Jacques Ibarzabal

Playbacks of mobbing calls of Black-capped Chickadees as a method to estimate reproductive activity of forest birds

Abstract Community-level indices of reproductive success are useful for measuring or monitoring demographic effects of habitat alteration on birds. We present a time-efficient method to estimate the relative reproductive activity of the forest songbird community. A recording of mobbing calls of Black-capped Chickadees (Poecile atricapillus) was broadcast at pre-selected stations during the breeding season. These calls attracted individuals of many bird species present in the vicinity, allowing visual detection of reproductive activity (e.g., adults carrying food or presumed pairs). In mature deciduous forests of northern New Brunswick, 50 bird species responded to the playbacks. Playbacks significantly increased the probability of visual observations of birds compared to silent observations conducted before broadcasting mobbing calls. In coniferous forests of central Québec, playbacks attracted 24 species and also provided a significantly greater opportunity to make visual observations of individual birds. In New Brunswick, mobbing playbacks facilitated more observations of reproductive evidence relative to point counts. Observation periods were brief and a 306-ha plot (1.75 × 1.75 km, 64 points spaced 250 m apart) could be surveyed by foot in less than 32 observer-hours. The proportion of individuals of a given species showing evidence of reproductive activity was used as an index of reproductive success. Black-throated Blue Warblers (Dendroica caerulescens) and Ovenbirds (Seiurus aurocapillus) had a reproductive index consistent with their true nesting success as derived from intensive nest monitoring on the same plots.

Effects of habitat characteristics and interspecific interactions on co-occurrence patterns of saproxylic beetles breeding in tree boles after forest fire: null model analyses

It is often suggested that habitat attributes and interspecific interactions can cause non-random species co-occurrence patterns, but quantifying their contributions can be difficult. Null models that systematically exclude and include habitat effects can give information on the contribution of these factors to community assembly. In the boreal forest, saproxylic beetles are known to be attracted to recently burned forests where they breed in dead and dying trees. We examined whether species co-occurrences of saproxylic beetles that develop in, and emerge from, boles of recently burned trees show non-random patterns. We also estimated the extent to which both the post-fire habitat attributes and interspecific interactions among beetles contribute to such patterns. We sampled tree boles encompassing key attributes (tree species, tree size/dbh and burn severity) that are thought to characterize species–habitat associations of saproxylic beetles, a proposition that we tested using indicator species analysis. Two null models with no habitat constraints (“unconstrained”) indicated that a total of 29.4% of the species pairs tested had significant co-occurrence patterns. Habitat-constrained null models indicated that most of the detected species aggregations (72%) and segregations (59%) can be explained by shared and distinct species–habitat relationships, respectively. The assembly pattern was also driven by interspecific interactions, of which some were modulated by habitat; for example, predator and prey species tended to co-occur in large-sized trees (a proxy of available bark/wood food resource primarily for the prey). In addition, some species segregation suggesting antagonistic, competitive, or prey–predator interactions were evident after accounting for the species’ affinities for the same tree species. Overall, our results suggest that an intimate link between habitat and interspecific interactions can have important roles for community assembly of saproxylic assemblages even following disturbance by fire. We also show that a systematic application of null models can offer insight into the mechanisms behind the assembly of ecological communities.

Saproxylic Beetles in Disturbed Boreal Forests: Temporal Dynamics, Habitat Associations, and Community Structure

Abstract: Early postfire habitats harbour numerous saproxylic species. Some are opportunistic feeders, while others are closely associated with burned forests. This distinction is important for developing sound postfire forest management aimed at conserving biodiversity, as concerns should be mostly directed towards burn-associated saproxylic beetles rather than opportunistic species. Here, we examine species-habitat associations, temporal dynamics, and community structure of saproxylic beetles in black spruce and jack pine stands disturbed by wildfire and by a “non-fire” disturbance generated by girdling trees to mimic the small-scale gap dynamics characterizing old-growth boreal forests in Canada. We used flightinterception traps and reared logs to compare abundance, species richness, and species composition of saproxylic beetles among treatments. We found that over 30% of saproxylic beetles had an affinity with jack pine or black spruce affected by either fire or girdling. Assemblages consistently differed between disturbance types over the 3 y of the study. We found that successional changes in species composition were more pronounced in burned sites than those with the girdling treatment, which indicates that the contribution of fire-generated habitats to regional diversity increases over time. While postfire forests are notable for their early-colonizing saproxylic species, our results show that they can also have substantial value for supporting mid-successional species such as Acmaeops pratensis, which is already on European red lists. This forewarns us about long-term negative consequences that postfire salvage logging could have for certain species.

A NEST PREDATOR'S VIEW OF A MANAGED FOREST: GRAY JAY (PERISOREUS CANADENSIS) MOVEMENT PATTERNS IN RESPONSE TO FOREST EDGES

Abstract High nest-predation risk is often associated with forest edges. Most nest predators in boreal coniferous forests of North America are forest specialists living in mature stands. Nest predators have been studied mainly through use of artificial nests; knowledge of their behavior remains limited. We used radiotelemetry to examine movement patterns, relative to forest edge, of a forest nest predator, the Gray Jay (Perisoreus canadensis), in boreal coniferous forest. Each of 11 family groups of Gray Jays monitored in early summer exhibited a marked association with forest edges. Jays were found within 30 m of the forest edges more often than expected from random use of mature forest. Furthermore, jays traveled more slowly near forest edges than in the forest interior. Because forest edges apparently represent prime foraging habitat for Gray Jays, narrow forest strips left by logging could act as ecological traps for mature-stand songbirds before stands regenerate in adjacent clearcuts.

Habitat Requirements of Breeding Black-Backed Woodpeckers ( Picoides arcticus ) in Managed, Unburned Boreal Forest

We investigated home-range characteristics and habitat selection by Black-backed Woodpeckers (Picoides arcticus) in an unburned, boreal forest landscape managed by mosaic harvesting in Quebec, Canada. Habitat selection by this species was specifically examined to determine home-range establishment and foraging activities. We hypothesized that Black-backed Woodpeckers would respond to harvesting by adjusting their home-range size as a function of the amount of dead wood available. Twenty-two birds were tracked using radiotelemetry, and reliable estimates of home-range size were obtained for seven breeding individuals (six males and one female). The average home-range size was 151.5 +/- 18.8 ha (range: 100.4-256.4 ha). Our results indicate that this species establishes home ranges in areas where both open and forested habitats are available. However, during foraging activities, individuals preferentially selected areas dominated by old coniferous stands. The study also showed that the spatial distribution of preferred foraging habitat patches influenced space use, with home-range area increasing with the median distance between old coniferous habitat patches available within the landscape. Finally, these data show that Black-backed Woodpeckers may successfully breed in an unburned forest with at least 35m3 • ha-1 of dead wood, of which 42% (15m3• ha-1) is represented by dead wood at the early decay stage. Nous avons etudie les caracteristiques du domaine vital et la selection de l’habitat chez le Pic a dos noir (Picoides arcticus) en foret boreale non brulee et amenagee par coupes en mosaique, au Quebec (Canada). La selection de l’habitat a ete tout particulierement examinee afin de determiner le domaine vital et les activites liees a l’alimentation chez cette espece. Nous avons emis l’hypothese selon laquelle le Pic a dos noir reagirait a la recolte de bois en modifiant la taille de son domaine vital selon la quantite de bois mort accessible. Vingt-deux oiseaux ont ete suivis a l’aide de la telemetrie et des estimations fiables de la taille du domaine vital ont ete obtenues pour sept individus nicheurs (six mâles et une femelle). La taille moyenne du domaine vital a ete evaluee a 151,5 ± 18,8 ha (etendue : 100,4–256,4 ha). Nos resultats indiquent que cette espece etablit son domaine vital la ou des milieux ouverts et des milieux forestiers sont accessibles. Toutefois, au moment de s’alimenter, les individus selectionnent preferablement les endroits ou dominent les peuplements de vieux coniferes. Les travaux ont egalement montre que la repartition spatiale des ilots d’habitat preferes pour l’alimentation du pic influence l’utilisation de l’espace : la taille du domaine vital augmente en fonction de la distance mediane entre les ilots de vieux coniferes accessibles dans le paysage. Enfin, les resultats indiquent que le Pic a dos noir peut nicher avec succes en foret non brulee s’il y a un volume de bois mort d’au moins 35 m3 • ha-1, dont 42 % (15 m3 • ha-1) est en debut de decomposition.

Age-Dependent Response of Migrant and Resident Aegolius Owl Species to Small Rodent Population Fluctuations in the Eastern Canadian Boreal Forest

ABSTRACT We investigated the relationship between late summer abundance of small rodents and fall migrant abundance of two nocturnal avian predators, the Boreal Owl (Aegolius funereus) and the Northern Saw-whet Owl (A. acadicus), during their fall movement/migration. In the eastern Canadian boreal forest, Boreal Owls are considered resident (with irruptive movements to the south thought to occur during periods of low prey availability), and Northern Saw-whet Owls migratory. Data on late summer abundance of small rodents collected between 1995 and 2004 were used to develop an index of prey availability. Data on the number and age of irrupting/migrating owls were collected between 1996–2004 (mid-September to late October) using audiolures and mist nets. Our study revealed strong evidence of (1) a negative relationship between the abundance of small rodents and movement of Boreal Owls and (2) a positive relationship between the abundance of small rodents and the number of migrating juveniles and second year Northern Saw-whet Owls. In the latter case, it suggests that prey availability can strongly influence breeding success of this species, which is at the northern limit of its breeding range.

A Comparison between Nocturnal Aural Counts of Passerines and Radar Reflectivity from a Canadian Weather Surveillance Radar

ABSTRACT. 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 NEXRADs coverage farther north by hundreds of kilometers, thereby increasing our understanding of how birds use the North American landscapes during migration.

Differential Effects of Post-Fire Habitat Legacies on Beta Diversity Patterns of Saproxylic Beetles in the Boreal Forest

Abstract: Fire-generated mosaics of habitat legacies such as dead and dying trees are key structural components in boreal forest ecosystems that support diverse saproxylic beetles. Our study sought to elucidate the spatial pattern of community composition (beta diversity) of saproxylic beetles along gradients of post-fire habitat legacies (tree species composition, tree size [dbh], and burn severities) and geographical distance. For 2 y, we reared saproxylic beetles from 360 logs retrieved from 72 sites in burned forests. Tests were performed to explain the overall beta diversity (&bgr;sor) by partitioning it into its 2 components: the “species spatial turnover” due to species replacement (&bgr;sim) and the “richness-driven” beta diversity due to species richness differences (&bgr;rich)- Variations in tree species, tree size, and burn severity had significant effects on overall beta diversity (&bgr;sor) of saproxylic beetles; these effects varied according to the differential influence of these factors on the 2 distinct components of beta diversity. Tree composition had notable effects on species spatial turnover (&bgr;sim), for which saproxylic species composition differed between jack pine and black spruce, and it was more variable between jack pine sites than between black spruce sites. On the other hand, variation in tree size was primarily responsible for the richness-driven beta diversity component (&bgr;rich), which was highest between the smallest and largest dbh groups and lowest between largest and mid-sized trees. Similarly, richness-driven composition differed significantly across severity gradients and was highest across low to high severity and lowest between low-severity stands. Broader geographical distance per se did not affect compositional patterns of saproxylic beetles, yet the landscape context could have some effect. These results could have crucial implications for post-fire management, which also aims to efficiently conserve saproxylic beetles. The significant spatial turnover in saproxylic composition between black spruce and jack pine and the underlying host-tree specificity suggest that a mosaic of both tree species should be maintained in the landscape. The richness-driven beta diversity pattern along the tree size and severity gradients implies that it may be necessary to prioritize the most species-rich classes, such as larger trees with lower severity burns, but with qualifications to cater also for species displaying idiosyncratic distributions.

Towards a Better Understanding of Beta Diversity: Deconstructing Composition Patterns of Saproxylic Beetles Breeding in Recently Burnt Boreal Forest

Biodiversity patterns vary across space and time, and this variation is thought to be driven by several ecological/biogeographical processes that act upon species distributions and leave their imprint at various spatial and temporal scales (Huston, 1994; Ricklefs, 2004). The regional or geographical (gamma diversity) diversity patterns, in addition to local diversity (alpha diversity), are consequent upon the extent of “spatial” variation in species composition among sites (beta diversity) (Whittaker, 1960; 1972). Arrays of ecological hypotheses have been proposed as determinants of beta diversity patterns. It can arise from variation in environmental/habitat heterogeneity among sites, spatial constraints, disturbance regimes, and corresponding species-level variations in life history traits (e.g., dispersal, niche-breadth) (Harrison et al., 1992; Nekola & White, 1999; Chase, 2007; Veech & Crist, 2007; Baselga, 2008) as well as neutral and/or stochastic processes (Hubbell, 2001; Chase, 2010). Nevertheless, beta diversity patterns and the mechanisms by which ensembles of local communities maintain their variations and, consequently, influence diversity at regional scale remains a central challenge in ecological and conservation studies (Wilson & Shmida, 1984; Veech & Crist, 2007; Baselga, 2010; Chase, 2010; Tuomisto, 2010; Anderson et al., 2011). Despite its apparent conceptual simplicity, the empirical assessment of beta diversity has been mired with extensive debates over a perplexing array of indices, analytical approaches, or scales of analysis (Wilson & Shmida, 1984; Lande, 1996; Loreau, 2000; Koleff et al., 2003; Tuomisto & Ruokolainen, 2006; Legendre et al., 2008; Veech & Crist, 2010; for a detailed outline of the issues, see recent review by Anderson et al., 2011). One of the most fundamental and recurrent challenges in beta diversity studies has been distinguishing and quantifying the pure “spatial” turnover component of beta diversity from that caused by variation in species richness between local communities (Wilson & Shmida, 1984; Koleff et al., 2003; Veech & Crist,

Host Tree Species and Burn Treatment as Determinants of Preference and Suitability for Monochamus scutellatus scutellatus (Coleoptera: Cerambycidae)

ABSTRACT After fire, the whitespotted sawyer, Monochamus scutellatus scutellatus (Say) (Coleoptera: Cerambycidae), is considered one of the most damaging xylophagous insects by forest industries in the eastern boreal forest of North America. Although this species is often considered opportunistic because it dwells on various stressed host trees, it can be found in very high abundance after forest fire and, consequently, it has been suspected of being a pyrophilous species or fireassociated species. The aim of this study was first to determine whether the whitespotted sawyer lays eggs preferentially on burned rather than unburned hosts, and second, to determine its preference between black spruce (Picea mariana [Mill] B.S.P.) and jack pine (Pinus banksiana Lamb.) for oviposition. Host suitability also was estimated to determine if whitespotted sawyer females make optimal choices to maximize offspring development. To determine host suitability, we used the abundance distribution of larval instars as a proxy of larval development quickness and we compared weight and head-capsule width of larvae of different larval instars as measures of insect growth in each type of log. Based on the frequency of oviposition behavior, females showed no preference for either burned or unburned black spruce logs, and both were equally suitable for larval development. Furthermore, females laid more eggs on black spruce than on jack pine, but host suitability was not statistically affected. Nevertheless, larvae had mostly reached the fourth instar on black spruce, whereas those on jack pine were mostly at the third instar, suggesting faster development on black spruce.