Characterizing population and individual migration patterns among native and restored bighorn sheep (Ovis canadensis)

Energetic trade-offs in migration decision-making, reproductive effort and subsequent parental care in a long-distance migratory bird

Migratory species trade-off long-distance movement with survival and reproduction, but the spatio-temporal scales at which these decisions occur are relatively unknown. Technological and statistical advances allow fine-scale study of animal decision-making, improving our understanding of possible causes and therefore conservation management. We quantified effects of reproductive preparation during spring migration on subsequent breeding outcomes, breeding outcomes on autumn migration characteristics and autumn migration characteristics on subsequent parental survival in Greenland white-fronted geese (Anser albifrons flavirostris). These are long-distance migratory birds with an approximately 50% population decline from 1999 to 2022. We deployed GPS-acceleration devices on adult females to quantify up to 5 years of individual decision-making throughout the annual cycle. Weather and habitat-use affected time spent feeding and overall dynamic body acceleration (i.e. energy expenditure) during spring and autumn. Geese that expended less energy and fed longer during spring were more likely to successfully reproduce. Geese with offspring expended more energy and fed for less time during autumn, potentially representing adverse fitness consequences of breeding. These behavioural comparisons among Greenland white-fronted geese improve our understanding of fitness trade-offs underlying abundance. We provide a reproducible framework for full annual cycle modelling using location and behaviour data, applicable to similarly studied migratory animals.

Diverse migration patterns and seasonal habitat use of Stone's sheep (Ovis dalli stonei)

We describe temporal and spatial patterns of seasonal space-use and migration by 16 GPS-collared Stone's sheep (Ovis dalli stonei) from nine bands in the Cassiar Mountains of northern British Columbia, Canada. Our objectives were to identify the timing of spring and fall migrations, characterize summer and winter ranges, map and describe migration routes and use of stopover sites, and document altitudinal change across seasons. Our last objective was to assess individual migration strategies based on patterns of geographic migration, altitudinal migration, or residency. Median start and end dates of the spring migration were 12 and 17 Jun (range: 20 May to 05 Aug), and of the fall migration were 30 Aug and 22 Sep (range: 21 Aug to 07 Jan). The median area of winter and summer ranges for geographic migrants were 630.8 ha and 2,829.0 ha, respectively, with a broad range from about 233.6 to 10,196.2 ha. Individuals showed high fidelity to winter ranges over the limited duration of the study. The winter and summer ranges of most individuals (n = 15) were at moderate to high elevations with a median summer elevation of 1,709 m (1,563-1,827 m) and 1,673 m (1,478-1,751 m) that varied <150 m between ranges. Almost all collared females (n = 14) exhibited changes in elevation use that coincide with abbreviated altitudinal migration. Specifically, these females descended to lower spring elevations from their winter range (Δ > 150 m), and then gradually moved up to higher-elevation summer ranges (Δ > 150 m). In the fall, they descended to lower elevations (Δ > 100 m) before returning to their higher winter ranges. The median distance travelled along geographic migration routes was 16.3 km (range: 7.6-47.4 km). During the spring migration, most geographic migrants (n = 8) used at least one stopover site (median = 1.5, range: 0-4), while almost all migrants (n = 11) used stopover sites more frequently in the fall (median = 2.5, range: 0-6). Of the 13 migratory individuals that had at least one other collared individual in their band, most migrated at about the same time, occupied the same summer and winter ranges, used similar migration routes and stopover sites, and exhibited the same migration strategy. We found collared females exhibited four different migration strategies which mostly varied across bands. Migration strategies included long-distance geographic migrants (n = 5), short-distance geographic migrants (n = 5), vacillating migrants (n = 2), and abbreviated altitudinal migrants (n = 4). Different migratory strategies occurred within one band where one collared individual migrated and two did not. We conclude that female Stone's sheep in the Cassiar Mountains displayed a diverse assemblage of seasonal habitat use and migratory behaviors. By delineating seasonal ranges, migration routes and stopover sites, we identify potential areas of priority that can help inform land-use planning and preserve the native migrations of Stone's sheep in the region.

Population genetic variation characterization of the boreal tree Acer ginnala in Northern China

Genetic diversity and differentiation are revealed particularly through spatio-temporal environmental heterogeneity. Acer ginnala, as a deciduous shrub/small tree, is a foundation species in many terrestrial ecosystems of Northern China. Owing to its increased use as an economic resource, this species has been in the vulnerability. Therefore, the elucidations of the genetic differentiation and influence of environmental factors on A. ginnala are very critical for its management and future utilization strategies. In this study, high genetic diversity and differentiation occurred in A. ginnala, which might be resulted from its pollination mechanism and species characteristics. Compared with the species level, relatively low genetic diversity was detected at the population level that might be the cause for its vulnerability. There was no significant relationship between genetic and geographical distances, while a significant correlation existed between genetic and environmental distances. Among nineteen climate variables, Annual Mean Temperature (bio1), Mean Diurnal Range (bio2), Isothermality (bio3), Temperature Seasonality (bio4), Precipitation of Wettest Month (bio13), Precipitation Seasonality (bio15), and Precipitation of Warmest Quarter (bio18) could explain the substantial levels of genetic variation (> 40%) in this species. The A. ginnala populations were isolated into multi-subpopulations by the heterogeneous climate conditions, which subsequently promoted the genetic divergence. Climatic heterogeneity played an important role in the pattern of genetic differentiation and population distribution of A. ginnala across a relatively wide range in Northern China. These would provide some clues for the conservation and management of this vulnerable species.

Drought reshuffles plant phenology and reduces the foraging benefit of green-wave surfing for a migratory ungulate

To increase resource gain, many herbivores pace their migration with the flush of nutritious plant green-up that progresses across the landscape (termed "green-wave surfing"). Despite concerns about the effects of climate change on migratory species and the critical role of plant phenology in mediating the ability of ungulates to surf, little is known about how drought shapes the green wave and influences the foraging benefits of migration. With a 19 year dataset on drought and plant phenology across 99 unique migratory routes of mule deer (Odocoileus hemionus) in western Wyoming, United States, we show that drought shortened the duration of spring green-up by approximately twofold (2.5 weeks) and resulted in less sequential green-up along migratory routes. We investigated the possibility that some routes were buffered from the effects of drought (i.e., routes that maintained long green-up duration irrespective of drought intensity). We found no evidence of drought-buffered routes. Instead, routes with the longest green-up in non-drought years also were the most affected by drought. Despite phenological changes along the migratory route, mule deer closely followed drought-altered green waves during migration. Migrating deer did not experience a trophic mismatch with the green wave during drought. Instead, the shorter window of green-up caused by drought reduced the opportunity to accumulate forage resources during rapid spring migrations. Our work highlights the synchronization of phenological events as an important mechanism by which climate change can negatively affect migratory species by reducing the temporal availability of key food resources. For migratory herbivores, climate change poses a new and growing threat by altering resource phenology and diminishing the foraging benefit of migration.

Individual variation creates diverse migratory portfolios in native populations of a mountain ungulate

Ecological theory and empirical studies have demonstrated population-level demographic benefits resulting from a diversity of migratory behaviors with important implications for ecology, conservation, and evolution of migratory organisms. Nevertheless, evaluation of migratory portfolios (i.e., the variation in migratory behaviors across space and time among individuals within populations) has received relatively little attention in migratory ungulates, where research has focused largely on the dichotomous behaviors (e.g., resident and migrant) of partially migratory populations. Using GPS data from 361 female bighorn sheep (Ovis canadensis) across 17 (4 restored, 6 augmented, 7 native) populations in Montana and Wyoming, USA, we (1) characterized migratory portfolios based on behavioral and spatial migratory characteristics and (2) evaluated the relative influence of landscape attributes and management histories on migratory diversity. Native populations, which had been extant on the landscape for many generations, had more diverse migratory portfolios, higher behavioral switching rates, reduced seasonal range fidelity, and broad dispersion of individuals across summer and winter ranges. In contrast, restored populations with an abbreviated history on the landscape were largely non-migratory with a narrow portfolio of migratory behaviors, less behavioral switching, higher fidelity to seasonal ranges, and less dispersion on summer and winter ranges. Augmented populations were more variable and contained characteristics of both native and restored populations. Differences in migratory diversity among populations were associated with management histories (e.g., restored, augmented, or native). Landscape characteristics such as the duration and regularity of green-up, human landscape alterations, topography, and snow gradients were not strongly associated with migratory diversity. We suggest a two-pronged approach to restoring migratory portfolios in ungulates that first develops behavior-specific habitat models and then places individuals with known migratory behaviors into unoccupied areas in an effort to bolster migratory portfolios in restored populations, potentially with synergistic benefits associated with variation among individuals and resulting portfolio effects. Management efforts to restore diverse migratory portfolios may increase the abundance, resilience, and long-term viability of ungulate populations.

Releases of Asian houbara must respect genetic and geographic origin to preserve inherited migration behaviour: evidence from a translocation experiment

Maintaining appropriate migratory strategies is important in conservation; however, translocations of migratory animals may alter locally evolved migration behaviours of recipient populations if these are different and heritable. We used satellite telemetry and experimental translocation to quantify differences and assess heritability in migration behaviours between three migratory Asian houbara (Chlamydotis macqueenii) breeding populations (640 km range across eastern, central and western Uzbekistan). Adults from the eastern population migrated twice as far (mean = 1184 km ± 44 s.e.) as the western population (656 km ± 183 s.e.) and showed significantly less variation in migration distance than the central population (1030 km ± 127 s.e.). The western and central populations wintered significantly further north (mean: +8.32° N ± 1.70 s.e. and +4.19° N ± 1.16 s.e., respectively) and the central population further west (-3.47° E ± 1.46 s.e.) than individuals from the eastern population. These differences could arise from a differing innate drive, or through learnt facultative responses to topography, filtered by survival. Translocated birds from the eastern population (wild-laid and captive-reared, n = 5) migrated further than adults from either western or central recipient populations, particularly in their second migration year. Translocated birds continued migrating south past suitable wintering grounds used by the recipient populations despite having to negotiate mountain obstacles. Together, this suggests a considerable conserved heritable migratory component with local adaptation at a fine geographic scale. Surviving translocated individuals returned to their release site, suggesting that continued translocations would lead to introgression of the heritable component and risk altering recipient migration patterns. Conservation biologists considering translocation interventions for migratory populations should evaluate potential genetic components of migratory behaviour.