Animal migration amid shifting patterns of phenology and predation: lessons from a Yellowstone elk herd

In the paper

“high annual NDVI increments (i.e., rapid vegetation emergence) have been negatively related to juvenile growth and survival (Pettorelli et al. 2007).”

What the sources say

• Supported

  The Discussion reports a negative effect of rapid green-up on juvenile growth and an associated negative effect on survival. The Vegetation dynamics and early performance section specifies that the relationship varied by population: maximal NDVI increase was not related to mountain goat kid survival at Caw Ridge. (LLM, conf=0.91)

  cites Pettorelli et al. 2007 source

In the paper

“Indeed, elk density and winter severity have been decreasing in the system for many years (Wilmers andGetz 2005, Eberhardt et al. 2007).”

What the sources say

• Partly supported

  The Weather Data Analysis and Discussion sections report declining winter snow depth and a shorter period of snow cover since 1948, supporting the winter-severity part of the claim. They do not report that elk density has been decreasing for many years; the Discussion instead predicts higher elk densities if snow levels continue to decline. Page numbers are not available in our copy. (LLM, conf=0.87)

  cites Wilmers and Getz 2005 sourceExperimental — accuracy not yet measured
• ?Not checked — no full text of the sourcecites Eberhardt et al. 2007 source

In the paper

“In recent years, however, concern has grown over global declines in ungulate migration, including such diverse species as wildebeest (Connochaetus taurinus), saiga (Saiga tatarica), pronghorn (Antilocapra americana), and caribou (Rangifer tarandus) (Berger 2004, Bolger et al. 2008, Festa-Bianchet et al. 2011).”

What the sources say

• ?Not checked — no full text of the sourcecites Berger 2004 source
• ?Not checked — no full text of the sourcecites Bolger et al. 2008 source
• Supported

  The Caribou declines section reports that some western mountain caribou herds have stopped migrating between traditional seasonal ranges. That supports the caribou example for which this source is cited; the sentence also cites other works for the other species. (LLM, conf=0.88)

  cites Festa-Bianchet et al. 2011 source

In the paper

“Prior research has revealed diverse influences of recent drought on the region's wildfire activity and snowpack (Westerling et al. 2006), amphibian populations (McMenamin et al. 2008), and bat reproduction (Adams 2010).”

What the sources say

• ?Not checked — no full text of the sourcecites Westerling et al. 2006 source
• Supported

  The Abstract links recent drought and wetland desiccation to severe declines in Yellowstone amphibians. The Results likewise report reduced amphibian populations and diversity linked to changes in the region’s hydrology. The other effects in the citing sentence are attributed to different sources. (LLM, conf=0.94)

  cites McMenamin et al. 2008 source
• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites Adams 2010

In the paper

“In migratory birds in Europe, such a mismatch between the springtime arrival of migrants and the phenology of their breeding range may be linked to recent population declines (Both et al. 2006).”

What the sources say

• Partly supported

  The supplementary Table 1A reports recent population declines in several pied flycatcher populations in the Netherlands and gives caterpillar peak dates for their breeding areas. The passages available from our copy do not establish a mismatch between spring arrival and breeding-range phenology or link that mismatch to the declines. (LLM, conf=0.78)

  cites Both et al. 2006 sourceExperimental — accuracy not yet measured

In the paper

“This latter finding is consistent with the observations that elk in Yellowstone do not strongly avoid wolves during winter (Fortin et al. 2005, Mao et al. 2005) and do not avoid foraging on two preferred browse species, willow and aspen, even in high-risk areas of the ecosystem (Creel et al. 2009, Kauffman et al. 2010).”

What the sources say

• ?Not checked — no full text of the sourcecites Fortin et al. 2005 source
• ?Not checked — no full text of the sourcecites Mao et al. 2005 source
• Partly supported

  The Abstract reports that elk shifted from grazing to browsing when wolves were present, which supports the general point that they continued to browse. It does not identify willow or aspen, or establish that elk continued foraging on those species in high-risk areas. The winter wolf-avoidance clause is attributed to other citations in the citing sentence. (LLM, conf=0.82)

  cites Creel et al. 2009 sourceExperimental — accuracy not yet measured

In the paper

“In the only prior case for ungulates that we know of, recent arctic warming advanced vegetation green-up more rapidly than female caribou (Rangifer tarandus) advanced their parturition date, with negative effects on calf production (Post and Forchhammer 2008).”

What the sources say

• Supported

  The Results and discussion report that plant growth advanced by approximately two weeks while the onset of caribou parturition remained comparatively stable. They link that shift to increased calf mortality and a fourfold decline in calf production. The phrase “only prior case known to the authors” describes the citing authors’ knowledge, not a finding attributed to this source. (LLM, conf=0.93)

  cites Post and Forchhammer 2008 source

In the paper

“recent work found no differences in the body fat levels and pregnancy rates of Yellowstone elk before and after wolf reintroduction (White et al. 2011).”

What the sources say

• Partly supported

  The Abstract reports nearly identical age-adjusted body fat before and after wolf restoration, and the Results report similar pregnancy rates for elk aged 4–9 years. But the Results also report higher post-wolf body fat and pregnancy rates for elk older than 9 years. Thus, saying there were no differences across Yellowstone elk overgeneralizes the findings. (LLM, conf=0.89)

  cites White et al. 2011 sourceExperimental — accuracy not yet measured

In the paper

“some caribou declines may be linked to subtler changes in plant phenology, fire regimes, the accessibility of caribou to their predators, and densities of alternative prey (Vors andBoyce 2009, Festa-Bianchet et al. 2011).”

What the sources say

• Supported

  The Conclusion (page not provided) links changes in plant phenology to reduced calf production and higher calf mortality, and reports that increased forest-fire frequency has adversely affected caribou condition and movement. The section on spatiotemporal species overlap explains how alternative prey support more predators and increase predation pressure on caribou. Together, these passages support the claim’s cautious wording that such changes may be linked to some declines. (LLM, conf=0.87)

  cites Vors and Boyce 2009 source
• Partly supported

  The Boreal and Mountain caribou section links declines to habitat changes, predation, altered alternative-prey abundance, and wolves’ travel efficiency; it also says increasing fire events could reduce recruitment and survival. The Migratory Tundra caribou section discusses changing plant-growth timing, but says that change may benefit caribou rather than linking it to declines. No page numbers were available in our copy. (LLM, conf=0.82)

  cites Festa-Bianchet et al. 2011 sourceExperimental — accuracy not yet measured

In the paper

“population declines may be linked to trophic mismatch (Both et al. 2006)”

What the sources say

• ?Could not verify

  The supplementary table lists pied flycatcher population trends and caterpillar peak dates, but does not say that a mismatch between breeding and food availability is linked to the declines. Searches for “mismatch” and for breeding timing relative to caterpillar peaks found no decisive passage; the main article text appears absent from our copy. (LLM, conf=0.70)

  cites Both et al. 2006 sourceExperimental — accuracy not yet measured

In the paper

“we detected no influence of density dependence (regression of calf : cow ratio on abundance, F 1,12 ¼ 1.0, P ¼ 0.34) or winter severity (regression of calf : cow ratio on cumulative snow water equivalent [Wolverine Creek SNO-TEL, 10 km northwest of the core winter range of migrants], F 1,21 ¼ 3.02, P ¼ 0.1).”

In the paper

“coincident with warmer spring-summer temperatures and reduced spring precipitation”

In the paper

“In contrast, among resident elk, we have recently observed increasing recruitment and a high rate of pregnancy.”

In the paper

“Long-term monitoring has revealed an associated shift in the spatial distribution of the population over 21 years, driven by high recruitment levels (see Fig. 2A) and eastward expansion in the resident subpopulation (Appendix A).”

In the paper

“We detected a similar warming trend on the year-round range of resident elk, but no change in spring precipitation (Appendix D).”

In the paper

“Though only 0.01% of the residents' year-round range is irrigated, 23% (3/13) of resident females spent 47-52% of their time in irrigated fields during July and August.”

In the paper

“Calf recruitment of resident elk declined to a breakpoint (2002 6 1.5, P , 0.001), then steadily increased (F 1,19 ¼ 5.71, P ¼ 0.007; Fig. 2A).”

In the paper

“The calf : cow ratio of resident elk (gray circles) declined to a breakpoint (2002 6 1.5, P , 0.001) and then steadily increased (F 1,21 ¼ 5.71, P ¼ 0.007).”

In the paper

“From 1989 to 2009, maximum NDVI increment (C) did not change on the resident range but (D) increased on the migratory range”

In the paper

“Over the same period, green-up duration (E) did not change on resident range but (F) decreased on migratory range”

In the paper

“Lactating females were pregnant at a lower rate than non-lactators in the migratory population, whereas lactation did not affect the pregnancy rate of residents.”

In the paper

“Several wolf packs now occupy the year-round range of migratory elk (pack numbers shown above bars), but only one pack has occupied the resident elk range.”

In the paper

“The body fat (mean þ SE) of lactating migrants was significantly lower than that of non-lactating migrants, but did not differ from that of lactating residents.”

In the paper

“A one-sided K-S test (see Results) indicated that migratory elk had a higher proportion of older individuals than the residents, consistent with recent reductions in calf recruitment.”

In the paper

“The number of grizzly bear (Ursus arctos) groups (shown with fitted solid line and 95% CI in dashed lines) counted during summer observation flights from 1990 to 2008 within the year-round range of migratory elk increased over 21 years (no grizzlies were observed in flights over the range of resident elk).”

In the paper

“Peak protein intake of temperate mountain ungulates has been shown to coincide with the annual maximum increment in NDVI (Hamel et al. 2009)”

What the sources say

• ?Not checked — no full text of the sourcecites Hamel et al. 2009 source

In the paper

“Agency observations were classified at the subpopulation level based on winter range associations of migratory and resident elk established previously via very high frequency (VHF) telemetry (Rudd et al. 1983), and validated through our own Global Positioning System (GPS) collaring during 2007-2010.”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites Rudd et al. 1983

In the paper

“Migration is thought to have evolved in ungulates because in seasonal environments it affords prolonged access to high-quality forage and can reduce predator exposure (Fryxell and Sinclair 1988).”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites Fryxell and Sinclair 1988

In the paper

“Accordingly, the migrations of species such as Serengeti wildebeest, and Greater Yellowstone elk (Cervus elaphus) and mule deer (Odocoileus hemonius) track vegetation green-up (Holdo et al. 2009, White et al. 2010, Sawyer and Kauffman 2011).”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites Holdo et al. 2009
• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites White et al. 2010
• ?Not checked — no full text of the sourcecites Sawyer and Kauffman 2011 source

In the paper

“In contrast, resident elk are likely subsidized by the removal of large carnivores and by irrigated agriculture, contributing to their recent expansion.”

In the paper

“Thus, reduced mortality due to predation is thought to benefit migratory individuals by increasing juvenile survival (Bolger et al. 2008).”

What the sources say

• ?Not checked — no full text of the sourcecites Bolger et al. 2008 source

In the paper

“In relatively pristine landscapes, such fitness benefits have promoted the abundance of migratory ungulates, which can outnumber their resident counterparts in some cases by an order of magnitude (Fryxell et al. 1988).”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites Fryxell et al. 1988

In the paper

“For instance, in the Serengeti Ecosystem, predation was found to be lower for migratory than for resident wildebeest (Sinclair 1984), and in Alberta, migratory elk reduced their wolf exposure by 70% in comparison with resident elk (Hebblewhite and Merrill 2007).”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites Sinclair 1984
• ?Not checked — no full text of the sourcecites Hebblewhite and Merrill 2007 source

In the paper

“The influence of differential carnivore recovery and predation on the performance of partially migratory elk has previously been investigated in and around Banff National Park (BNP) in Alberta, Canada.”

In the paper

“suggesting a summer influence on the probability of conception that is at odds with the proposed mechanism.”

In the paper

“For instance, sexual maturity was delayed in populations of European red deer (Cervus elaphus) that experienced warmer springs and advanced phenology (Langvatn et al. 1996), probably because of reduced growth rates among calves and yearlings (Cook et al. 2004a).”

What the sources say

• ?Not checked — no full text of the sourcecites Langvatn et al. 1996 source
• ?Not checked — no full text of the sourcecites Cook et al. 2004a source

In the paper

“Fluctuations in short-term energy balance are known to influence the pregnancy probability of domestic ungulates (e.g., National Research Council 1985, Fitz-Rodriguez et al. 2009), and may occur without large changes in body fat levels.”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites National Research Council 1985
• ?Not checked — no full text of the sourcecites Fitz-Rodriguez et al. 2009 source

In the paper

“recent studies have described regional climatic changes as anomalous (within 1000-year [Pederson et al. 2011] and 14 000-year [Shuman 2011] contexts) and consistent with anthropogenic forcing (Barnett et al. 2008, Shuman 2011).”

What the sources say

• ?Not checked — no full text of the sourcecites Pederson et al. 2011 source
• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites Shuman 2011
• ?Not checked — no full text of the sourcecites Barnett et al. 2008 source

In the paper

“The latter climate effect was thought to be mediated by a nutritional limitation on lactating females, similar to recent findings among Rocky Mountain bats, including migratory populations (Adams 2010).”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites Adams 2010

In the paper

“Additionally, newly reintroduced wolves caused 15-17% of calf deaths, favoring young calves in summer (Barber-Meyer et al. 2008).”

What the sources say

• ?Not checked — no full text of the sourcecites Barber-Meyer et al. 2008 source

In the paper

“Recent increases in the recruitment of resident elk are consistent with a likely nutritional subsidy from irrigated fields, coupled with lower rates of calf predation by grizzlies and wolves.”

In the paper

“An additional factor contributing to the reduced pregnancy rate of the migratory subpopulation was its older age structure (Fig. 3B), a likely result of sustained low recruitment in recent years.”

In the paper

“A secondary reason put forth for the historical dominance of migratory ungulates is that their seasonal movements reduce their exposure to predation (Fryxell et al. 1988, Fryxell andSinclair 1988).”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites Fryxell et al. 1988
• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites Fryxell and Sinclair 1988

In the paper

“During that study, bears (primarily grizzlies) caused 58-60% of calf deaths (Barber-Meyer et al. 2008), more than three times the proportion estimated 15 years earlier in the same area 1).(Singer et al. 1997).”

What the sources say

• ?Not checked — no full text of the sourcecites Barber-Meyer et al. 2008 source
• ?Not checked — no full text of the sourcecites Singer et al. 1997 source

In the paper

“Our findings newly link the region's drought to changes in vegetation phenology and the demographic benefits of ungulate migration.”

In the paper

“By contrast, in the year-round habitats of resident elk, large carnivores are limited by management removals following livestock depredations, and bears may be further limited by a low tolerance for human activity.”

In the paper

“This apparent decline in the demographic benefits of migration coincided with growing numbers of large carnivores that prey on elk calves and a severe, long-term drought that appears to have reduced habitat quality.”

In the paper

“The low pregnancy rate of migrants resulted in part from poor reproduction of young and lactating females (Fig. 3B, C), consistent with prior study of ungulates under nutritional limitation.”

In the paper

“Overall, warmer temperatures and reduced precipitation appear to facilitate rapid growth of vegetation and reduce the time in which it is available to Yellowstone migrants on their summer range.”

In the paper

“Female elk under nutritional stress may give birth to lighter calves with reduced growth rates, which can increase the window of calf vulnerability and risk of calf mortality (Singer et al. 1997, White et al. 2010).”

What the sources say

• ?Not checked — no full text of the sourcecites Singer et al. 1997 source
• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites White et al. 2010

In the paper

“Though birds are also known to benefit from abundant resources (Levey and Stiles 1992) and reduced predation risk (McKinnon et al. 2010) on disparate seasonal ranges”

What the sources say

• ?Not checked — no full text of the sourcecites Levey and Stiles 1992 source
• ?Not checked — no full text of the sourcecites McKinnon et al. 2010 source

In the paper

“human influences on seasonal resource availability and nest predation have long been a concern in studies of Neotropical migratory birds (Robinson et al. 1995).”

What the sources say

• ?Not checked — no full text of the sourcecites Robinson et al. 1995 source

In the paper

“As land migrants, ungulates appear particularly vulnerable to the physical obstruction of their migration routes in comparison with other migratory taxa.”