Samuel Haché

Experimental evidence for an ideal free distribution in a breeding population of a territorial songbird

According to the ideal despotic distribution (IDD), dominant individuals gain a fitness advantage by acquiring territories that are of higher quality, thereby forcing other individuals into lower quality habitat. In contrast, the ideal free distribution (IFD) predicts that local density is a function of habitat quality, but that individuals achieve the same fitness in different habitat types as a result of density-dependent variation in territory size. Although the IFD represents an alternative, population dynamics of territorial species are generally expected to be driven by an IDD. We tested the predictions of IFD and IDD by monitoring the demographic response of the Ovenbird (Seiurus aurocapilla) to selection harvesting (30- 40% tree removal) during the first five years postharvest in five pairs of 25-ha study plots, each comprising a control (undisturbed) and a treatment (harvested plot). In the first year following harvesting, Ovenbird territory size increased in treatment plots relative to controls, whereas density, productivity per unit area, and the abundance of litter invertebrates decreased. Treatment effects declined consistently as stands regenerated, and most effects were no longer significant by the fifth year postharvest. However, there was no treatment effect on daily nest survival rate nor on per capita productivity. These results are consistent with the IFD, whereby similar per capita productivity is achieved across habitat types through density adjustments facilitated by changes in territory size. To our knowledge, this is the first study providing evidence for an IFD in a territorial bird species.

Age‐specific response of a migratory bird to an experimental alteration of its habitat

1. Recruitment, i.e. the influx of new breeding individuals into a population, is an important demographic parameter, especially in species with a short life span. Few studies have measured this parameter in solitary-breeding animal populations even though it may yield critical information on habitat suitability and functional connectivity. 2. Using a before-after, control-impact pairs (BACIP) experimental design, we measured: (i) the return rate and apparent survival rate of individually marked territorial males of a neotropical migrant bird species, the Ovenbird Seiurus aurocapilla Linnaeus and (ii) the age-specific recruitment rate. Study plots (n = 10) were paired: one was treated through single-tree selection harvesting (30-40% basal area removal) and the other acted as a control. We hypothesized that experienced males would out-compete inexperienced ones and tend to avoid settling in lower-quality, treated stands. 3. In the first year post-harvest, the mean density of territorial males was significantly lower in treated plots (-41%) than in controls and the difference remained relatively stable thereafter. This lower density mainly reflected a lower recruitment rate compared to controls (17.9 vs. 49.0% of males present), itself driven by a lower recruitment rate of experienced males (2.8 vs. 22.8%). Return rate was similar between controls and treated plots in the first year post-harvest (59 vs. 55%, respectively) but it decreased in treated plots during the second (-15.8% relative to controls) and third (-12.7%) year post-harvest. The trend was even stronger when considering only experienced males. The treatment was followed by a major expansion in mean territory size in treated plots (+49% relative to controls, 3rd year post-treatment). 4. Neither apparent survival rate nor recruitment rate varied as predicted. There was a strong year effect but no treatment effect on apparent survival rate, whereas male recruitment patterns were both year- and age-specific. Three years post-harvest, recruitment rate was sufficient to fill most territory vacancies in treated plots, due mainly to first-time breeders. 5. To our knowledge, this is the first study documenting the effects of experimental habitat alteration on recruitment rate in a songbird species using a BACI design. The response of this male subpopulation highlights the influence of recruitment on the density of open populations of solitary-nesting birds and age-specific patterns in the response of individuals to habitat alterations.

Tracking Natal Dispersal in a Coastal Population of a Migratory Songbird Using Feather Stable Isotope (δ2H, δ34S) Tracers

Adult birds tend to show high fidelity to their breeding territory or disperse over relatively short distances. Gene flow among avian populations is thus expected to occur primarily through natal dispersal. Although natal dispersal is a critical demographic process reflecting the area over which population dynamics take place, low recapture rates of birds breeding for the first time have limited our ability to reliably estimate dispersal rates and distances. Stable isotope approaches can elucidate origins of unmarked birds and so we generated year- and age-specific δ2H and δ34S feather isoscapes (ca. 180 000 km2) of coastal-breeding Ovenbirds (Seiurus aurocapilla) and used bivariate probability density functions to assign the likely natal areas of 35 males recruited as first-year breeders into a population located in northwestern New Brunswick, Canada. Most individuals (80–94% depending on the magnitude of an age correction factor used; i.e. 28–33 out of 35) were classified as residents (i.e. fledged within our study area) and estimated minimum dispersal distances of immigrants were between 40 and 240 km. Even when considering maximum dispersal distances, the likely origin of most first-year breeders was<200 km from our study area. Our method identified recruitment into our population from large geographic areas with relatively few samples whereas previous mark-recapture based methods have required orders of magnitude more individuals to describe dispersal at such geographic scales. Natal dispersal movements revealed here suggest the spatial scale over which many population processes are taking place and we suggest that conservation plans aiming to maintain populations of Ovenbirds and ecologically-similar species should consider management units within 100 or at most 200 km of target breeding populations.

Numerical Response of Breeding Birds Following Experimental Selection Harvesting in Northern Hardwood Forests

Silvicultural treatments have been shown to alter the composition of species assemblages in numerous taxa. However, the intensity and persistence of these effects have rarely been documented. We used a before-after, control-impact (BACI) paired design, i.e., five pairs of 25-ha study plots, 1-control and 1-treated plot, to quantify changes in the density of eight forest bird species in response to selection harvesting over six breeding seasons, one year preand five years postharvest. Focal species included mature forest associates, i.e., Northern Parula (Setophaga americana) and Black-throated Green Warbler (Setophaga virens), forest generalists, i.e., Yellow-bellied Sapsucker (Sphyrapicus varius) and Swainson’s Thrush (Catharus ustulatus), early-seral specialists, i.e., Mourning Warbler (Geothlypis philadelphia) and Chestnut-sided Warbler (Setophaga pensylvanica), species associated with shrubby forest gaps, i.e., Black-throated Blue Warbler (Setophaga caerulescens), and mid-seral species, i.e., American Redstart (Setophaga ruticilla). As predicted, we found a negative numerical response to the treatment in the Black-throated Green Warbler, no treatment effect in the Yellow-bellied Sapsucker, and a positive treatment effect in early-seral specialists. We only detected a year effect in the Northern Parula and the American Redstart. There was evidence for a positive treatment effect on the Swainson’s Thrush when the regeneration started to reach the pole stage, i.e., fifth year postharvest. These findings suggest that selection harvesting has the potential to maintain diverse avian assemblages while allowing sustainable management of timber supply, but future studies should determine whether mature-forest associates can sustain secondand third-entry selection harvest treatments. RESUME. Les traitements sylvicoles modifient la composition des assemblages d’especes de nombreux taxons. Toutefois, l’intensite et la duree des effets de ces traitements ont rarement ete evaluees. Notre etude visait a quantifier le changement observe dans la densite de huit especes d’oiseaux a la suite d’une coupe de jardinage. Pour ce faire, nous avons utilise un plan d’echantillonnage apparie du type BACI (pour before-after control-impact en anglais) consistant en cinq paires de sites (un temoin et l’autre experimental) de 25 ha chacun. Nos resultats portent sur six saisons de nidification, la premiere avant la coupe et les cinq suivantes, apres la coupe. Les especes etudiees comprenaient des specialistes de forets matures, c.-a-d. la Paruline a collier (Setophaga americana) et la Paruline a gorge noire (Setophaga virens), des especes forestieres generalistes, c.-a-d. le Pic macule (Sphyrapicus varius) et la Grive a dos olive (Catharus ustulatus), des specialistes de debut de succession, c.-a-d. la Paruline triste (Geothlypis philadelphia) et la Paruline a flancs marron (Setophaga pensylvanica), une specialiste des trouees forestieres, la Paruline bleue (Setophaga caerulescens), et une specialiste du stade intermediaire de succession, la Paruline flamboyante (Setophaga ruticilla). Tel qu’attendu, le traitement sylvicole a eu un effet negatif chez la Paruline a gorge noire, aucun effet chez le Pic macule et un effet positif chez les specialistes de debut de succession. Nous avons observe un effet de l’annee seulement chez les Parulines a collier et flamboyante. Un effet positif chez la Grive a dos olive a ete detecte lorsque la regeneration a atteint le stade de gaulis, c.-a-d. a la cinquieme annee apres la coupe. Nos resultats montrent que la coupe de jardinage a le potentiel de maintenir divers assemblages aviaires tout en permettant une recolte forestiere durable. Toutefois, les futures etudes devraient chercher a determiner si les specialistes des forets matures peuvent supporter une deuxieme ou une troisieme rotation de coupe de jardinage.

Postharvest regeneration, sciurid abundance, and postfledging survival and movements in an Ovenbird population

ABSTRACT Several studies have emphasized the importance of postfledging survival when estimating avian population growth rates, yet high variation exists in reported estimates. Mechanisms influencing postfledging survival also remain poorly understood. The influences of local habitat quality and landscape context on postfledging movements also remain largely undocumented. We measured daily postfledging survival and movements in Ovenbirds (Seiurus aurocapilla) in selection cut plots (30–40% basal area removal) and controls. Specifically, we tested predictions from the “concealment” hypothesis (higher survival/shorter movements with increased fledgling concealment), “body condition” hypothesis (higher survival/longer movements with increased body mass), and “predator abundance” hypothesis (higher survival/shorter movements when predator abundance is low) by monitoring fledgling survival (n = 55) and movements (n = 41) during the first 2 weeks postfledging. Fledglings were monitored over 2 breeding seasons in 5 pairs of experimental plots, 25 ha each (1 control and 1 treated plot per pair), located in mature hardwood stands. We found support for an effect of predator abundance on survival (i.e. effects of plot-level abundance of red squirrels and year). Models including habitat variables or body mass received weak support. A positive trend for effect of body mass on movement between successive locations was found but no evidence for an effect of predator abundance or habitat variables. These findings indicate that spatiotemporal variation in predator abundance was a key factor determining daily postfledging survival rate in this Ovenbird population; however, predator abundance did not influence movement rate, suggesting that fledgling Ovenbirds were unable to respond to predation risk.

Phylogeography of a migratory songbird across its Canadian breeding range: Implications for conservation units

Abstract The objectives of this study were to describe and evaluate potential drivers of genetic structure in Canadian breeding populations of the Ovenbird, Seiurus aurocapilla. We performed genetic analyses on feather samples of individuals from six study sites using nuclear microsatellites. We also assessed species identity and population genetic structure of quill mites (Acariformes, Syringophilidae). For male Ovenbirds breeding in three study sites, we collected light‐level geolocator data to document migratory paths and identify the wintering grounds. We also generated paleohindcast projections from bioclimatic models of Ovenbird distribution to identify potential refugia during the last glacial maximum (LGM, 21,000 years before present) as a factor explaining population genetic structure. Birds breeding in the Cypress Hills (Alberta/Saskatchewan) may be considered a distinct genetic unit, but there was no evidence for genetic differentiation among any other populations. We found relatively strong migratory connectivity in both western and eastern populations, but some evidence of mixing among populations on the wintering grounds. There was also little genetic variation among syringophilid mites from the different Ovenbird populations. These results are consistent with paleohindcast distribution predictions derived from two different global climate models indicating a continuous single LGM refugium, with the possibility of two refugia. Our results suggest that Ovenbird populations breeding in boreal and hemiboreal regions are panmictic, whereas the population breeding in Cypress Hills should be considered a distinct management unit.

Forestry and conspecifics influence Canada Warbler (Cardellina canadensis) habitat use and reproductive activity in boreal Alberta, Canada

ABSTRACT The Canada Warbler (Cardellina canadensis) is a threatened species in Canada due to an annual decline of ∼3% over the last 50 yr. Some studies suggest that Canada Warblers prefer old-growth forest and that forestry practices may reduce suitable habitat, while other research indicates that the species will also use harvested areas. Differences in scale between habitat use studies and behavioral phenomena such as conspecific attraction may explain this discrepancy. We examined how Canada Warblers responded to forestry and conspecifics in Alberta, Canada. We used point counts, burst sampling, and behavioral observations to determine how the density, home range placement (second-order habitat use), within-home-range space use (third-order habitat use), and probability of pairing and fledging young of male Canada Warblers were influenced by postharvest conditions (i.e. amount, age [≤ 30 yr postharvest], and retention of unharvested fragments) and conspecifics. Male density was 86% lower in postharvest than in unharvested stands. However, males were 16.6 times more likely to place their home ranges in postharvest stands within 100 m of unharvested stands than 300 m into harvested areas, and 3 times more likely to place their home ranges 100 m from conspecifics than 300 m away. Within-home-range space use was 1.1 times higher 50 m from conspecifics than 350 m away, and 2.6 times higher 300 m from an edge than 100 m away. Use of harvested areas did not affect reproductive activity, but the probability of pairing was 1.8 times higher for males in low-density (2 males per 17.3 ha) than in high-density areas (7 males per 17.3 ha). Our results suggest that Canada Warbler use of postharvest stands on the boreal breeding grounds is more heavily influenced by conspecifics than by postharvest conditions. Because Canada Warbler territories are clustered, conservation efforts should prioritize the retention of large tracts of unharvested forest near occupied breeding sites.

ENSO, Nest Predation Risk, Food Abundance, and Male Status Fail to Explain Annual Variations in the Apparent Survival Rate of a Migratory Songbird

Adult mortality can be a major driver of population decline in species whose productivity is relatively low. Yet, little is known about the factors influencing adult survival rates in migratory bird species, nor do we know much about the longer-term effects of habitat disturbance on the fitness of individuals. The Ovenbird (Seiurus aurocapilla) is one of the vertebrate species most sensitive to forest management, yet it is still common and widespread. We monitored the fate of 330 colour-banded Ovenbird males in four pairs of 25-ha plots during 9 successive breeding seasons. One plot of each pair was treated through selection harvesting (30–40% basal area removed) during the first winter. We tested the following hypotheses: (1) higher physiological costs in harvested plots as a result of lower food abundance will reduce apparent survival rate (ASR) relative to controls; (2) lower ASR following years with low nest survival and higher probability of renesting; (3) fluctuations in ASR reflecting El Niño Southern Oscillation (ENSO); and (4) higher ASR in returning males than in recruits (unbanded immigrants) owing to greater site familiarity in the former. We tested the relative importance of these hypotheses, or combinations thereof, by generating 23 models explaining variation in ASR. The year-dependent model received the most support, showing a 41% decrease in ASR from 2007 to 2014. The important year-to-year variation we observed in ASR (Σwi = 0.99) was not explained by variation in nest predation risk nor by ENSO. There was also little evidence for an effect of selection harvesting on ASR of Ovenbird males, despite a slight reduction in lifespan relative to males from control plots (2.7 vs 2.9 years). An avenue worth exploring to explain this intriguing pattern would be to determine whether conditions at migratory stopover sites or in the wintering area of our focal population have gradually worsened over the past decade.

Band-related Foot Loss Does Not Prevent Successful Return and Reproduction in the Ovenbird (Seiurus aurocapilla)

ABSTRACT In spite of recent developments in tracking technology, leg bands are still the main marking method in songbird population studies. Yet, band-related injury rates and the effects of such injuries on survival and reproductive success have rarely been documented in songbirds. Over a 9-year period, we banded 525 male Ovenbirds using a numbered aluminum band and three celluloid color bands. Of these, 322 individuals returned to our study area in at least one of the subsequent years, including four males (1.2%) missing a foot. In all cases, foot loss occurred 2–3 years after banding, suggesting indirect effects of bands rather than injuries sustained at the time of capture or banding. Among returning individuals, 91 were recaptured and only one had noticeable leg injuries that did not result in foot loss. Three of the four males missing a foot were able to fledge young, one of which produced young during two successive breeding seasons. The fact that injured males could hold territories overlapping their previous one and produce young suggests that they could forage efficiently. Although leg injuries may carry a cost over the longer term, two of the four injured males were re-sighted in our study area the year following the first observation of foot loss. Our results, along with those of other studies, suggest that the benefits of bird banding greatly outweigh the costs associated with potential injuries, at least in this ground-foraging forest songbird.

Within-Site Variation in Feather Stable Hydrogen Isotope (δ2Hf) Values of Boreal Songbirds: Implications for Assignment to Molt Origin.

Understanding bird migration and dispersal is important to inform full life-cycle conservation planning. Stable hydrogen isotope ratios from feathers (δ2Hf) can be linked to amount-weighted long-term, growing season precipitation δ2H (δ2Hp) surfaces to create δ2Hf isoscapes for assignment to molt origin. However, transfer functions linking δ2Hp with δ2Hf are influenced by physiological and environmental processes. A better understanding of the causes and consequences of variation in δ2Hf values among individuals and species will improve the predictive ability of geographic assignment tests. We tested for effects of species, land cover, forage substrate, nest substrate, diet composition, body mass, sex, and phylogenetic relatedness on δ2Hf from individuals at least two years old of 21 songbird species captured during the same breeding season at a site in northeastern Alberta, Canada. For four species, we also tested for a year × species interaction effect on δ2Hf. A model including species as single predictor received the most support (AIC weight = 0.74) in explaining variation in δ2Hf. A species-specific variance parameter was part of all best-ranked models, suggesting variation in δ2Hf was not consistent among species. The second best-ranked model included a forage substrate × diet interaction term (AIC weight = 0.16). There was a significant year × species interaction effect on δ2Hf suggesting that interspecific differences in δ2Hf can differ among years. Our results suggest that within- and among-year interspecific variation in δ2Hf is the most important source of variance typically not being explicitly quantified in geographic assignment tests using non-specific transfer functions to convert δ2Hp into δ2Hf. However, this source of variation is consistent with the range of variation from the transfer functions most commonly being propagated in assignment tests of geographic origins for passerines breeding in North America.