Dawn singing in Brown Creeper (Certhia americana)

The dawn chorus of birds is an impressive display in which many individuals of a variety of species sing concurrently before sunrise. Brown Creeper (Certhia americana) is a small passerine bird that has not been well studied and is thought not to sing during the dawn chorus. Here, we used automated recordings to analyze Brown Creeper singing during the 2015–2017 breeding seasons from April through August in order to identify patterns in the timing and quantity of singing. We found that Brown Creepers did sing before sunrise, most often between April and early June and then more sporadically through mid July. We did not find any seasonal changes in song rates before sunrise, but we did find non-linear seasonal trends in both the timing and total duration of dawn singing bouts. Dawn choruses began earlier and lasted longer from April through mid June after which they began later and became shorter. Our results highlight the benefit of using automated recording techniques to study natural history of difficult to study species and add to our understanding of Brown Creeper natural history.

Estimating fecundity and density dependence from mark-recapture data for making population projections

Forecasting changes in size and distributions of populations is at the forefront of ecological sciences in the 21st century. Such forecasts require robust estimators of fecundity, survival and density-dependence. While survival estimation is the main focus of mark-recapture modelling, fecundity and density dependence are rarely the subject of these models. Here, we demonstrate that these parameters can be simultaneously estimated in a Bayesian framework using only robust design mark-recapture data. Using simulated capture histories, we show that this framework (which we named CJS-pop) can estimate vital rates and their density dependence with little bias. When CJS-pop is applied to capture history data from Brown Creeper (Certhia americana), it provides estimates of fecundity that is expected from the breeding biology of this species. Finally, we illustrate that density dependence, even when estimated with uncertainty in the CJS-pop framework, regularizes population dynamics and reduces the frequent population extinctions and explosions observed under density-independent models. While CJS-pop as a whole is a useful addition to the current mark-recapture modelling toolbox, we argue that the independent components of this framework in estimating fecundity and density dependence can be integrated to other CJS frameworks, potentially creating models capable of population projections.

Nest site characteristics of cavity-nesting birds on a small island, in Haida Gwaii, British Columbia, Canada

Many studies of cavity-nesting birds in North America are conducted in large continental forests and much less is known about them in island ecosystems. We describe a 29-year study of tree species, nest site characteristics, and fledge dates of cavity-nesting birds on a small island in Haida Gwaii, British Columbia (BC). Seven cavity-nesting bird species were documented on East Limestone Island and 463 nests were found in 173 different trees. Nest trees were significantly taller and had a greater diameter than a random sample of snags. Tree height did not differ among bird species but diameter at breast height was larger for trees used by Brown Creeper (Certhia americana) than for other species. Cavity-nesters selected tree decay classes 2–7 (all dead/near dead [snags]), with 85% in decay class 4 (35%) or 5 (50%), similar to the random snag sample (class 4, 32%; class 5, 42%). Cavity height ranged from 2.6 to 44.9 m and for all species, except Brown Creeper, the mean nest height was >60% of the mean tree height. Nest heights were generally greater than observed elsewhere in BC. Nest cavity orientation was random except for Red-breasted Sapsuckers (Sphyrapicus ruber), for which only 13% of the cavity entrances faced southeast. Median fledging dates ranged from 7 June (Chestnut-backed Chickadee [Poecile rufescens]) to 28 June (Northern Flicker [Colaptes auratus]). Estimated median dates of clutch completion were similar for all species. Our results show that large snags provide habitat for a high diversity of cavity-nesting birds on Haida Gwaii.

Brown Creeper (Certhia americana) demographic response to hardwood forests managed under the selection system

The Brown Creeper (Certhia americana Bonaparte, 1838) has been identified as one of the most sensitive passerines to partial forest harvest in North America. The effect of selection logging on Brown Creeper density, nest timing, nest survival, and nest and foraging site selection was examined in five silviculture treatments (intensive group selection, typical group selection, old single-tree selection, recent single-tree selection, and control forests) of Algonquin Provincial Park, Canada. As Brown Creeper nests under the bark of large, decaying trees, we hypothesized that Brown Creeper density, timing of breeding, nest survival, and nest and foraging site selection would be negatively affected by silviculture through the removal of large, decaying trees as part of providing safe conditions for loggers. We monitored 101 nests of Brown Creeper during the 2010 and 2011 breeding seasons, mapped territories to estimate density, and conducted foraging surveys. Brown Creeper density was reduced by about 42% in logged stands compared with control stands. Despite that, silviculture did not significantly alter timing of breeding or nest survival. However, the loss of large trees through partial harvesting meant that Brown Creeper nested closer to adjacent, small forested wetlands and often in balsam fir (Abies balsamea (L.) Mill.) in treated stands. In control stands, Brown Creeper nested further from forested wetlands, disproportionately in greater numbers in upland hardwoods, and preferentially in the bark of snags of yellow birch (Betula alleghaniensis Britton). The change in the species of tree used for nesting and the general forest type as a result of logging also resulted in consequences for the selection of foraging substrates. To maintain higher densities of Brown Creeper in logged stands in Algonquin Park, we recommend retaining larger diameter yellow birch, both snags and live trees, preferably within strategically located uncut reserves based on habitat supply planning, that maintains patches roughly the size of Brown Creeper territories (10 ha).

A genomic investigation of the putative contact zone between divergent Brown Creeper (Certhia americana) lineages: chromosomal patterns of genetic differentiation

Sky islands, or montane forest separated by different lowland habitats, are highly fragmented regions that potentially limit gene flow between isolated populations. In the sky islands of the Madrean Archipelago (Arizona, USA), various taxa display different phylogeographic patterns, from unrestricted gene flow among sky islands to complex patterns with multiple distinct lineages. Using genomic-level approaches allows the investigation of differential patterns of gene flow, selection, and genetic differentiation among chromosomes and specific genomic regions between sky island populations. Here, we used thousands of SNPs to investigate the putative contact zone of divergent Brown Creeper (Certhia americana) lineages in the Madrean Archipelago sky islands. We found the two lineages to be completely allopatric (during the breeding season) with a lack of hybridization and gene flow between lineages and no genetic structure among sky islands within lineages. Additionally, the two lineages inhabit different climatic and ecosystem conditions and have many local primary song dialects in the southern Arizona mountain ranges. We identified a positive relationship between genetic differentiation and chromosome size, but the sex chromosome (Z) was not found to be an outlier. Differential patterns of genetic differentiation per chromosome may be explained by genetic drift—possibly in conjunction with non-random mating and non-random gene flow—due to variance in recombination rates among chromosomes.

Does postharvest silviculture improve convergence of avian communities in managed and old-growth boreal forests?

Habitat change following forest management may reduce biodiversity in boreal forests, as it has done globally in many forest types. Postharvest silviculture (PHS) is implemented to improve the yield of commercial tree species and has been applied to large areas of boreal forests. PHS may also influence animal communities and so we assessed songbird responses to these treatments in stands 20–52 years old in Ontario, Canada. We expected that several old-forest species would respond positively to PHS, that avian assemblages in treated forests would be distinct from those in untreated managed forests regardless of age, and that assemblages in our oldest treated stands would begin to converge with those of mature unmanaged forests. PHS stands had higher conifer density than naturally regenerating managed stands. The avian assemblage differed between treated and untreated stands at 20–30 years but not at 31–52 years. Convergence with old-forest assemblages was incomplete at 31–52 years after harvesting, although abundances of seven of 13 old-forest species did not differ from those in unmanaged forests. Of 10 old-forest species with competitive models, only Bay-breasted Warbler (Setophaga castanea (Wilson, 1810)) responded positively to PHS at the stand level, whereas two species responded positively at the landscape scale. Brown Creeper (Certhia americana Bonaparte, 1838), Boreal Chickadee (Poecile hudsonicus Forster, 1772), and Blackburnian Warbler (Setophaga fusca (Müller, 1776)) were absent from most managed stands and so require specific attention in planning for forest management, including retention of old-forest and delaying harvest of second-growth stands to ensure their occurrence and persistence.