) increased with a 2-year lag in growing season temperature. Despite a doubling of mountain chickadee density that roughly accompanied the outbreaks of mountain pine beetle and lepidopteran defoliators, we found little evidence at the site scale that fecundity was influenced by insect availability, conspecific density, or predator density. At the nest scale, DSR and brood size increased with clutch size but DSR declined with nest cavity size indicating a positive reproductive effect of small-bodied cavity excavators. Double-brooding, rare in chickadees, occurred frequently in 2005 and 2007, coinciding with early breeding, high food availability from insect outbreaks, and warm spring temperatures with 0-1 spring storms. Our results support the idea that fecundity in secondary cavity-nesting species is impacted directly and indirectly by weather, and indirectly through changes in community dynamics (via cavity resource supply). We stress the importance of adopting holistic, community-level study frameworks to refine our understanding of fecundity in opportunistic and climate-sensitive species in future.

Bird protection treatments reduce bird-window collision risk at low-rise buildings within a Pacific coastal protected area.

Background: In North America, up to one billion birds are estimated to die annually due to collisions with glass. The transparent and reflective properties of glass present the illusion of a clear flight passage or continuous habitat. Approaches to reducing collision risk involve installing visual cues on glass that enable birds to perceive glass as a solid hazard at a sufficient distance to avoid it. Methods: We monitored for bird-window collisions between 2013 and 2018 to measure response to bird protection window treatments at two low-rise buildings at the Alaksen National Wildlife Area in Delta, British Columbia, Canada. After 2 years of collision monitoring in an untreated state, we retrofitted one building with Feather Friendly® circular adhesive markers applied in a grid pattern across all windows, enabling a field-based assessment of the relative reduction in collisions in the 2 years of monitoring following treatment. An adjacent building that had been constructed with a bird protective UV-treated glass called ORNILUX® Mikado, was monitored throughout the two study periods. Carcass persistence trials were conducted to evaluate the likelihood that carcasses were missed due to carcass removal between scheduled searches. Results and Conclusions: After accounting for differences in area of glass between the two buildings, year, and observer effects, our best-fit model for explaining collision risk included the building's treatment group, when compared to models that included building and season only. We found that the Feather Friendly® markers reduced collision risk at the retrofitted building by 95%. Collision incidence was also lower at the two monitored façades of the building with ORNILUX® glass compared to the building with untreated glass. Although more research is needed on the effectiveness of bird-protection products across a range of conditions, our results highlight the benefit of these products for reducing avian mortality due to collisions with glass.

Woodpeckers and other excavators maintain the diversity of cavity-nesting vertebrates.

Woodpeckers and other excavators create most of the holes used by secondary cavity nesters (SCNs) in North American temperate mixedwood forests, but the degree to which excavators release SCNs from nest-site limitation is debated. Our goal was to quantify how excavators maintain the diversity and abundance of secondary cavity nesters in a temperate forest through the creation of tree cavities. We examined the short- and long-term (legacy) effects of excavators (principally woodpeckers, but also red-breasted nuthatches and black-capped chickadees) on forest biodiversity using longitudinal monitoring data (1,732 nest cavities, 25 sites, 16 years) in British Columbia, Canada. Sites with higher densities of excavator nests had more cavities available, higher species richness of SCNs and higher nest density of SCNs, indicating the importance of a standing stock of cavities. Years with higher nesting densities of excavators were followed by years with higher SCN diversity, indicating that the creation of nesting opportunities through fresh excavation releases SCNs from community-wide nest-site limitation. We also show that excavators leave a 'legacy' of biodiversity (species richness and abundance) at a site by accumulating cavities at rates faster than they become unusable by decay or destruction. By quantifying site-level effects of cavity excavation on the SCN community, our study highlights the key role of excavators as ecosystem engineers that maintain forest wildlife biodiversity.

Si, dans la forêt mixte tempérée d'Amérique du Nord, les pics et autres excavateurs créent la plupart des cavités utilisées par les cavernicoles secondaires (SCN), la question de savoir s'ils augmentent la disponibilité des sites de nidification des SCN reste ouverte. Notre objectif était d'évaluer et quantifier l'impact qu'ont les excavateurs lorsqu'ils creusent des cavités dans les arbres, sur la diversité et l'abondance de cavernicoles secondaires dans une forêt mixte tempérée. Nous avons examiné les effets des excavateurs (principalement les pics, mais aussi la sittelle à poitrine rousse et la mésange à tête noire) à court et à long terme (survivance), sur la biodiversité de la forêt en Colombie-Britannique, au Canada, en utilisant des données longitudinales de surveillance (1,732 cavités ressource, 25 sites, 16 ans). Les sites à plus fortes densités de nids d'excavateurs avaient une plus grande abondance en cavités disponibles, une richesse en espèce SCN plus élevée, et une plus forte densité de nids de SCN, ce qui montre l'importance des arbres à cavités utilisables, vivants ou morts sur pied. Les années à plus fortes densités de nids d'excavateurs étaient suivies par des années à plus fortes diversités d'espèces SCN, ce qui signifie que la disponibilité de sites de nidification à partir de nouveaux creusements augmente le potentiel de nidification des espèces SCN pour l'ensemble de la communauté qui en dépend. Nous démontrons aussi que, sur un site donné, les excavateurs laissent une 'survivance' de biodiversité (richesse en espèce et abondance) en formant des cavités à un taux plus élevé que le taux avec lequel ces dernières deviennent inutilisables suite à leur décomposition ou destruction. En quantifiant les effets du creusement de cavités au niveau de chaque site par rapport à la communauté des SCN, notre étude met en évidence le rôle clé des excavateurs comme ingénieurs de l'écosystème favorisant la diversité de la faune forestière.

Nest boxes increase reproductive output for Tree Swallows in a forest grassland matrix in central British Columbia.

Secondary cavity-nesting birds depend on tree cavities for nesting and roosting, but many studies of these birds are conducted using nest boxes. Implementation of effective conservation strategies for cavity-nesting species such as nest-site supplementation requires careful comparisons of fecundity and other vital rates for birds using both natural and artificial nest site types. We compared breeding phenology, clutch and brood sizes, and fledging success of Tree Swallows (Tachycineta bicolor) nesting in tree cavities and nest boxes during 2001-2003 in British Columbia, Canada. Swallows using nest boxes initiated egg-laying and hatched young at approximately the same time as those in tree cavities (2 June, 23 June, respectively). Female Tree Swallows in boxes laid larger clutches (5.9 ± 0.9 eggs, N = 76) than those in tree cavities (4.2 ± 1.6 eggs, N = 67). The mean number of nestlings hatched was greater in nest boxes (5.2 ± 1.1 nestlings, N = 67) than in tree cavities (2.6 ± 2.0 nestlings, N = 58). Pairs in boxes were over twice as successful in producing fledglings (93.4%; 57 of 61 pairs fledged > 1 young) than those in tree cavities (35.8%; 19 of 53 pairs). Of those successful nests, pairs nesting in boxes fledged 5.1 ± 1.1 young (N = 57), whereas those in tree cavities fledged 3.5 ± 1.2 young (N = 18). Because cavities in nest boxes averaged 60% larger in volume and 1.8 cm wider internally than tree cavities, we suggest that increased reproductive output was correlated with boxes enabling a larger clutch size. In previous research, we found that Tree Swallows were a poor competitor with other cavity-nesting passerines for tree cavities. The addition of nest boxes may serve as an effective way to supplement local reproduction for secondary cavity-nesting bird populations by reducing competition for limited nest sites. This is especially true in regions where the availability of natural nesting sites is highly variable, and where species compete with many other cavity-nesting passerines using a similar ecological niche and nesting cavities.