We have just completed our 42nd photographic capture-recapture survey to identify individual giraffes in the Tarangire-Manyara Ecosystem in Tanzania. We began with a pilot study in 2011, and since 2012 have regularly conducted 6 annual surveys of these iconic mega-herbivores to understand where they are doing well, where they are not, and why. Our goal is to identify what is good for giraffes and what harms giraffes, so we can conserve these animals for future generations.
As always, we thank our funders without whom we could not do this important work.
Seeing Spots: New Study Reveals the Giraffe Babies Inherit Spot Patterns from Their Mothers and Certain Spot Traits Improve Newborn Survival
50-year-old Hypothesis Confirmed with Modern Techniques
Giraffe spots are distinctive and beautiful, as shown by the popularity of giraffe patterns in fashion and design. But how giraffe patterns came to be and what purpose they serve in the wild was a mystery until this week. Dr. Derek Lee, associate research professor at Penn State University and principal scientist at the Wild Nature Institute published the results of a study today that revealed wild giraffe spot patterns are heritable, with elements of the pattern passed down from mother to offspring, and certain spot traits improved survival for newborns. Coats with complex patterns are found on many mammal species from anteaters to zebras, and these pelage traits are hypothesized to improve survival and reproduction by affecting predator and parasite evasion, temperature regulation, and social communication. This study was the first to examine complex mammal coat markings as individual traits that might have fitness consequences. Dr. Lee said, “Quantifying heritability and fitness consequences of mammal coat pattern traits will help us understand how and why complex coat patterns evolved in wild animals.”
Dr. Anne Innis Dagg, the first giraffe field researcher in Africa, presented evidence in 1968 that the shape, number, area, and color of spots in giraffe coat patterns may be heritable, but her analysis came from a small zoo population. Forty-nine years later, Lee’s study used a new dataset and modern analysis to confirm Dagg’s hypothesis. The heritability finding was neither surprising nor original, but science advances through replication of studies and the slow accumulation of evidence. The novel aspects of Lee’s study were the use of image analysis software to objectively measure various traits present in giraffe coat patterns, and statistics to quantify the heritability and fitness consequences of the patterns.
The spot pattern traits of circularity and jaggedness of edge were passed from mother to offspring, and variation in the coat patterns of 258 giraffe calves significantly affected their survival during the first few months of life, suggesting spot traits may be associated with anti-predator camouflage. Coauthor Monica Bond, doctoral candidate in ecology at the University of Zurich and principal scientist at the Wild Nature Institute, noted “Survival in the wild is precarious, and any small advantage such as what these spot traits provided, can mean the difference between an individual’s life and death.”
Spot traits might also serve other adaptive functions such as social communication, kin recognition, or thermoregulation, and might be associated with other fitness aspects like survival or fecundity of older giraffes. Giraffe skin color is grey, but the spots that make up their fur coat markings are highly variable in color and shape. Because each animal’s patterns are unique and do not change with age, natural coat patterns identify individuals, so wildlife conservation researchers like Dr. Lee use the patterns to study animals without the need for dangerous and traumatic captures.
“Now that we know that genetic variation underlies spot pattern variation in giraffes it should be possible with the aid of the giraffe genome sequence to discover the specific genes that determine spot patterns.“ noted Douglas Cavener, Professor of Biology and Verne M. Willaman Dean of the Penn State Eberly College of Science, and coauthor of the paper. Lee said, “My hope is that other scientists will use the same tools to measure the traits of complex mammal coat patterns and this will advance our understanding of what these patterns mean.”
Giraffes are vulnerable to extinction with a 40% decline over the past few decades. The Wild Nature Institute is running the world’s largest giraffe research project in northern Tanzania, and their results are informing species conservation and the field of evolutionary ecology.
Lee DE, Cavener DR, Bond ML. 2018. Seeing spots: Quantifying mother-offspring similarity and assessing fitness consequences of coat pattern traits in a wild population of giraffes (Giraffa camelopardalis). PeerJ. doi: 10.7717/peerj.5690.
Dr. Derek Lee, Monica Bond, and James Madeli with some little fans of Juma the Giraffe, at our office in Mtowambu, Tanzania.
Wild Nature Institute is happy to announce that all three of our “Africa’s Giants” children’s books are available for purchase online at Amazon and Barnes and Noble. Juma the Giraffe, Our Elephant Neighbours, and Helping Brother Rhinoceros teach ecological and social lessons for children ages 3-7. Your purchase supports efforts to study and protect these magnificent giants in the wild, and buys a version of the book in Swahili for an African child. To learn more about each book, visit africasgiants.org.
TO ORDER, CLICK ON LINKS BELOW
· A new study found community-based wildlife conservation in Tanzania can quickly result in clear ecological success by benefitting giraffes and other wildlife species.
Arusha, TANZANIA, 10 August 2018-
Community-based natural resource management is a grassroots conservation tool that has become one of the dominant paradigms of natural resource conservation worldwide. In Tanzania, efforts to decentralize wildlife management to local communities occur through the creation of Wildlife Management Areas, where several villages set aside land for wildlife conservation in return for the majority of tourism revenues from the area. Nineteen Wildlife Management Areas are currently operating, encompassing 7% (6.2 million ha) of Tanzania’s land area, with 19 more planned.
In a paper published this week in the Journal of Wildlife Management, Dr. Derek E. Lee from Penn State University and the Wild Nature Institute documented significantly higher densities of wildlife in a community Wildlife Management Area relative to an unprotected control site. Dr. Lee said, “Measuring wildlife responses in Wildlife Management Areas is important for evaluating the effectiveness of specific projects and the general concept of community-based natural resource management. My data demonstrated that establishment of the Burunge Wildlife Management Area and increased support of the village rangers there had positive ecological outcomes in the form of higher wildlife densities and higher giraffe population growth. Hopefully these results will encourage more community-based conservation efforts.” The new paper adds to one previous examination of the wildlife conservation efficacy of Wildlife Management Areas.
Tanzania’s wildlife resources are among the finest in the world, including the last intact fully functioning savanna wilderness ecosystems in Africa with the largest terrestrial mammal migration and a high density of big game. According to the World Travel and Tourism Council, tourism in Tanzania generates around USD $6 billion annually. Tourism brings in 25% of the county’s foreign exchange earnings and regularly surpasses the minerals and energy sectors. Tourism represents 13% of Tanzania’s total GDP, and employs around 700,000 people directly and 1.5 million people indirectly. Dr. Philp Muruthi, Senior Director of Conservation Science for the African Wildlife Foundation said, “It is very gratifying to see the positive role of community conservation areas in saving Africa’s endangered and declining species. Clearly to save the giraffe will take more than the formal national parks. And the benefits to the species and landowners are immense into the future.”
However, profitable wildlife resources are threatened by human and economic forces. There is higher human population density and higher incidence of poverty around protected areas relative to other rural communities, and the rural poor around protected areas depend on bushmeat for the majority of protein in their diets. Additionally, there are complex and non-intuitive interactions among wildlife ecology, the tourism economy, agricultural production, and infrastructure development that complicate the perceived tradeoff between wildlife conservation and human economic development. A World Bank bioeconomic analysis found that ostensibly positive economic developments such as higher-intensity tourism, mining, road development, and agriculture which degrade existing wildlife resources would result in an overall loss to the Tanzanian economy. Although most community-based natural resource management programs have only limited success at achieving both conservation and human development goals, the concept appears to be the best opportunity for Tanzania to retain its place as one of the most famous and profitable wildlife tourism destinations while also sustainably developing other economic sectors and alleviating rural poverty.
Wildlife Management Areas can also play an important role in maintaining migratory habitat for wildebeest, zebra, oryx, eland, and gazelle. The Tarangire Ecosystem, which includes Burunge Wildlife Management Area, hosts one of the last three long-distance wildebeest migrations remaining in the world, and Wildlife Management Areas conserve landscape connectivity and freedom to roam for highly mobile wildlife and Maasai livestock keepers. Lee said, “Long distance migrations of wildlife perform rare and essential ecosystem services that shape and maintain African savanna rangelands, and community-based Wildlife Management Areas are important components of a functioning migratory landscape.”
Lee DE. 2018. Evaluating Conservation Effectiveness in a Tanzanian Community Wildlife Management Area. Journal of Wildlife Management. DOI: 10.1002/jwmg.21549.
On August 2, the Living Desert Zoo and Gardens hosted Wild Nature Institute's Derek Lee, David Brown, and Monica Bond for two fun-filled, productive days in Palm Desert, California. The Living Desert promotes desert conservation through preservation, education and appreciation by preserving a large portion of its grounds in a natural state, fostering appreciation of deserts worldwide through interpretive exhibits, helping build up populations of endangered desert species, and financially supporting education and conservation that protects desert species. We are deeply grateful to the Living Desert for being our partners in our "Celebrating Africa's Giants" education program for the conservation of giraffes, elephants, and rhinoceroses.
The Living Desert staff were wonderful hosts, showing us around their beautiful grounds and introducing us to all the animals - including their herd of giraffes! Monica enjoyed feeding Twiga a few carrots. We also visited the zoo's Tanzanian Schoolhouse, where children read our storybook Juma the Giraffe and do the hands-on activities that accompany the book - so learning about giraffes can be fun!
We presented our conservation science and education work to 85 zoo staff and members.
We are working closely with the Living Desert conservation and education staff, who are applying their considerable skills and talents towards helping us to develop our Celebrating Africa's Giants educational materials and to promote these materials for use in zoos that hold giraffes, elephants, and rhinos throughout the USA. Thank you Living Desert, and we look forward to expanding our programs together.
The goal of Wild Nature is to understand where giraffes and other ungulates are doing well and where they are not, and why, and to protect and connect the places most important for wildlife and nomadic Maasai people. The ecological resiliency of a large landscape like the Tarangire Ecosystem is reinforced when all the parts are conserved.
Wild Nature Institute is conducting the world’s largest individual-based study of Maasai giraffes (Giraffa camelopardalis tippelskirchii). We use pattern-recognition software to track more than 3,000 individuals in a 4,000-square kilometer area to understand births, deaths, and movements in the fragmented Tarangire Ecosystem. Our results inform conservation and land management, and help ensure a future for giraffes and Maasai people. Here is a summary of what we’ve discovered about wildlife in Tarangire that will help conserve these magnificent mega-herbivores throughout Tanzania.
Precision, accuracy, and costs of survey methods for giraffe Giraffa camelopardalis was one of our first publications from the project. We estimated giraffe density and abundance in the Tarangire Ecosystem in northern Tanzania using two ground survey methods—distance sampling and capture-mark-recapture—and compared our ground-based estimates with those from the most recent aerial survey. We found aerial survey estimates were biased low, while ground-based surveys were more precise and cost less. However, aerial surveys are useful over large regions of Tanzania and thus can provide landscape-scale population estimates. We computed correction factors to improve the accuracy of aerial surveys and suggested ways to further improve aerial survey methods.
Our two papers about Giraffe Skin Disease (GSD), The occurrence and prevalence of giraffe skin disease in protected areas of northern Tanzania, and Soil correlates and mortality from giraffe skin disease in Tanzania described the disorder in the Journal of Wildlife Diseases. We documented that GSD prevalence was best explained by soil fertility, with less disease prevalence on more fertile soils. We found no mortality effect of GSD on adult giraffe in Tarangire National Park. Based on our findings, GSD is unlikely to warrant immediate veterinary intervention, but continued monitoring is recommended to ensure early detection if GSD-afflicted animals begin to show signs of increased mortality or other adverse effects.
In Spatial variation in giraffe demography: a test of 2 paradigms, we examined whether spatial variation in demography of a tropical mega-herbivore (the giraffe) followed the “temporal paradigm” or the “adult survival paradigm” of ungulate population dynamics that were formed from temperate-zone studies. We quantified how giraffe demographic rates of survival and reproduction varied across space at regional (northern Tanzania) and continental (Africa-wide) scales. Spatial variability of demographic rates at the continental scale supported the temporal paradigm of low variability in adult survival and more highly variable reproduction and calf survival. In contrast, at the regional scale, adult female survival had higher spatial variation, which supported the adult survival paradigm. At both scales, variation in adult female survival made the greatest contribution to variation in local population growth rates. We also found human-caused reductions in adult female giraffe survival are the most likely reasons of population declines.
In Giraffe demography and population ecology, we summarized current knowledge of demography and population ecology of giraffes and provided a framework for using population models when developing and evaluating conservation and management efforts for giraffes (or other large herbivore species).
In Migratory herds of wildebeests and zebras indirectly affect calf survival of giraffes, we utilized our data about a large-mammal predator–prey savanna food web to evaluate support for 2 hypotheses relating to the indirect effects of “apparent competition” and “apparent mutualism.” We examined how the presence of migratory herds of wildebeests (Connochaetes taurinus) and zebras (Equus quagga) affected survival of resident giraffe calves, as mediated by their shared predator, African lions (Panthera leo). African lions are generalist predators whose primary, preferred prey are wildebeests and zebras, but lion predation on secondary prey such as giraffes may change according to the relative abundance of the primary prey species. We found that local lion predation pressure on giraffes was reduced by local density of wildebeests and zebras, making giraffe neonatal and calf survival probabilities higher when the migratory herds were present. This supported the apparent mutualism hypothesis.
Natural predation had a significant effect on giraffe calf and neonate survival, and could significantly affect giraffe population dynamics, thus if wildebeest and zebra populations in this ecosystem continue to decline as a result of increasingly disrupted migrations and poaching, then giraffe calves will face increased predation pressure as the predator–prey ratio increases. Our results suggest that the widespread population declines observed in many migratory systems are likely to trigger demographic impacts in other species due to indirect effects like those shown here.
We were proud to contribute to the IUCN Red List Assessment for giraffes, which reclassified giraffes as Vulnerable due to an observed population decline of 36–40% over three generations (30 years, 1985–2015). The factors causing this decline (direct killing and habitat loss) have not ceased throughout the species’ range. The best available estimates indicate a total population in 1985 of 151,702–163,452 giraffes (106,191–114,416 mature individuals), and in 2015 a total population of 97,562 giraffes (68,293 mature individuals). Some giraffe populations are stable or increasing, while others are declining, and each population is subject to pressure by threats specific to their local country or region. The populations of giraffes are scattered and fragmented with different growth trajectories and threats, but the species trend reveals an overall large decline in numbers across its range in Africa.
We also documented for the first time that Season of birth affects juvenile survival of giraffe. Variation in timing of reproduction and subsequent juvenile survival often plays an important role in population dynamics of ungulates in temperate and boreal regions. Tropical ungulates often give birth year round, but survival effects of birth season for tropical ungulate species were previously unknown. We found significant differences in juvenile survival according to season of birth, with calves born during the dry season experiencing the highest survival probability. Phenological match (matching birth season with vegetation growth) may explain the juvenile survival advantage to offspring born during the dry season from 1) greater accumulated maternal energy reserves in mothers who conceived in the long rainy season, 2) high-protein browse in the late dry-early short rainy seasons supplementing maternal and calf resources, 3) reduced predation due to decreased stalking cover, or some combination of these. Asynchrony is believed to be the ancestral state of all ungulates, and this investigation illustrated how seasonal variation in vegetation can affect juvenile survival and may have played a role in the evolution of synchronous births.
We also contributed to a lively discussion about How many species of giraffe are there? Giraffes are presently classified as one species, with nine subspecies. A paper in Current Biology presented DNA data and a taxonomy with four species of giraffe. The present consensus of one species divided into nine subspecies had previously been questioned several times over the past few decades. We presented the various taxonomic schemes and offered that the fundamental reason for different taxonomic interpretations is that they are based upon different datasets that adopt different statistical techniques and follow different criteria. These different taxonomies create a basis for future taxonomy discussions and conservation efforts.
Movements and source–sink dynamics of a Masai giraffe metapopulation provided a regional metapopulation analysis of the Tarangire ecosystem to inform conservation management for Masai giraffes in five subpopulations defined by land management designations. We assessed the source–sink structure of the study population, and we created a matrix metapopulation model to examine how variation in demographic components of survival, reproduction, and movement affected metapopulation growth rate. Movement data indicated no subpopulation was completely isolated, but movement probabilities varied among subpopulations. Source–sink statistics and flow of individuals indicated three subpopulations were sources, while two subpopulations were sinks. We found areas with higher wildlife protection efforts and fewer human impacts were sources, and less-protected areas were identified as sinks. Our results highlight the importance of identifying source–sink dynamics among subpopulations for effective conservation planning and emphasize how protected areas can play an important role in sustaining metapopulations.
The Tarangire migration is one of only three long distance migrations of wildebeest (Connochaetes taurinus) remaining in Africa. The wildebeest population in the Tarangire Ecosystem of northern Tanzania decreased from an estimated 40,000 animals in 1988 to approximately 7000 today. We used A multi-method approach to delineate and validate migration corridors for wildebeest to inform rangeland conservation and land use planning. Conserving landscape-scale migratory habitat for wildebeest will also protect important rangelands for Maasai pastoralists and their livestock.
Two papers explored the Ecological effectiveness of community-based Wildlife Management Areas (WMAs). In Tanzania, community-based natural resource management (CBNRM) of wildlife occurs through WMAs. The WMAs consist of multiple villages designating land and managing it for wildlife conservation in return for a portion of subsequent tourism revenues. In Randilen WMA, we documented significantly higher densities of resident wildlife (giraffes and dik-diks) and lower densities of cattle in the WMA, relative to the control site, indicating short-term ecological success. In a paper about to be published using data from Burunge WMA, we found greater densities of wildlife and lower densities of livestock inside the WMA compared with outside. After management changes, we documented significantly higher densities of several wild ungulate species and lower densities of domestic ungulates in the WMA. These combined results indicate the ecological effectiveness of Randilen and Burunge WMAs and provide evidence that CBNRM can have positive effects on wildlife populations, particularly when support to grassroots law enforcement is provided.
We are currently collecting more data and conducting lots more analyses that will investigate juvenile dispersal, giraffe social structure, how sociality affects survival and reproduction, and other interesting topics. Learn more about our work at www.WildNatureInstitute.org .
D.E. Lee & M.L. Bond. 2016. "Precision, accuracy, and costs of survey methods for giraffe Giraffa camelopardalis." Journal of Mammalogy 79:940-948.
D.E. Lee, B.M. Kissui, Y.A. Kiwango & M.L. Bond. 2016. "Migratory herds of wildebeest and zebra indirectly affect juvenile survival of giraffes." Ecology and Evolution DOI: 10.1002/ece3.2561.
D.E. Lee & M.K.L. Strauss. 2016. "Giraffe demography and population ecology." Reference Module in Earth Sciences and Environmental Studies. DOI: 10.1016/B978-0-12-409548-9.09721-9.
D.E. Lee, M.L. Bond, B.M. Kissui, Y.A. Kiwango & D.T. Bolger. 2016. "Spatial variation in giraffe demography: a test of 2 paradigms." Journal of Mammalogy 79:1015-1025.
D.E. Lee & M.L. Bond. 2016. "The occurrence and prevalence of giraffe skin disease in protected areas of northern Tanzania." Journal of Wildlife Diseases 52:753-755.
M.L. Bond, M.K.L. Strauss & D.E. Lee. 2016. "Soil correlates and mortality of giraffe skin disease in northern Tanzania." Journal of Wildlife Diseases DOI:10.7589/2016-02-047.
Z. Muller, F. Bercovitch, J. Fennessy, D. Brown, R. Brand, M. Brown, D. Bolger, K. Carter, F. Deacon, J. Doherty, S. Fennessy, A.A. Hussein, D. Lee, A. Marais, M. Strauss, A. Tutchings & T. Wube. 2016. "Giraffa camelopardalis." The IUCN Red List of Threatened Species 2016: e.T9194A51140239.
F.B. Bercovitch, P.S. Berry, A. Dagg, F. Deacon, J.B. Doherty, D.E. Lee, F. Mineur, Z. Muller, R. Ogden, R. Seymour & B. Shorrocks. 2017. "How many species of giraffe are there?" Current Biology 27:R136-R137.
D.E. Lee & D.T. Bolger. 2017. "Movements and source-sink dynamics among subpopulations of giraffe." Population Ecology DOI 10.1007/s10144-017-0580-7.
D.E. Lee, M.L. Bond & D.T. Bolger. 2017. "Season of birth affects juvenile survival of giraffe." Population Ecology 59:45-54 DOI 10.1007/s10144-017-0571-8.
M.L. Bond, C.M. Bradley, C. Kiffner, T.A. Morrison, D.E. Lee. 2017. “A multi-method approach to delineate and validate migratory corridors.” Landscape Ecology 32:1705-1721.
D.E. Lee, M.L. Bond. 2018. “Quantifying the ecological success of a community-based wildlife conservation area in Tanzania.” Journal of Mammalogy 99:459-464.
D.E. Lee. 2018. “Evaluating Conservation Effectiveness in a Tanzanian Community Wildlife Management Area.” Journal of Wildlife Management in press.
July 27, 2018
by George Wuerthner
Published today in CounterPunch.
“What but the wolf’s tooth whittled so fine the fleet limbs of the antelope?” wrote the poet Robinson Jeffers.
Jeffers encapsulated the idea that evolutionary processes shape all plants and animals. Unfortunately, far too many in the Forest Service and the collaboratives that work with them fail to understand this basic idea—a “healthy” forest is one with many sources of mortality. Chainsaws are no substitute for natural processes.
Recently on a collaborative/forest service field tour, participants were shown some fir trees with root rot. The group was told that the forest was “too dense” and thus the trees had become susceptible to root rot. The solution, of course, was to log (read kill) the fir trees so they would not succumb to root rot and die.
When I asked the collaborative members and agency personal assembled, “What was the ecological role of root rot in the ecosystem?”, I got perplexed blank stares.
It appeared that no one had ever considered such a question. Yet here they were anxious to log the forest based on the assumption that root rot killing trees was something to control or remove from the forest ecosystem.
Among the ecological values that root rot may provide to the forest ecosystem is a natural thinning of trees (unlike logging/thinning that lost money, root rot does this at no cost to taxpayers). Root rot selects for those trees less adapted to current and future climatic conditions, plus creates snags and dead wood that is critical to many wildlife species. The snags store carbon, and when trees fall over, they establish hummocky mounds that result in micro-sites for plants and animals.
The issue of root rot is a good example of where the Forest Service and collaborative members fail to see the forest (ecosystem) through the trees.
Throughout the field trip, I was told the goal of logging was to “restore” forests so the trees would be “resilient” and less vulnerable to evolutionary processes like wildfire, drought, mistletoe, bark beetles, and root rot. But there is much more to a forest ecosystem than trees.
Whether implicitly acknowledged, the focus on trees represents an Industrial Forestry paradigm that views trees as fodder for wood products. For many species of plants and animals, dead trees are critical to their survival.
For instance, some 45% of all birds rely on snags for feeding, nesting, and rooting. Bats find shelter under the bark of dead trees. Small mammals from voles to marten hide beneath or inside downed logs. And some 50% of the aquatic habitat in small to medium sized streams is the result of fallen logs in the water.
Most foresters will acknowledge grudgingly that some limited mortality from wildfire, drought, root rot, bark beetles and other natural agents may be acceptable, but they seldom promote the idea that these drivers of evolution are critical to the “health” of our forest ecosystems.
Just as wolves help to maintain healthy elk and deer herds, other evolutionarily processes like wildfire, bark beetles, mistletoe, and root rot maintain healthy forest ecosystems.
However, the Forest Service is focused on managing trees, not ecosystems. What they are doing is “restoring” the “structure”, not the evolutionary processes that have for millennia shaped and honed our forest ecosystems.
The way you build “resilience” into the forest is by protecting, preserving and enhancing the ecological and evolutionary processes that have created the forest. Nature is much better at selecting which trees should survive than a forester with a paint marking can.
If we wish to build resilience into our forests, we must maintain the ecological and evolutionary processes that “whittles” the ecosystem.
George Wuerthner has published 36 books including Wildfire: A Century of Failed Forest Policy. He serves on the board of the Western Watersheds Project.
New Research by Wild Nature Institute Shows Wildfire Has More Benefits than Costs to Spotted Owl Populations
Wildfire Management Designed to Protect Spotted Owls May Be Outdated
24 July 2018
Forest fires are not a serious threat to populations of Spotted Owls, contrary to current perceptions and forest management strategies. According to a new study, mixed-severity fires actually are good for Spotted Owl populations, producing more benefits than costs to the species, which acts as an indicator of biological health to the old-growth forests where they live. The study, which analyzed all 21 published scientific studies about the effects of wildfires on Spotted Owls, appears July 24 in the journal Ecosphere and suggests that management strategies for this species are outdated.
“Current management strategies targeted at protecting Spotted Owls are prioritizing what is called fuel-reduction logging, which removes trees and other vegetation in a misguided and ineffectual attempt to reduce the severity of future fires,” said Derek E. Lee, associate research professor of biology at Penn State and author of the paper. “But this tactic removes canopy cover and large trees that are important for Spotted Owls and does not generally reduce fire severity of big, hot fires. The idea behind these logging projects is that the risks from wildfire outweigh the harm caused by additional logging, but here we show that forest fires are not a serious threat to owl populations and in most instances are even beneficial. This reveals an urgent need to re-evaluate our forest management strategies.”
Spotted Owls are found in old-growth forests in the western United States and act as an indicator species, a measure of the biological health of an area, for public-land management. This species is particularly sensitive to logging, and when the northern subspecies of Spotted Owl was listed in 1990 as threatened -- likely to become endangered in the foreseeable future -- under the federal Endangered Species Act, about 90% of America’s old-growth forest had already been lost to unsustainable logging practices over the previous 50 years. The listing of the Northern and Mexican Spotted Owls as threatened drew national attention to the dramatic decline of old-growth forest ecosystems and forced policy changes in the management of national forests.
In spite of these protections, populations of Spotted Owls have continued to decline outside of national forests over the last 38 years. Although many believe that wildfire has significantly contributed to this decline, there is little scientific basis for this assumption.
“Much of what we knew about the Spotted Owl’s habitat preferences was derived from studies in areas that had not recently experienced fire,” said Lee. “I analyzed all available published studies investigating the effects of forest fires on Spotted Owls. I also considered the influence of fire severity. Forest fires in the western United States typically burn as mixed-severity fires that include substantial patches of low-, moderate-, and high-severity fire.”
The new study shows that mixed-severity fires do not have any significantly negative effects on the owls’ choice of foraging habitat, survival, occupancy, reproduction, or recruitment.
Although mixed-severity fires may lead to reduced occupancy -- the probability that certain sites are occupied by owls -- in burned areas, this reduction is less than is typically seen due to normal movement of the owls in unburned habitat, and is much less than what is observed in response to logging. Additionally, the risk of fire occurring in spotted owl breeding sites is very small: only 1 percent of breeding sites are affected by mixed-severity fires each year.
Mixed-severity fires have a positive impact on the owls’ choice of foraging habitat, on the number of owls that are recruited to the area immediately after a fire, and on reproduction. High-severity fires, including those that burn 100 percent of an area, are also positively associated with reproduction. This indicates that even the most intense fires can have positive outcomes for Spotted Owls.
“These positive effects indicate that the mixed-severity fires of recent decades, including so-called megafires that have been receiving lots of media attention lately, are within the natural range of variability for these forests,” said Lee. “The fact that Spotted Owls are adapted to these types of fires tells us that they have seen this before and learned to take advantage of it.”
Together, these results suggest that, contrary to current perceptions, forest fires do not appear to be a serious threat to owl populations, and may impart more benefits than costs for Spotted Owls. Therefore, fuel-reduction logging treatments intended to mitigate fire severity in Spotted Owl habitat may in fact do more harm than good.
“Spotted Owls were once a symbol of the biodiversity found in old-growth forests,” said Lee. “We need to reevaluate our management strategies to better protect these birds and the extraordinary biodiversity found in severely burned forests.”
Derek E. Lee: DerekLee@psu.edu, (415) 763-0348
Gail McCormick: email@example.com, (814) 863-0901
Science News and Updates From the Field from Wild Nature Institute.
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