Canadian Journal of Zoology

Whether regulation of protein synthesis, autophagy, and regeneration are involved in slow/fast muscles in two disuse models (hindlimb unloading Sprague-Dawley rats (Rattus norvegicus domestica (Berkenhout, 1769))) (HLU) and hibernating ground squirrels (Spermophilus dauricus Brandt, 1843 (HIB)) is still unclear. Our results showed (1) fiber cross-sectional area was reduced in soleus (SOL) and extensor digitorum longus (EDL) of HLU whereas no change in HIB. The satellite cells/fiber was reduced and myonuclei/fiber was increased in SOL of HLU, while the percentage of satellite cells was significantly reduced in EDL of HIB. (2) Protein levels of phosphorylated- (P-)Akt, mTORC1, P-mTORC1, and P-S6K1 were reduced in SOL of HLU, whereas phosphorylated S6K1 was increased only in EDL of HIB. (3) Myostatin decreased in EDL of HLU but decreased in SOL of HIB. (4) Beclin1 increased in EDL of HLU and in SOL of HIB. (5) The activity of cathepsin L increased in SOL of HIB. (6) Collagen III increased in both SOL and EDL of HLU, but myogenin and collagen III increased in SOL, and collagen III was reduced in EDL of HIB. Taken together, Akt-mTORC1, Beclin1, and myogenin signaling showed muscle-specific responses in slow-twitch versus fast-twitch muscles, which may contribute to disuse atrophy in non-hibernators and anti-atrophy in hibernators.

Fishing technologies often exploit the visual sensitivity of target species to alter their behaviours. Atlantic cod (Gadus morhua Linnaeus, 1758) are an economically important species, commonly targeted by fisheries in the North Atlantic, yet the behaviour of adult Atlantic cod in reaction to the simultaneous presentation of various light stimuli has not been assessed in an isolated setting to determine if there is a preference for certain light qualities. To assess the influence that artificial light may have on the behaviour of Atlantic cod, we investigated the movement of wild-caught cod in a laboratory setting with green, blue, and white light with a blank control presented in paired choice tests. We predicted that green light would have the greatest influence on cod behaviour and that they would preferentially spend more time in proximity to that light condition. The findings show that cod behaved consistently across trials and across experimental sessions, and that the right side of the arena was preferred regardless of the colours of light presented. These findings indicate that cod do not prefer to spend more time in proximity to certain colours of light in an artificial environment, which has direct implications for animal husbandry, fisheries research, and behavioural ecology.

White Stork (WS) (Ciconia ciconia (Linnaeus, 1758)) ranks among the most common breeding birds in many Mediterranean cities, underscoring the importance of studying nest densities, particularly when populations are increasing. In this study, conducted in Rabat (Morocco), we aimed to investigate the effects of coloniality, landscape composition, and space to identify the best predictors of variation in the number of WS nests per nest support using generalized linear mixed models. The results revealed significant interactions between the type of support (trees vs. pylons) and normalized difference vegetation index (NDVI) as well as between the support type and the distance to the nearest support occupied by WS and Cattle Egret (CE) (Bubulcus ibis (Linnaeus, 1758)) nests. A high number of nests are associated with an NDVI increase around pylons, while such an effect is insignificant around trees. In contrast, a high number of WS nests are noted close to supports occupied by both WS and CE nests, whereas in pylons, this number is recorded far away from them. The implementation of a scientific monitoring system is crucial for determining, at a defined time step, the direction and strength of relations between WS and CE populations in Rabat.

During fish larvae development functional, morphological, and physiological adaptations are key in larval survival strategies and can determine mortality bottlenecks. For many fish groups such as needlefish, which play crucial roles in marine food webs, studies on early life stages are almost lacking. Herein, the development, with focus on the postcranial skeleton, of the garfish Belone belone (Linnaeus, 1761) is described and a staging system is introduced. Ten larval and juvenile life stages are proposed in three main phases: yolk sac, larval, and juvenile development. During the yolk sac phase the garfish deplete their yolk reservoirs and finish the development of their unpaired fins. During the larval period the lower jaw elongates and the needlenose stage is reached. In the juvenile phase, the upper jaw elongates until both jaws are almost equally long. Since B. belone larvae develop much of their postcranial skeleton in the late embryonic and yolk sac phases they might not experience a severe bottleneck in this early stage such as many other marine fish species. Therefore, young garfish could be more resilient to environmental changes.

Synthetic pheromones formulated for Acossus centerensis Lintner, 1877 led to the discovery of a new taxonomically cryptic species, Acossus boreocryptus Schmidt & Jaeger sp. nov. Adult males were active only during the daytime, exceptional among cossid moths, and the first documented case of diurnality in New World Cossidae. Males were attracted to lures baited with (E,E) 3,5-tetradecadienyl acetate (EE-TDDA). The larval host plant of A. boreocryptus is trembling aspen, Populus tremuloides Michx., but the immature stages remain undescribed. Acossus boreocryptus is the smallest species in the genus, distinguished from its sister species A. centerensis by adult morphology, mtDNA barcode, male diurnal activity, and seasonal phenology.

Currently, natural forests face significant loss of vegetation cover linked to habitat loss due to urban expansion. Therefore, we investigated the effects of changes in different land uses and land cover at the landscape scale resulting from the urbanization process on the functional traits of the body of scorpions in the Brazilian Atlantic Forest. In 10 forest fragments in Paulista, Pernambuco, we observed that forest cover had a statistically significant negative relationship with the average functional body traits of the scorpion assemblage. Distinct functional body traits were associated with the conditions of the surrounding landscape. Forest units with lower forest cover harbored species with higher average functional body traits, indicating adaptation to the urban scenario. Conversely, in areas with greater forest cover, species with smaller functional body traits predominated, suggesting habitat sensitivity and dependence on less disturbed environments. Our results indicate that scorpions may be indicators of changes in functional body traits due to land use change. These findings highlight significant implications for biodiversity conservation in the Atlantic Forest in the face of urban expansion, emphasizing the role of scorpions as key indicators of changes in functional body traits in response to the altered landscape.

Aggregation behavior is pervasive across a broad range of animals and the outcome of this behaviour has both risks and rewards. Large aggregations of animals are a distinctive characteristic of Migratory Caribou (Rangifer tarandus Linnaeus, 1758), primarily in response to the environment factors such as predation, although caribou may also aggregate during high summer temperatures, likely in an effort to mitigate parasitic biting flies. To see if caribou in the Cape Churchill Caribou Herd of the Eastern Migratory caribou (Rangifer tarandus groenlandicus Borowski, 1780) Designatible Unit, also displayed aggregation behavior in relation to warmer summer temperatures, we collected trail camera photos with associated temperature readings during the summer period (May to September) from 2017 to 2020 in their summer range in Wapusk National Park, Manitoba, Canada. We found that summer caribou aggregation size was positively associated with ambient temperature, with aggregations increasing in size as temperature increased. The mechanism behind this behaviour should be investigated, as we predict more frequent and large caribou aggregations as summer temperatures continue to warm.

Understanding and predicting species range shifts is crucial for conservation amid global warming. This study analyzes life-history traits of four seal species (ringed (Pusa hispida (Schreber, 1775)), bearded (Erignathus barbatus (Erxleben, 1777)), harp (Pagophilus groenlandicus (Erxleben, 1777)), and harbour (Phoca vitulina Linnaeus, 1758) seals) in the Canadian Arctic using data from Inuit subsistence harvests. Bearded seals are largest, followed by harp seals, harbour seals, and ringed seals. Seasonal blubber depth patterns show minimal variation in bearded seals, whereas harbour and ringed seals accumulate fat in open-water seasons and use it during ice-covered seasons. Endemic Arctic seals (ringed and bearded) exhibit greater longevity and determinate body growth, reaching maximum size by 5 years, while harbour and harp seals grow indeterminately, physically maturing around 10–15 years. Age of maturation varies, with ringed and harbour seals being more sensitive to environmental fluctuations. Most bearded seals reproduce successfully each year, while ringed seals exhibit more variability in their annual reproductive success. Analysis of isoprenoid lipids in liver tissue indicates that ringed and bearded seals rely on ice-algal production, whereas harp and harbour seals depend on open-water phytoplankton production. Bearded seals appear more specialized and potentially face less competition, while harp seals may adapt better to changing habitats. Despite expected range shifts to higher latitudes, all species exhibit trade-offs, complicating predictions for the evolving Arctic environment.

Morphological abnormalities in amphibians are commonly associated with anthropogenic activity, although little baseline information on the prevalence of abnormalities in uncontaminated environments exist. Here, we leverage a 12-year study of spotted salamanders (Ambystoma maculatum Shaw, 1802) in an uncontaminated ecosystem in Algonquin Provincial Park, Canada, to estimate abnormality rates and explore how abnormalities affect fitness-related traits. Annual abnormality rates estimated from drift fence data, ranged from 4.3% to 5.8% of individuals sampled. Abnormality rates from aquatic trapping between 2008–2019 varied from 1.2% to 16.7%, where temporal increases in abnormality rate were observed. We also performed a targeted but systematic literature survey and found that Caudata exhibited a slightly higher abnormality prevalence than Anura, and that the baseline frequency of abnormalities described at our drift fence site is slightly lower than rates reported in the literature (8.1%, 95% CI, 4.76–13.3%). Salamanders with abnormalities exhibited a slightly, but not significantly, higher body condition and a significantly earlier arrival date at the breeding site, both of which are traits typically associated with high-fitness individuals. Our study suggests that abnormalities have detectable phenotypic consequences and underlines the need for temporal sampling efforts to provide ranges of baseline abnormality rates, rather than a point estimate.

Urban environments offer wildlife a consistent supply of anthropogenic food waste, divergent from natural food sources in nutrient composition. This study investigates the dietary impact of urbanization on eastern chipmunks (Tamias striatus (Linnaeus, 1758)) by analyzing stable isotope signatures (∂13C and ∂15N) in their hair. The hypothesis posits that chipmunks in urban locales consume more corn-based and high-protein foods, reflected in elevated isotopic signatures compared to their rural counterparts. Sampling encompassed 20 sites across Sudbury, Ontario, varying in urbanization levels. Urbanization was gauged via surveys capturing human activity and sources of anthropogenic food waste. Contrary to expectations, chipmunks did not exhibit δ13C signatures indicative of substantial corn consumption from human food waste. However, δ15N signatures positively correlated with urbanization, suggesting heightened animal protein intake in urban habitats. Elevated δ15N signatures may also result from the use of fertilizers in urban areas . Future avenues involve using stable isotope mixing models to pinpoint dietary sources and exploring the health and reproductive ramifications of urban diets, including effects on gut microbiome composition.

Lake trout (Salvelinus namaycush Walbaum, 1792) forages across macrohabitats (offshore vs nearshore) that likely pose different challenges to the visual system. We examined how differential foraging between macrohabitats challenges the visual system by sampling lake trout from four lakes with differing food web structures (e.g., presence/absence of cisco/smallmouth bass) and evaluating the association between nearshore energy use and visual traits. We found that lake trout foraging more nearshore had relatively larger eyes (corrected for body size) and larger optic tectum size only in lakes with the large pelagic cisco prey absent, while there was no association with these visual traits when cisco was present. Eye shape was not influenced by nearshore foraging. Our results suggest that nearshore foraging challenges the visual system more than offshore foraging but that this may be dependent on important food web structural attributes.

Highly pathogenic avian influenza (HPAI) H5N1 caused mass mortality of wildlife across the North Atlantic in 2022. Following European outbreaks, the first North American case was detected on the island of Newfoundland, Canada in November 2021, before spreading throughout North America. During the following summer, Newfoundland and surrounding islands (NFLD) experienced one of the most significant mortalities in Canadian provinces, with seabirds being the most affected taxa. From surveys and citizen reports, we estimate that 13 517 mortalities that can be attributed to HPAI occurred in NFLD from April to September 2022. Most estimated mortalities were among Northern Gannets (Morus bassanus (Linnaeus, 1758)) (6596), Common Murres (Uria aalge (Pontoppidan, 1763)) (5992), Atlantic Puffins (Fratercula arctica (Linnaeus, 1758)) (282), and Black-legged Kittiwakes (Rissa tridactyla (Linnaeus, 1758)) (217). Mortality reports moved from west to east along the southern, then eastern NFLD coast, and peaked in July and August. We formulated exploratory hypotheses regarding traits that could contribute to infection and mortality. Species differences in mortality most strongly associated with inter-nest distance, breeding phenology, and at-sea overlap with allospecifics from other colonies. Unprecedented seabird mortality and ongoing transmission within the circulating avian influenza viruses highlight the need for continued monitoring and development of conservation strategies.

The heart is an essential organ for survival and reproduction across all animals. In particular, salmonine fishes display vast variability in heart morphology across and even within populations, which often reflects their functional requirements for cardiac output and aerobic capacity. However, changes in heart morphology are not always adaptive, and other factors such as diet can influence heart morphology. A growing concern is the consumption of the thiamine (vitamin B1)-degrading enzyme thiaminase found in some prey species such as rainbow smelt (Osmerus mordax (Mitchell, 1814)). Here, we investigate the association between rainbow smelt consumption and heart morphology in wild lake trout (Salvelinus namaycush (Walbaum in Artedi, 1792)) found in the Sudbury Basin (Ontario, Canada). We found that rainbow smelt consumption is associated with increases in ventricular mass, reductions in ventricular fluid content, and alterations in the allometry of myocardia. We discuss the potential impacts of these changes in heart morphology for the conservation of the species.

The most generalized reproductive mode in anurans is the deposition of egg clutches in water that develop into exotrophic aquatic tadpoles. Yet, despite this extended distribution, cases of parental care on submerged egg clutches are poorly documented. Because of its high diversity, its aquatic habits, and reports on males of two species standing next to the clutch, the Andean genus Telmatobius Wiegmann, 1834 offers an excellent model to examine the evolution of such behavior and the factors influencing it. Here, we combine field and laboratory studies to describe the breeding biology and parental care behavior in Telmatobius culeus (Garman, 1876), Telmatobius hintoni Parker, 1940, Telmatobius intermedius Vellard, 1951, Telmatobius jelskii (Peters, 1873), and Telmatobius oxycephalus Vellard, 1946. Our findings indicate that these five species have prolonged breeding season, and use concealed underwater shelters between rocks or macrophytes for mating and egg deposition. We showed that clutches of 35–560 eggs are deposited in these shelters. Males were observed next to the egg clutch and defending it aggressively against intruders, including conspecifics. Females were, on average, larger than males supporting the hypothesis that competition among males does not drive sexual size dimorphism in the genus. Our findings provide meaningful data to use in conservation programs, given that most species of Telmatobius are considered endangered and fill a significant information gap in understanding parental care’s origin in Nobleobatrachia.

Optimal migration theory predicts birds will follow migration strategies that minimize time, energy, or predation risk, and these strategies employ specific and conflicting behaviours. Many behaviours driving songbird strategies are relatively well known, however gaps remain, especially for spring migration. Here, we describe the behaviours of a short-distance migrant, the Ipswich Sparrow (Passerculus sandwichensis princeps Maynard, 1872), during spring migration. We determined the start and end dates of migration, migratory duration, travel speed, distance per night, and stopover location and duration. We also examined whether behaviours differed by sex and age. Sparrows migrated between March and June, and took an average of 29.1 days at a speed of 7.2 ± 9.4 m/s (SD) to fly ∼1574 km to their breeding grounds. Sparrows flew approximately 100 km/night and made stopovers of >7 days adjacent to ecological barriers. Males migrated before females, and behaviour did not differ with age. Overall, Ipswich Sparrows had a relatively slow travel speed and covered short distances each night consistent with efforts to minimize energy costs or predation risk. They had prolonged stopovers suggesting that they were also trying to minimize time. More work is required to determine which strategy sparrows may be using during spring migration.

An important, but generally overlooked source in intraspecific variability of characters used in tardigrades taxonomy is sexual dimorphism. Dioecious tardigrades species with unisexual or bisexual populations are common, but external sexual dimorphism is rarely observed. The discovery and integrative analysis of a Diploechiniscus species population with high sexual dimorphism from Calvert Island (Canada) has allowed its description as a new species. Diploechiniscus dimorphus n. sp. is characterized by a different chaetotaxy in males and females, and by enlarged cephalic sensory appendages in the males. The discovery of this new species shows that it is important to consider sexual dimorphism as a source of intraspecific variability in tardigrade taxonomy due to its implications on the use of traits commonly used to delineate species such as chaetotaxy. Lastly, the finding of individuals of Diploechiniscus horningi (Schuster and Grigarick, 1971), a species previously synonymized with Diploechiniscus oihonnae (Richters, 1903), allows us to prove that it is genetically a separate species and to reinstate it.

Given the rise in cannabis (Cannabis sativa L.) cultivation, and the absence of disposal guidelines in Canada and other countries, the toxicological impacts of its secondary metabolites on non-target organisms via ingestion are important to understand. Due to the unique chemicals found in C. sativa, sublethal effects, such as those on behaviours and growth, must also be considered. We fed a generalist detritivore, the red wiggler earthworm (Eisenia fetida (Savigny, 1826)), diets composed of hemp or two other crop plants (lettuce or basil), or combinations thereof, over 28 days to measure effects on earthworm survival, growth, and behavioural responses to stressful stimuli (high heat and light). Earthworms fed only hemp gained weight, albeit less than those on other diets, with no effects on their survival or response to light. However, hemp consumption led to slower escape times and speeds from a heat stimulus, indicating potential sublethal effects. By using hemp genotypes with low cannabinoid concentrations, our results offer a conservative estimate of the potential impact of hemp cultivation or disposal of C. sativa on invertebrates such as earthworms. This research underscores the importance of developing accurate risk models for exposure to crop phytochemicals in non-target species.

Long-term and large-scale monitoring of wildlife populations is fundamental to answer questions relevant to conservation. Participatory (or “citizen”) science has become a popular tool to collect additional data and for monitoring trends across larger scales. As white-nose syndrome (WNS), a disease caused by a fungal pathogen, spreads throughout North American bat populations, a participatory science project was initiated in 2012, asking the public to help monitor bat maternity colonies in Quebec, Canada. Using historical data from 1997 to 2011 and the Neighbourhood Bat Watch database from 2012 to 2022, we examined variation in the distribution and size of maternity colonies in relation to WNS invasion and maternity colony exclusions from buildings in Québec. Based on 580 emergence counts from 144 colonies, colony size of little brown bats (Myotis lucifugus (LeConte, 1831)) declined from 77% to 85% during the WNS invasion period, while trends during the epidemic and established periods varied depending on the species and geographical region. Out of the 287 colonies with long-term monitoring, 102 (36%) have subsequently been excluded from buildings. The probability of exclusion was higher in the north than the south, and in houses than in outbuildings. The Neighbourhood Bat Watch allowed us to estimate trends in bat populations and rate of colony exclusions, therefore informing where conservation efforts are most needed.

The introduction of non-indigenous species (NIS) to exotic habitats can have tremendous impacts on native biodiversity, food webs, and ecosystem services. One globally distributed aquatic NIS is the hydrozoan Craspedacusta sowerbii Lankester, 1880. The species’ northern distribution boundary in North America is situated in British Columbia (BC), Canada. It is thus of paramount interest to understand its ecology in this warming invaded habitat, allowing for insights into other regions. Specimens of the genus Craspedacusta have been reported in 34 freshwater systems since August 1990. These reported locations are generally shallow (<10 m), most often of natural origin, and have a small surface area (<0.1 km²). We observed an exponential trend of medusa observations from 1990 till the end of the 2020s. The first seasonal records are in July and the latest in October, with peak sightings reported in August and September. After 2012, regional temperature anomalies during July and August were mostly positive, which overlaps with the period of the majority of reported C. sowerbii sightings. Until this day, all examined medusae are males.

In the migration of young animals, environmental cues can play an outsized role in dispersal, ontogeny, and potentially survival. Identifying and quantifying such cues promotes an understanding of individual species’ migratory evolution and response to long-term environmental change. This study examines weather as a proximate factor for initiating first migration in a wide-ranging subpolar marine predator, the northern fur seal (laaqudax̂, in Unangam Tunuu; Callorhinus ursinus (Linnaeus 1758)). Observations of satellite-telemetered pups on three islands in the eastern Bering Sea, Alaska (US) are used to quantify how inclement weather (high winds, snow, and low temperatures) increases departure rate. Historical weather is then used to reconstruct departure, from the mid-20th century onward. Contemporary surveys provide a test for reconstructed estimates and highlight behavioral processes near the entry to migration. Reconstructions provide novel climate context for large-scale population declines in the eastern Bering Sea since the 1950s; within their limitations, there is a lack of evidence for trends in departure or significant influence on demography. Results here build upon and support historical knowledge regarding the role of weather, while also highlighting potential areas of future study – such as maternal behavior – in influencing the entry into first migration in this species.

Megalobatrachonema nipponicum Yamaguti, 1941 (Nematoda: Cosmocercoidea: Kathlaniidae), the type species of the genus Megalobatrachonema, had been only once reported from the Japanese giant salamander, Andrias japonicus (Temminck, 1836) (Amphibia: Cryptobranchidae), in the last 80 years. Herein, we reported the present species from A. japonicus and hybrids (A. japonicus × Andrias davidianus (Blanchard, 1871)) following the original description. The examined specimens were morphologically identical to the original description. We showed the phylogenetic position of M. nipponicum among cosmocercoid species as well as among congeneric species, which suggested the polyphyly of the genus. In addition, the phylogenetic analysis did not support the subgenera in this genus. Thus, we considered the presence or absence of an esophageal bulb valve as a key morph to identify species, not subgenus, of Megalobatrachonema.

Organisms in seasonal environments respond to both resources in the summer and environmental conditions in winter. Small mammals, in particular, respond quickly to changes in their environment, with many species reliant on the thermal refuge of the subnivium in the winter. However, there has been little research exploring how resources and cold exposure drive the seasonal dynamics of small mammal populations. We studied the populations of three subnivium-specialist small mammal species in seasonally snow-covered forests in Wisconsin, USA across 5 years during summer and winter. In summer, mast availability and canopy cover governed white-footed mouse (Peromyscus leucopus Rafinesque, 1818) populations, coarse woody debris drove short-tailed shrew (Blarina brevicauda Say, 1823) populations, and rainfall influenced red-backed vole (Myodes gapperi (Vigors, 1830)) abundance. Dietary analysis via stable isotopes revealed that shrews primarily consumed arthropods, and mice predominately consumed hard mast despite interannual changes in availability. In winter, white-footed mice and red-backed vole abundances were negatively related to cold exposure. Short-tailed shrew winter population was positively related to their abundances the previous summer. These small mammals responded to species-specific drivers during the growing and snow seasons. Consequently, shorter snow seasons from climate change appear to be restructuring communities by creating a less hospitable environment for winter-adapted species, likely contributing to their regional declines.

During 17 spring and summer field seasons between 1973 and 1999, we documented 220 bouts of nursing by dependent polar bear (Ursus maritimus Phipps, 1774) cubs at Radstock Bay, Nunavut, Canada. The overall mean duration of nursing bouts for cubs-of-the-year (COY) and yearlings (YRLG) litters was 7.1 min (standard deviation (SD) = 3.3, range = 1–23). Mean nursing bout durations of one- and two-cub litters of COY and YRLG in spring and summer seasons ranged from 6.09 to 7.78 min and from 5.00 to 9.18 min, respectively. The overall mean duration of inter-nursing intervals for COY and YRLG litters was 5.7 h (SD = 4.9, range = 0.0–35.0). The mean inter-nursing interval for one-cub litters was 6.4 h (SD = 4.6, range = 0.0–20.2) and for two-cub litters was 5.1 h (SD = 5.1, range = 0.0–35.0). We found no evidence for effects of season or cub age class on nursing behavior. We found weak evidence that two-cub litters nurse slightly longer than one-cub litters, potentially reflecting reduced nursing efficiency due to sibling rivalry. There was neither evidence for diel patterns in nursing behavior nor a detectable relationship between the cessation of nursing and the onset of hunting or sleeping by the adult female.

Emergence of periodical cicadas, Magicicada spp. Davis, 1925, presents an ideal opportunity to study dietary flexibility and selective feeding behavior of bats. It is known that a wide array of taxa prey upon Magicicada spp., but few bat species have been documented to consume them. When larger than typical prey items, such as periodical cicadas, become abundant for a short time frame, insectivorous bats may exhibit alteration in dietary selection that provides insight into capacity and conditions for feeding. Evidence of Magicicada spp. consumption was detected in guano via polymerase chain reaction (PCR) and physical detection in both Eptesicus fuscus (Palisot de Beauvois, 1796) and Myotis lucifugus (Le Conte, 1831), two bat species of different sizes and with different dietary profiles. The consumption of these larger prey items, when they are locally abundant, supports a display of opportunistic behavior and diet flexibility in these two bat species.

Multiple brooding is an important component of reproductive success in many birds and the frequency of this behaviour has been linked to intrinsic (e.g., age, experience) and extrinsic factors (e.g., weather and food availability). When extrinsic factors drive multiple brooding, it may be possible to identify conservation actions to support multiple-brooded species at risk. The Barn Swallow (Hirundo rustica Linnaeus, 1758), is a multiple-brooded aerial insectivore, currently listed as Threatened on Canada’s Species at Risk Act. We examined how weather, landcover, the presence of livestock and metal roofs (with associated heat) above nests affected the likelihood of multiple brooding in Barn Swallows nesting in Nova Scotia and New Brunswick, Canada. We found that sites with a lower proportion of open habitats, including pastures, hayfields, and lawns, within the typical foraging range (i.e., 400 m) of nests, were associated with a higher probability of multiple brooding. Also, multiple brooding may be less likely in windy conditions. We found no effect of proportion of other landcover types, weather conditions, livestock or metal roofs above nests. When possible, decreasing the proportion of open habitats around breeding sites could result in higher rates of multiple brooding, and in turn, help slow population declines.