Foraging benefits promote fitness in migratory mule deer

Anna C. Ortega; Tayler N. LaSharr; Patrick W. Burke; Patrick Lionberger; Miguel Valdez; Kevin L. Monteith; Matthew J. Kauffman

doi:10.1016/j.cub.2025.12.030

USGS · 70274035

Foraging benefits promote fitness in migratory mule deer

Anna C. Ortega·Tayler N. LaSharr·Patrick W. Burke·Patrick Lionberger·Miguel Valdez·Kevin L. Monteith·Matthew J. Kauffman

View original source ↗Export metadata ↓

Abstract

Although migration is widespread among ungulates, the fitness benefits associated with different migratory tactics have rarely been documented. Here, we evaluated a 9-year dataset on a migratory population of mule deer to test the hypothesis that long-distance migration provides access to seasonal forage which translates into demographic benefits. Mule deer that migrated long (>130 km) and medium distances (50–130 km) accessed higher forage quality and thus gained 1.3–2.7 times more fat over the growing season compared to mule deer that remained year-round as residents within a desert ecosystem. Elevated levels of fat translated to ∼20% higher probability of adult annual survival than residents. Mule deer that remained year-round in the desert portion of the study area were so resource-limited that they raised fawns at the expense of their own survival. Due to their higher levels of fat, annual survival, and fetal rates, migrants showed more robust population growth (λ = 1.03) compared to residents, which exhibited projected declines in population size over time (λ = 0.95). These results support the notion that migration translates into demographic benefits and highlight the urgent conservation work necessary to sustain diverse ungulate migrations amid habitat alteration due to climate change and an expanding web of linear barriers to movement.

Explore related subjects

Current Biology Article

Source-reported bounding extent: 42.046057654877615° to 43.1858103856338° latitude; -110.3710872029688° to -108.94810270575864° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Anna C. Ortega, Tayler N. LaSharr, Patrick W. Burke, Patrick Lionberger, Miguel Valdez, Kevin L. Monteith, Matthew J. Kauffman. 2026. Foraging benefits promote fitness in migratory mule deer. https://doi.org/10.1016/j.cub.2025.12.030

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related USGS reports

USGS2026

Space-based monitoring of penguin diet links sea ice, food webs, and population change

Rapid environmental change is reshaping Antarctic ecosystems through shifts in temperature and sea ice dynamics, with implications for species such as the iconic Adélie penguin ( Pygoscelis adeliae ). Because Antarctic predators rely on a relatively small number of key prey resources in the region 1 whose life histories are intrinsically linked to sea ice, 2 , 3 these abiotic changes are expected to cascade through food webs. However, the scale and remoteness of Antarctica have limited efforts to link environmental change to ecological responses across the continent. Combining tools from imaging spectroscopy, stable isotope analysis, and hierarchical statistical modeling, we reconstructed Adélie penguin diet across the entirety of the species’ global range over a three-decade period (1984–2013) using satellite imagery from the Landsat program. This approach leveraged the distinct spectral properties (a generalized measure of color) of penguin guano as observed by satellites, 4 , 5 which vary according to penguin diet. 6 , 7 We found pronounced differences in diet across the continent and that year-to-year dietary shifts were strongly associated with sea ice dynamics. Higher sea ice corresponded to more fish-based diets, whereas lower sea ice was associated with a greater reliance on krill. Additionally, spatial differences in penguin diet were associated with long-term trends in penguin abundance, linking food web processes to large-scale population dynamics. This study represents the first use of satellite observations to capture trophic dynamics at continental and decadal scales and highlights how environmental change might restructure Antarctic food webs and influence the future of a key sentinel species.

Current Biology↗

USGS2025

Population genomics of recovery and extinction in Hawaiian honeycreepers

Native Hawaiian forest birds are experiencing an unprecedented extinction crisis. In particular, the iconic Hawaiian honeycreeper radiation has declined to just 17 out of ∼60 species remaining, most threatened with extinction due to avian malaria. Here, we investigate the genomic signatures of these declines in three honeycreeper species: the critically endangered ʻakikiki ( Oreomystis bairdi ) and ʻakekeʻe ( Loxops caeruleirostris ) and the extinct poʻouli ( Melamprosops phaeosoma ). Surprisingly, we find that Hawaiian honeycreepers, even the last known po‘ouli individual, maintain high heterozygosity compared with other island birds, reflecting historically large population sizes. This high heterozygosity may contribute to an elevated impact of inbreeding depression, as evidenced by reduced survival and reproductive success among highly inbred ‘akikiki. Demographic analysis revealed that recent precipitous declines in ‘akikiki and ‘akekeʻe coincide with the spread of avian malaria in the late 20 th century, consistent with malaria being the primary driver of population collapse. Using predictive population viability modeling, we explore potential recovery scenarios for ʻakekeʻe, which has recently declined below 100 individuals in the wild. Our models predict that, under current conditions, ‘akekeʻe is likely to go extinct in the near future. However, if mosquito control campaigns are effective at reducing malaria, recovery can still occur. These findings emphasize the urgency of ongoing mosquito control efforts, demonstrating hope for a species nearing the brink of extinction. More broadly, our study provides a detailed examination of genomic diversity, inbreeding depression, and extinction risk in a collapsing adaptive radiation, with implications for conservation of other endangered island species.

Hawaii↗

USGS2023

Genetic architecture and evolution of color variation in American black bears

Color variation is a frequent evolutionary substrate for camouflage in small mammals, but the underlying genetics and evolutionary forces that drive color variation in natural populations of large mammals are mostly unexplained. The American black bear, Ursus americanus ( U. americanus ), exhibits a range of colors including the cinnamon morph, which has a similar color to the brown bear, U. arctos , and is found at high frequency in the American southwest. Reflectance and chemical melanin measurements showed little distinction between U. arctos and cinnamon U. americanus individuals. We used a genome-wide association for hair color as a quantitative trait in 151 U. americanus individuals and identified a single major locus (p < 10 −13 ). Additional genomic and functional studies identified a missense alteration (R153C) in Tyrosinase-related protein 1 ( TYRP1 ) that likely affects binding of the zinc cofactor, impairs protein localization, and results in decreased pigment production. Population genetic analyses and demographic modeling indicated that the R153C variant arose 9.36 kya in a southwestern population where it likely provided a selective advantage, spreading both northwards and eastwards by gene flow. A different TYRP1 allele, R114C, contributes to the characteristic brown color of U. arctos but is not fixed across the range.

Current Biology↗