Tag Archive | "endangered species"

Graphium sarpedon

Paying the Price of Extinction Debt

The fact that species are being lost at an unprecedented rate is not in dispute, but how can conservation biologists who are trying to create protected areas account for extinctions which are occurring today because of events in the past?

Extinction is a natural process, but the current rate of species loss – at least 100 times what would be expected under normal conditions1 – is anything but natural. It is common knowledge that species are being lost as a result of human activities, but the fact that extinctions can occur because of historical events as well as contemporary pressures is less well known. This phenomenon is called extinction debt2 and has been documented by researchers working in a range of habitats3, 4, 5.

When an area of habitat becomes fragmented, the isolated patches which remain are not able to support the same array of species as the intact site due to a reduction in the amount of available resources. Over time, many of the species trapped within the patch will die off until, eventually, a new equilibrium is reached and the patch is only occupied by the species that it is able to support. The time taken for equilibrium to be reached is known as “relaxation time”3, because the habitat patch is relaxing back to equilibrium after a considerable disturbance.

In 2012, researchers from Japan studied the diversity of butterflies in a range of habitat patches scattered across Tokyo. They discovered that existing species richness was more closely correlated with the habitat conditions of 1971 than present day habitat conditions5, an indication of an extinction debt that has yet to be paid. They also mapped the predicted extinction debt of different habitat patches and found that the loss of species from large patches is likely to be lower than the loss from small patches5.

Graphium sarpedon

Graphium sarpedon, the blue triangle butterfly, is frequently found in Tokyo, where Soga and Koike (2012) mapped the potential extinction debt of butterfly species found in habitat patches in urban environments.

Source: Wikimedia Commons

Maps which indicate where biodiversity is likely to decline in the future can be used to inform prioritization. Instead of focusing limited resources on the protection of areas that are projected to lose biodiversity, conservation practitioners can more optimally focus their efforts on areas where species are more likely to persist into the future. Prioritization can even be based around the newly emerging concept of “conservation credit”6, which accounts for the colonization of newly suitable habitat by species from other areas.

However, it is important to remember that the disturbances and fragmentation leading to species loss through extinction debt are, in the majority of cases, the result of human activities. Extinction debt doesn’t just illustrate the complexity of the current biodiversity crisis; it emphasizes the importance of protecting habitat in the present in order to secure biodiversity into the future.


1. Pimm, S.L., and C.N. Jenkins. 2005. Sustaining the Variety of Life. Scientific American 293: 66 – 73
2. Tilman, D., R.M. May, C.L. Lehman, and M.A. Novak. 1994. Habitat destruction and the extinction debt. Nature 317: 65 – 66
3. Diamond, J.M. 1972. Biogeographic kinetics: estimation of relaxation times for avifaunas of southwest Pacific islands. PNAS 69: 3199 – 3203
4. Krauss, J., R. Bommarco, M. Guardiola, R.K. Heikkinen, A. Helm, M. Kuussaari, and R. Lindborg. 2010. Habitat fragmentation causes immediate and time‐delayed biodiversity loss at different trophic levels. Ecology Letters 13: 597 – 605
5. Soga, M. and S. Koike. 2012. Mapping the potential extinction debt of butterflies in a modern city: implications for conservation priorities in urban landscapes. Animal Conservation 16: 1 – 11
6. Vellend. M., and H.M. Kharouba. 2013. Setting conservation priorities when what you see is not what you get. Animal Conservation 16: 14 – 15

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Preserving the Genetic Diversity of Endangered Species

Preserving the Genetic Diversity of Endangered Species

How can conservationists prioritize species that are already classified as endangered? The answer to this difficult question might just be hidden inside the genes of the endangered species themselves.

Conservation resources might be finite, but the threats to our natural world are not. With so many species struggling to survive, it is more important than ever for conservationists to use their limited funding in the most effective (and efficient) way possible. But how are conservationists supposed to decide which endangered species should be given top priority? In the past, the value of a species – whether economic or social – was the dominant factor when it came to directing funding. In recent years, however, the science of prioritization has become an increasingly important aspect of conservation biology1. One emerging form of scientific prioritization focuses on a relatively new way of measuring the value of a species: their genetic uniqueness.

Genetic uniqueness, also known as evolutionary distinctiveness, is a way of prioritizing species that takes into account the relationships between species groups. According to this method, a species with a lot of close relatives should not be prioritized over a species with no close relatives, which will have been designated its own branch in the tree of life. While every species is genetically unique, most species share some of their genes with their close relatives. (Just look at chimpanzee and bonobos, which share 99.6% of their DNA with each other and 98.7% of their DNA with another close relative, humanity2.) This means that species with few or no close relatives contain genes that can’t be found in any other species.

Darwin's Tree of Life

Charles Darwin’s preliminary sketches of the tree of life were some of the earliest attempts to establish the relationship between species. By using our modem understanding of these relationships, scientists can prioritize genetically unique species for conservation.

Source: http://www.nhm.ac.uk/

Why are genes so important when it comes to setting priorities for conservation? Genes are the building blocks of life. They determine the characteristics of a species and, through the process of natural selection, help species to adapt to future conditions3. By preserving genetically unique species instead of lots of genetically similar species, conservationists stand a better chance of maintaining the essential foundations of ecosystems that are ready to survive whatever the future has in store. Given the uncertainties of climate change, this adaptability will be even more important in the decades to come.

Although it would be naïve to assume that conservation can take place without taking into account the social and economic aspects of conservation, studies have shown that species with a high level of genetic uniqueness are actually more threatened than other species4, 5, 6.Whatever method of prioritization is favored, time is of the essence when it comes to conserving the genetic heritage of the species that share our planet.


1. Game, E.T., P. Kareiva, and H.P. Possingham. 2013. Six Common Mistakes in Conservation Priority Setting. Conservation Biology 27: 480 – 485
2. Science Now. 2012. Bonobos Join Chimps as Closest Human Relatives. Available at: http://news.sciencemag.org/sciencenow/2012/06/bonobo-genome-sequenced.html/ [Accessed 2/7/2013]
3. Crozier, R., P-M. Agapow , and M.A. Smith. 2009. Conservation genetics: from species to habitats. Biology International 47: 73 – 79
4. Redding, D.W., and A.Ø. Mooers. 2006. Incorporating Evolutionary Measures into Conservation Prioritization. Conservation Biology 20: 1670 – 1678
5. Daru, B.H., K. Yessoufou, L.T. Mankga, and T.J. Davies. 2013. A Global Trend Towards the Loss of Evolutionarily Unique Species in Mangrove Ecosystems. PLoS ONE 8: e66686
6. Isaac, N.J., S.T. Turvey, B. Collen, C. Waterman, and J.E. Baillie. 2007. Mammals on the EDGE: Conservation Priorities Based on Threat and Phylogeny. PLoS ONE 6: e296

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“Carrying capacity”: What Can Managed Relocation Do For Climate Adaptation?

A recent paper co-authored by Defenders President and CEO Jamie Clark highlights the conflicting and complex aspects of managed relocation, a conservation measure where species, populations, or genotypes are intentionally introduced outside of their historical range for the purpose of maintaining biological diversity or ecosystem functioning.  In the context of the paper, it is considered as an adaptation strategy to climate change, but it could also be a strategy for other types of conservation planning.

This is a valuable paper, especially because it summarizes very well the many potential problems and the conflicting issues with managed relocation, and how they relate to a possible and much needed future policy to guide such process. The authors state that, while managed relocation has been happening intentionally and non-intentionally around the world, many issues exist that would need to be addressed once this strategy starts being considered more often.  Problems and conflicts span the ethical, scientific, and cultural fields, and the authors stress the point that evidence to support managed relocation decisions is essential.  They mention the need of using decision theory to weigh such scientific, ethical, and cultural, as well as cost considerations, and call for collaborative efforts involving specialists that can effectively address the full range of said considerations.  They also bring up the issue of the accuracy of species distribution models under climate change, and their usefulness (or lack thereof) in predicting future ranges and habitats. Climate change is expected to affect the future range of many species due to its effects not only on the species themselves, but also on their habitats and essential interactions.  However, species distribution models do not account for the complexity of species interactions and needs, or for the maintenance of essential ecosystem services and processes in which each species is involved.  Caution is needed when using that type of data to inform managed relocation.

The question remains of what “appropriate managed relocation actions” (and/or “efforts”) are, but the paper cites some general criteria to help determine the appropriateness of a managed relocation action (e.g., when data suggest that the extinction risk of a species without relocation is high, relocation is feasible, and the relocation is unlikely to cause substantial harm to the proposed site).  The paper includes a list of key ethical, ecological, legal and policy, and integrated questions to base a decision framework on managed relocation.  Questions such as “which conservation goals take ethical precedence over others and why?”, “what are the limits of less dramatic alternatives to managed relocation, such as increasing habitat connectivity?”, and “what constitutes an acceptable risk of harm and what are adequate measures for the protection of recipient ecosystems?” can effectively help guide the decision making process.  Together with their recommendations, these questions provide very good guidance for a future policy regulating managed relocation.

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Lake Erie watersnake recovery is a success for the ESA – and for invasive species?

Photo courtesy of Richard King. Lake Erie watersnake (bottom), with two closely related specimens. The Lake Erie watersnake has fully recovered from the threat extinction thanks to the ESA, and will soon be delisted.

This past Tuesday, the U.S. Fish and Wildlife Service announced that the Lake Erie watersnake, Nerodia sipedon insularum is now fully recovered and will be removed from the federal endangered species list (76 Fed. Reg. 50680). With a population of just under 10,000 snakes in 2010 (almost two times the recovery target), the Lake Erie watersnake joins the ranks of the bald eagle, the Aleutian Canada goose, the American alligator, and 18 other species that have come back from the brink of extinction, thanks to the regulatory protections and conservation measures of the Endangered Species Act (ESA). This event comes as a welcome victory after furious debates over a rider-ridden House Interior Appropriations bill in July and early August. The watersnake’s delisting is a success that proves the ESA is not broken, as critics are wont to declare, and instead reinforces the Act’s long record of success.

Listed as ‘threatened’ only 12 years ago, the Lake Erie watersnake’s recovery story has a twist to it: its remarkable resurgence was, in part, made possible by an “invasive” species, the round goby. Since the round goby first appeared in Lake Erie in the early 1990s, the watersnake’s diet has changed from being based on native fishes and amphibians to a diet composed of more than 90% round goby, with remarkable consequences – increased watersnake growth rates, increased body size, and increase in fecundity, with female watersnakes producing on average 25% more offspring post-invasion (Richard B. King Laboratory, Northern Illinois University). Increase in benthic fish biomass in Lake Erie increased prey availability, effectively dismissing the issue of low watersnake fecundity; the round goby’s success in the ecosystem means that the watersnake has a significant and secure prey source for years to come.

The narrative of the Lake Erie watersnake’s recovery adds an interesting dimension to discourse on invasive species and how we evaluate their impacts on ecosystems. While the majority of the literature focuses on the detrimental effects invasives have on the adopted environment (Byers 2002, Fritts and Leasman-Tanner 2001, Rhymer and Simberloff 1996, etc.), the potential benefits to ecosystems deserves the scientific community’s attention, and calls for an honest appraisal of the current stigma against invasive species.

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A fair scale for mitigation

A fair scale for mitigation

Compensatory mitigation projects that fully offset development-incurred losses are, unfortunately, far and few.  When it comes to biodiversity, species decline continue.  ‘Restoration at multiple trophic levels’ (2003), by Deborah French McCay and Jill J. Rowe, laid out a novel approach to compensatory mitigation, based on the North Cape oil spill, presenting a new framework for estimating the appropriate scale of restoration: primary production, across multiple trophic levels.

Aerial view of the January 19, 1996 North Cape oil spill, with the tug boat Scandia in the upper portion of the photo, and the tank barge North Cape in the lower portion. An estimated 828,000 gallons were spilled, resulting in hundreds oiled birds and large numbers of lobsters, surf clams and sea stars found dead on the beach. The North Cape oil spill is considered to be an important legal precedent since it was the first major oil spill to occur after the 1990 Oil Pollution Act, passed in the wake of the devastating Exxon Valdez spill in Alaska. Photography by E.R. Gundlach.

Having concluded that species impacted by the North Cape spill would benefit especially from habitat restoration, McCay and Rowe’s model “builds upon food chain energetic and habitat equivalency analysis, […] convert[ing] losses of production of multiple species to an energetically equivalent single trophic level so that the scale of necessary compensatory restoration can be computed.”  So, food webs and trophic energy efficiencies can be used to pinpoint the level at which restoration appropriately compensates for the total spill-related injury; trophic level dynamics would then ensure that the system would return to a normal balance.  Additionally, McCay and Rowe correct for the delay between injury and restoration by considering the biomass directly lost plus that not produced at a 3% annual discount rate, as recommended by NOAA.  Thus, they came to the conclusion that restoration of around 20 acres of highly productive eelgrass beds, combined with ongoing recovery activities, would sufficiently compensate for spill injuries with no net loss.

McCay and Rowe are the first to admit that their model presents shortcomings linked to the uncertainty that lies in estimate-driven modeling, and the use of primary production as a proxy for multiple ecosystem processes.  Nonetheless, they argue that “[u]sing production as the scaling metric also allows for differences in body size and growth rate between the individuals killed and the ones added by restoration while still achieving equivalence and thus compensatory replacement.”  While conceding their model has room for improvement, they assert that they have opened up new paths for research – a different ecosystem function may be a more suitable vector for evaluating restoration benefits, and needs only to be discovered.

Example of trophic pyramid, from National Park Service. In McCay and Rowe's model, development incurred-loss of consumers (herbivores and carnivores) can be appropriately offset through primary production.

While this approach, as interpreted for an oil spill, lacks the advantage of species specificity, it presents an exciting venue for compensatory mitigation and endangered species incidental take permits (ITPs).  Rooted in sound understanding of species and habitat interactions, mitigation could compensate for take of listed species to a standard that sustains ecosystem processes and adequately offsets the loss caused, without being arbitrary or punitive to the developer.  The current incidental take calculation process is far from perfect, and the adoption of objective and appropriate mitigation scaling could bring ITPs one step closer to their intended purpose: to strike a balance between development interests and species recovery efforts.

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Bog Turtle

Saving America’s smallest turtle

Bog Turtle

Bog Turtle, Scienceray

Programs like the U.S. Department of Agriculture’s Wetlands Reserve Program rely on voluntary conservation measures, providing financial support to private landowner’s wetlands restoration and conservation projects.   The Federal government is able to obtain conservation easements with landowners, and provides cost-share payments for wetland rehabilitation practices and the implementation of conservation measures, like setting up fences around identified habitat.  The hope of making a small profit can do a lot to convince a cost-conscious landowner to take the steps necessary to protect endangered species on their property, demonstrating the great potential of incentives in species recovery on private lands.

Why is this important?

Because the majority of America’s endangered species depend on private land for their survival; indeed, private land comprises 80 percent of threatened and endangered species habitat (Crouse et al. 2002).  What’s more, most of these species need active habitat restoration and management, and not just protection, in order to thrive.  Consider the threatened bog turtle, America’s most diminutive turtle.

Infant bog turtle, from turtlesandmoreturtles.blogspot.com

Bog turtle distribution map

The bog turtle is found from Maryland to New York in small isolated wetlands at the headwaters of the region’s streams and rivers (see distribution map on the left).  We tried to catch up with bog turtles on a recent survey of wetlands in Chester County, Pennsylvania, with expert herpetologists, Jason Tesauro and Brandon Ruhe.

We had high hopes of seeing a lot of bog turtles, but instead found some fresh tracks, and happened upon three box turtles.  According to Jason and Brandon, prime viewing time for bog turtles actually occurs earlier in the spring, and in the fall.  In the summer months, they prefer to retreat into the underbrush and burrow into the mud, living off a healthy diet of slugs and other prey.  It is also possible that we simply did not spot them; wetland meadows, sunny but moist, are optimal habitat, but over the course of the years bog turtle habitats have turned into overly dense thickets often consisting of invasive plants – the dense vegetation made our search more difficult.

Example of agriculture-related development near bog turtle habitat.

Nearby agricultural activity and development has resulted in secondary impacts, most notably nutrient loading.  An enriched soil mineral content is a haven for invasive plants and may have caused the unnaturally productive growth of certain native plants, like maple trees, triggering succession and disrupting turtle microhabitats.  In stark contrast to what perfect turtle habitat should look like – low-lying vegetation, soft wet soil and plenty of sun exposure – some of the conservation easements we visited were grown over with tall grasses, invasive trees and woody thickets.  The disappearance of traditional or prehistoric grazers (bison, elk and mastodon) means that these turtles’ best hope is habitat protection and controlled grazing by farm animals like cows, goats and sheep, combined with the eradication of invasive species.  And since 95% of bog turtle habitat lies within private properties, landowner incentives and active management are crucial to bog turtle recovery efforts.

Conservation easement boundary indicator issued by the USDA on the first private property we visited.

Ideal nesting habitat for bog turtles consists of low-lying tussocks of grass, supported by a bed of soft mud.

Jake picking his way through cattails, ferns, sedges, rose bushes and skunk cabbage – a textbook example of overrun habitat.

In our conversations with Jason and Brandon, it became rapidly apparent that not only are bog turtles highly conservation-reliant, but our main tool for protection is the USDA Wetlands Reserve Program.  This program is critical to providing the funding to eradicate invasive plants, manage herds of grazers and protect and restore wetland hydrology in dozens of wetlands throughout Pennsylvania that are critical to the turtle’s survival.

We were lucky enough to find turtle tracks on this visit, but if we transition towards and strengthen voluntary active management measures to rehabilitate this conservation-reliant species’ habitat, maybe we’ll actually see some turtles next time we visit these swamps.

Bog turtle tracks, but no bog turtles this time around!

Jason Tesauro is the owner of Jason Tesauro Consulting; Brandon Ruhe is a co-founder of MACHAC and Aqua-Terra Environmental Ltd.  Both are United States Fish and Wildlife Service Qualified Bog Turtle Surveyors.

Co-authored with Jake Li and Tim Male.

DT Crouse, LA Mehrhoff, MJ Parkin, DR Elam, LY Chen. 2002. Endangered Species Recovery and the SCB Report: A U.S. Fish and Wildlife Service Perspective. Ecological Applications 12: 719-723.

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Trade offs in time and costs in developing Habitat Conservation Plans (HCPs)

Co-authored with Jake Li

The USFWS has approved more than 500 Habitat Conservation Plans, allowing developers, private landowners and state and local governments to move forward with projects that may harm endangered species.  The Plans and the process for approving them are widely criticized for many things, but in particular because they take so long to finalize.  For example plans in Yolo County, California and for the Sonoran desert of Pima County, Arizona took more than eight years to complete.

It’s unclear why the U.S. Fish and Wildlife Service (USFWS) doesn’t offer more transparent choices to developers when initiating development of an HCP.

For example, at the time an applicant walks in the door of a USFWS office, there is a certain amount of information known about the site where a development will occur and the likely impacts of that development – that information represents the ‘best available science’ at the time.  In most cases that information provides the agency with very little certainty about the endangered species that will be impacted, the magnitude and significance of those impacts, and the options for avoiding, minimizing and mitigating those impacts.  Nevertheless, some information is available to agencies and they could move forward with the applicant in developing an HCP.  The likely outcome would be very high mitigation requirements based on estimates for the most robust characterization of the population of species that might be present on the development site.  The USFWS policy handbook on this subject already makes allowance for this approach by saying that where “the applicant insists consultation be completed without the data or analyses requested…” USFWS is expected to give ‘the species the benefit of the doubt.” The applicant, in securing a quicker answer would accept a trade off of mitigation costs that better (but as yet unavailable) science could reduce.

In contrast, an applicant who works with the USFWS to exhaustively document the wildlife on and near the development site and to work with the USFWS to try to minimize and avoid impacts to that wildlife may typically have a much lower mitigation cost, but will end up funding expensive research and perhaps more importantly, waiting years for the results of the research they fund.

If time is the most important factor for a developer of a project seeking an HCP from the U.S. Fish and Wildlife Service, it’s not clear why they shouldn’t have more choices to pursue a quicker, but more expensive route to a finalized HCP.  USFWS could offer such an outcome without resulting in worse outcomes for wildlife and perhaps even with better results, since applicants will sometimes be paying for beneficial wildlife activities that ‘not yet available’ science would have shown were not required.

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At Midway Atoll, Birds Take a Hard Hit from the Tsunami

The stories pouring out of Japan paint a heartbreaking picture of the enormous toll last week’s earthquake and tsunami have taken on the country and its people, and of the long road to recovery ahead.  That same violent earthquake also generated another tsunami that swept across the Pacific Ocean and eventually washed over a set of coral islands in the Hawaiian archipelago.  Now, as the process of rescue and recovery continues in Japan, a different sort of disaster response has begun about 2,000 miles away.

Midway Atoll, established as a national wildlife refuge in 1988, is usually a thriving home to endangered Hawaiian monk seals, threatened green sea turtles, 21 species of seabirds, and a diverse array of other wildlife.  Today, refuge staff are sifting through the damage, counting carcasses and rescuing those animals that made it through.  It is estimated that tens of thousands of Laysan albatross chicks nesting on the islands were killed when they were carried off with the water, and 1,000 of the adult and subadult birds are dead.  Others survived, but they are injured or stuck under toppled vegetation and debris.  Thousands of Bonin petrels, which nest in burrows, were likely buried under the sand.

While the losses are great, Midway Atoll has certainly rebounded from tsunamis and other natural disasters in the past.  Many plants and animals have adapted to such disturbances.  So, why should we worry now?  Because this time, a tsunami isn’t the only problem.  Ocean acidification, invasive species, and marine debris are ongoing threats.  And sea-level rise could put much of the habitat under water.  Together, these stresses could push the ecosystem beyond its ability to recover.

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Table with examples of the U.S. Fish and Wildlife's recovery priority system

Recovery priorities for endangered species explained

The U.S. Fish and Wildlife Service has a complicated job in managing the conservation and recovery of more than 1,300 U.S. species protected under the Endangered Species Act.  In 1983, they established a priority system, to help them make choices on where to invest in developing recovery plans and implementing those plans – and to provide transparency to the public on those choices.

The system has 36 ranks for wildlife and plant species and uses the following nested variables to sort through species:

  • Degree of threat: Species are assigned to either a high, moderate or low degree of threat.  High means that extinction is almost certain in the immediate future because of population decline or habitat destruction.  ‘Moderate’ means extinction is not immediately likely to occur if investments in recovery are temporarily delayed.
  • Recovery potential: Species are assigned one of two categories – high or low recovery potential.  ‘High’ potential for success are species with threats and biology well-understood and recovery actions that are either not intensive or are actions that have been used before and have a high probability of success.
  • Taxonomy:  The most genetically distinct species receive a higher priority.
  • Conflict:  Because of 1982 amendments to the ESA, species which are in conflict with construction, development or other economic activities are meant to be a higher priority for the agency.

The system works like this:

Table with examples of the U.S. Fish and Wildlife's recovery priority system

In practice, there is little evidence that the U.S. Fish and Wildlife Service uses this system in deciding which recovery plans to implement and which actions to fund.  This 2008 report to Congress provides the latest information on the priority ranks of each species.  In 2005, the Government Accountability Office concluded in a report that the U.S. Fish and Wildlife Service does not have a process to measure the extent to which funding is aligned with this and other priority systems.

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Endangered Species on the Bus?

Endangered Species on the Bus?

Photo of one of the "Endanger Buses" in San FranciscoSide view of an "Endanger Bus" in San Francisco

Do you mind sharing your seat with a brown pelican?  Don’t worry, you won’t have to.  These endangered species are on the outside of the bus.  Endangered Species is an art project on San Francisco’s public buses. Images of endangered species are wrapped around the buses with information about the species on the back of the bus.

The project was the idea of artist Todd Gilens, inspired by the visual elements of everyday urban life.  “Buses are so assaulted by advertising, it’s as if our transit system is not our own. But whose environment is it? How can we best look after the places we live?” questioned Gilens.  “Public transit is about pooling and sharing resources. Bringing the bus together with local ecosystems and vulnerable animal species was a natural fit once I started to think about it that way.”

The Endangerbuses will be prowling the streets of San Francisco from January to April 2011, dispatched to different routes each day.  You can follow the Endangerbus adventure on Twitter at #endangerbus.  If you visit or live in the San Francisco area, post your pictures on Flickr tagged with endangerbus.

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dotWild is the blog of scientists and policy experts at Defenders of Wildlife, a national, nonprofit membership organization dedicated to the protection of all native animals and plants in their natural communities.