Over the last few posts, I’ve outlined the situation facing several owl species in decline- in general, although there are other factors with influence, the major culprits are habitat change and habitat loss. Since human populations often value the same areas used by owls, sometimes more for what they could be rather than for what they are, there is bound to be conflict between both groups. But there are also ways that we can contribute directly to owl conservation and make things a bit easier for our feathered friends.
Many management and conservation organizations want your help in locating owls in your community:
-The Urban Bird Foundation is looking for Burrowing Owls in California
-The British Trust for Ornithology can always use help with bird surveys
-The Pennsylvania Barn Owl Conservation Initiative wants to know where Barn Owls are hanging out
-As I’ve mentioned before, eBird collects information on bird sightings from all over and then uses this information to assess population trends- whether you see an owl or hummingbird or something in between, they would love your input
For those of you looking to get more involved in owl conservation, there are opportunities to volunteer at office tasks and educational events (check out Conservation Northwest), helping with owl reintroduction programs (Burrowing Owl Conservation Society of BC, Wild At Heart), and assisting injured owls (Owl Foundation and the Avian Conservation Center).
You can also play a part in ensuring that owls have the habitat they need to survive:
-The Center for Biological Diversity has a current petition to make sure that Forest Service plans to manage the Coronado National Forest provide adequate protection for Mexican Spotted Owls and other species living in the forest (they would like you to sign the petition by March 6)
-Give owls a chance to share your space by putting up a nesting box and managing your property to provide the habitat they are looking for
Barn Owls: nest box design from the PA Barn Owl Conservation Initiative, description of habitat needs from the Barn Owl Conservation Network
Barred Owls: nest box design from the PA Barn Owl Conservation Initiative, general information on living with owls from the Missouri Department of Conservation
Burrowing Owls: learn how to attract them from the FL Fish & Wildlife Conservation Commission
Screech Owls: nest box design from the Owl Foundation
Owls are majestic animals and skilled hunters. Many species also seem to do reasonably well within human landscapes provided we take their needs into account as well as our own. By protecting vital habitat and finding novel ways to coexist, we can help those species that are in decline to recover, but it will take effort from all of us. Hopefully the ideas here will get you started, and I’ve probably just scratched the surface.
In my last post, I catalogued a variety of issues facing owls in different places around the world- while a lot of that was focused on the northern spotted owl, the issue of habitat loss is pretty well universal. I had expected that most of the recent literature on owl conservation would investigate complex relationships between prey species and predator numbers or assess the success of different conservation programs, but a lot of what I found was mainly about diet or habitat selection, which suggests to me that we still have some large gaps in our ecological knowledge of many owl species (there were also many papers recounting the westward spread of barred owls as scientists compared theories for the cause- after a while, it felt like I was reading the same thing over and over…).
The good news is that there were some signs that conservation efforts and general awareness of ecological relationships have given some owl species the space they need to recover or remain stable. An assessment of owl species across Europe found that only 4 of 15 species had declined between 1990 and 2000, perhaps in part because 8 of the owl species have action plans to facilitate conservation (Burfield 2008). Further research into the distribution and habitat needs of the cloud-forest screech owl (Megascops marshalli) suggests that a larger population exists over a larger range than had previously been thought, which means that this species may have good long-term prospects if deforestation throughout its range can be controlled (Herzog et al. 2009). And several researchers are working with farmers in Kenya to both better understand the ecology of the Mackinders eagle owl (Bubo capensis mackinderi) and remove the traditional view of owls as evil omens (Ogada 2008).
And several studies concluded that there are ways to help burrowing owl populations. Since these owls depend on burrows created by other animals and seem to prefer active prairie dog colonies with less shrubby vegetation (the better to see predators in…), we could protect a variety of species by focusing on the colonies themselves (Lantz et al. 2007). In those areas without prairie dog colonies, artificial burrows are a viable option- not only do they last longer than abandoned colony burrows and give researchers the chance to set up cameras for close observation of nesting owls, but they also can be permanently marked in areas of regular mowing and road maintenance so that humans steer clear of the nests (Catlin & Rosenberg 2006).
Cactus Ferruginous PgymyOwl populations continue to decline
The problem is that some of the species I mentioned previously as being in trouble seem to be continuing down that slope. A study of the cactus ferruginous pygmy-owl in northern Mexico found that the population had declined by 37% percent between 2000 and 2004 (Flesch & Steidl 2006). Not only is that a problem for the local population, but it also means that there are fewer owls who might range farther north into Arizona and join the tiny population up there. Continued competition with the barred owl means that the northern spotted owl is no closer to recovery despite changes in logging practices- according to the USFWS, data from 2009 indicates that the species continued to lose 2.9% of its population per year (News Release, Pacific Regional Office, September 10, 2013). Given the implications of that decline, the USFWS has started removing barred owls from several locations in Washington, Oregon, and California– 26 had been removed from Hoopa Valley Indian Reservation by the middle of December- and the plan is to continue for 6 years. Researchers will monitor the response of spotted owls to this program in an attempt to determine if the program should be expanded. This is a controversial issue- there is certainly precedent for removing problems animals to protect a species in trouble (for example, targeting specific sea lions to protect troubled salmon stocks), but there is also concern that this measure results from the high-profile nature of the spotted owl issue (for example, there is no plan to remove crows, ravens, and Stellar’s Jays which eat the eggs and nestlings of the even more at-risk Marbled Murrelet population within the same spotted owl habitat [Livesey 2010]).
There are both bright spots and dark prospects for owl species around the world. It’s true that things look rather gloomy for some species, but we are much more aware of the needs of different species now. At the same time, researchers and officials are trying creative solutions to owl problems. They certainly cannot do it by themselves, however, so I’m pretty sure there are ways we can all pitch in and help. For my next post, I’ll investigate the options we all have for contributing to owl conservation.
Works cited:
Burfield, IJ.2008. The conservation status and trends of raptors and owls in Europe. Ambio 37: 401-407.
Catlin, DH and DK Rosenberg. 2006. Nest destruction associated with mortality and dispersal of burrowing owls in the Imperial Valley, California. The Southwest Naturalist 51: 406-409.
Flesch, AD and RJ Steidl. 2006. Population trends and implications for monitoring cactus ferruginous pygmy owls in northern Mexico. The Journal of Wildlife Management 70: 867-871.
Herzog, SK, Ewing, SR, Evans, KL, Maccormick, A, Valqui, T, Bryce, R, Kessler, M, and R MacLeod. 2009. Vocalizations, distribution, and ecology of the cloud-forest screech owl (Megascops marshalli). The Wilson Journal of Ornithology 121: 240-252.
Lantz, SJ, Conway, CJ, and SH Anderson. 2007. Multiscale habitat selection by burrowing owls in black-tailed prairie dog colonies. The Journal of Wildlife Management 71: 2664-2672.
Livezey, KB. 2010. Killing barred owls to help spotted owls I: a global perspective. Northwestern Naturalist 91: 107-133.
Ogada, D. 2008. Rural culture and the conservation of Mackinders eagle owl (Bubo capensis mackinderi) in Kenya. Journal of Avian Medicine and Surgery 22: 158-160.
In deciding to focus on owls for this month’s posts, I clearly had forgotten about one of the biggest debates over timber harvesting- the northern spotted owl (Strix occidentalis caurina) gained lots of publicity as a bone of contention in the discussion of what to do with old-growth forest in the Pacific Northwest.
As birds that depend upon old (meaning more than 150 years) forest for both roosting and nesting, northern spotted owls are very sensitive to habitat loss. And the debate over what our priorities are with regard to management of these forests was very vocal starting in the late 1970s (Noon & McKelvey 1996). These are decisions with wide-ranging impacts, both for a bird whose total population in California, Oregon, and Washington was estimated to be between 4000 and 6000 animals by 1987 (Simberloff 1987), and for the economics of the region where some of the land in question was valued at $4,000 an acre. Additionally, other species, such as northern flying squirrels, red tree voles, and Vaux’s swift, require these same habitat conditions, which made spotted owls something of a poster child for the entire old-growth ecosystem. I’m not going to recount the entire saga step by step here (see Noon & McKelvey 1996 below for more details), but there was a lot going on.
As it turns out, spotted owls are threatened by more than just habitat loss and small population size (although these are both important issues). They are also at risk from a fellow owl who has been expanding into their territory for several decades. Barred owls (Strix varia) were historically present in eastern North America, but have been spreading west since at least the 1940s (Dark et al. 1998). Barred owls are similar in size and appearance to spotted owls, but they are more aggressive and can displace spotted owls from their territories. More importantly, barred owls and spotted owls can produce fertile hybrids (Hamer et al. 1994). Why is it so important that these two species can hybridize? Well, there are a couple of issues here: to begin with, there is dilution of a species’ genome when one species dominate the genes of the other (for example, these owl hybrids had white bands very similar to barred owls, rather than looking like a combination of the two); additionally, the hybrids observed by Hamer et al. successfully bred with barred owls, rather than spotted owls, meaning that those offspring were lost from the spotted owl population; and the big problem tends to come down to conservation efforts- even though northern spotted owls are listed as threatened under the Endangered Species Act, there is no protection within the legislation for hybrids- if enough barred owls interbreed with spotted owls, there may be no grounds to continue protecting the species.
Burrowing owls are generally dependent on other animals to construct the burrows they use for nesting.
It took me a while to work my way through the various studies on spotted owls (the Mexican spotted owl is also threatened, the California spotted owl is a species of concern…), but when I reached the other side, I discovered an entire suite of literature on other owl species in decline but without the same level of publicity. With the exception of Florida (although they have other issues there), burrowing owls (Athene cunicularia) are in decline across much of their range (and listed as endangered in Canada) due to limited nest sites and reproductive success (Desmond et al. 2000). As prairie dog colonies have disappeared, burrowing owls have found themselves without suitable burrows for nesting and more exposed to predators. In Florida where the owls create their own burrows, they have generally done well in the partially developed areas humans made by filling in wetlands- however, when the percent of developed land goes above 60% in a given area, owls experience reduced breeding success due to human disturbance, difficulty burrowing under lawn sod, and burrow collapse during mowing operations (Millsap & Bear 2000). Cactus ferruginous pygmy-owls (Glaucidium brasilianum) in Arizona were listed as endangered in 1997 following decades of decline (Johnson et al. 2003). When researchers looked back through 100 years of sighting records, they realized that the decline became noticeable starting in the 1920s, a time-scale that aligns suspiciously well with the major water reclamation projects carried out between 1902 (The National Irrigation Act) and the 1930s- the loss of cottonwood habitat as rivers were turned into lakes is a likely cause of the owl’s decline. Farther afield, in the last two decades of the 20th century eagle owls (Bubo bubo) in Italy experienced high rates of mortality from electrocution when individuals tried to land on power line pylons which have become ever more of a presence in the countryside (Sergio et al. 2004).
So owls around the world have certainly had their share of problems during the 20th century, but there has also been a lot of work to better understand owl ecology and address some of the causes of population decline. In my next post I’ll take a look at how things have progressed over the last 15 years or so and how researchers feel about their future prospects.
Works cited:
Dark, SJ, Gutierrez, RJ, and GI Gould, Jr. 1998. The barred owl (Strix varia) invasion in California. The Auk 115: 50-56.
Desmond, MJ, Savidge, JA, and KM Eskridge. 2000. Correlations between burrowing owl and black-tailed prairie dog declines: a 7-year analysis. The Journal of Wildlife Management 64: 1067-1075.
Hamer, TE, Forsman, ED, Fuchs, AD, and ML Walters. 1994. Hybridization between barred and spotted owls. The Auk 111: 487-492.
Johnson, RR, Cartron, JE, Haight, LT, Duncan, RB, and KJ Kingsley. 2003. Cactus ferruginous pygmy-owls in Arizona, 1872-1971. The Southwestern Naturalist 48: 389-401.
Millsap, BA and C Bear. 2000. Density and reproduction of burrowing owls along and urban development gradient. The Journal of Wildlife Management 64: 33-41.
Noon, BR and KS McKelvey. 1996. Management of the spotted owl: a case history in conservation biology. Annual Review of Ecology and Systematics 27: 135-162.
Sergio, F, Marchesi, L, Pedrini, P, Ferrer, M, and V Penteriani. 2004. Electrocution alters the distribution and density of a top predator, the eagle owl Bubo Bubo. Journal of Applied Ecology 41: 836-845.
Simberloff, D. 1987. The spotted owl fracas: mixing academic, applied, and political ecology. Ecology 68: 766-772.
I spend a lot of my time in an urban area with lights on every corner and sirens as my nightly serenade, but I have lived in areas where I could listen to owls calling to each other in the darkness. I was reminded of that fact a few days ago while looking at specimens in an ornithology lab- although the songbirds were pretty, I kept going back to the owls. (And the screech-owl on campus last week was pretty exciting, too.) I don’t know very much, however, about owl biology, conservation, or population status (or for that matter, how to identify more than a few species), so it seems right to add a new goal to my current pursuit of knowledge.
I love the faces of barn owls!
This month I will be exploring the condition of owls around the world (depending on what I find, there may be particular attention to barn and barred owls, my two favorites)- I imagine that they share many of the issues facing birds in general. It is also possible that, as carnivores, they have additional or different problems. And I come to the table with very little background knowledge, aside from knowing that they are nocturnal, largely meat-eating, and have sharpened eyesight and hearing for detecting prey. (From contact with rehabilitated owls, I think that they sometimes enjoy flying as closely to your head as possible, but that seems beside the point…) I believe that some owl populations in more northern locations are closely linked to the rise and fall of prey populations, and I had heard something about a decline in nesting places for barn owls as old buildings were demolished and church steeples covered with mesh to keep them out, but that about exhausts my knowledge of owl ecology.
My hope is that I can learn quite a bit over the next few weeks about how owls are faring in the world today and their prospects for the future. It may be that they are all doing quite well, which would be wonderful, but it may be that they could use a leg (or a wing) up. So if you enjoy looking at and listening to owls as much as I do, then this month’s posts should be right up your alley.
As I mentioned in my last few posts, harbor seals (and a wide variety of sea creatures) seem to challenged most by competition with humans (for food and space), pollution, and disease. Although several harbor seal populations appear stable or increasing, there is still concern about seals in Alaska, Scotland, and other locations. Given human dependence on the world’s oceans, we can expect that competition between seals and people will continue into the future. The same can probably be said for pollution and outbreaks of disease. But I think that there are things we can do to lessen the severity of these problems for both harbor seals and those marine mammal species with less-promising population trends.
Common or harbor seal in Europe
Steps to lessen the tension between humans and seals:
- Jansen et al. (2010) suggested that large ships in Alaska remain at least 500m from harbor seals to avoid disturbing them and forcing young pups to spend extra time in cold water- that’s probably a good rule of thumb for boats and people in general since harbor seals seem particularly sensitive to human presence.
- Since harbor seals like beaches just as much as we do, there are bound to be issues like that of Children’s Pool in La Jolla, CA which is both a harbor seal pupping site and a beach used by people. The city of San Diego is in the process of trying to create a plan which both protects seals from harassment, especially during pupping season, and ensures resident-access to the sheltered cove as well (to judge from the discussions on this issue I found by a variety of pro- and anti-beach closure groups, this is not an easy task). The idea of seasonal shared-use of beach areas may be helpful in mitigating seal-human conflicts around the world.
- It is likely that seals will continue to eat the same fish species we use for food, sometimes causing damage and lost revenue to the fishing and aquaculture industries. We can perhaps lessen the impact of these animals by being willing to compensate fishermen and aquaculturists for the damages, similar to the way in which herders are sometimes compensated for the loss of livestock to leopards and lions.
- Greater access to information about marine mammals and the roles they fill could be helpful in creating more positive attitudes toward them- you can volunteer with MarineBio on a variety of informational projects aimed at both scientists and the public, and the Virginia Aquarium and Marine Science Center (and other similar institutions) has volunteers who act as public educators.
Cleaning up the oceans:
- A variety of organizations, such as the Marine Conservation Society in the UK, have regular beach clean-up events which can benefit all beach-goers.
- For those of you who use facial cleaners or other products with microbeads, there is a movement to get manufacturers to stop using petroleum-based plastic microbeads which go directly through water treatment and into our rivers and oceans where they are ingested by small animals and work their way up the food chain. Check out beatthemicrobead.org for more information- they even have an app to help you identify better products when shopping.
Helping individual animals:
- The New England Aquarium in Boston has volunteer positions for care of exhibit animals and marine animal rescue. (Many other Aquaria have marine animal rescue teams, so there may be one close to where you are.)
Work cited:
Jansen, JK, Boveng, PL, Dahle, SP, and JL Bengtson. 2010. Reaction of harbor seals to cruise ships. Journal of Wildlife Management 74: 1186-1194.
In my last post, I explored the large issues facing harbor seals throughout the 20th century, including competition with humans, pollution, and disease. In looking at the last decade or so, these themes continue to be important but I think that they have become more indirect in nature in some cases. Although seals still eat salmon and other valuable fish and there are regular chemical spills and disease events, there are other smaller challenges that can add up over time. And there are cases where seals and humans seem to be doing well together.
Common or harbor seal in Europe
Certainly the US Marine Mammal Protection Act and similar legislation around the world has made a difference for harbor seal populations– Gilbert et al. (2005) estimated that the number of harbor seals along the Maine coast increased at over 6% per year once hunting ended, and the 2004 census of harbor seals in California concluded that populations there were stable or increasing (Lowry et al. 2008). But there are still concerns about declining numbers in Glacier Bay National Park, Alaska (Womble et al. 2010) and the ~13% yearly decline witnessed in the Orkney Islands, UK between 2001 and 2010 (Hanson et al. 2013).
Living alongside humans has exposed harbor seals to a variety of small disturbances which may have negative consequences. Even when we are careful about handling organochlorines, other materials discharged into our waterways (which usually find the sea at some point) are causing health problems for a host of marine mammals. Among the bacteria found in harbor seal pups on Smith Island, Washington was salmonella which may have been introduced by agricultural run-off or sewage (Huggins et al. 2013). (And antibiotic-resistant bacteria have even been found in northern elephant seals- Stoddard et al. 2005.) Of the mass mortality events seen in marine mammals (an estimated 7-8 per year), harmful algal blooms seem to be increasing (Gulland & Hall 2007), possibly because of compounds in surface run-off or due to climate change. Why should we be worried about seal infections and algal blooms? Drug-resistant bacteria doesn’t bode well for anyone, especially if it is infectious in multiple species, and algal blooms can kill the seafood we depend on and make us sick as well.
These harbor seals enjoy relaxing on the beach as much as we do.
High levels of human activity can also be a problem for marine mammals. Because harbor seals haul out on land, versus ice, their favorite resting areas are sometimes our favorites, too. In areas along the West Coast with lots of people and noise, harbor seals spend more time in the water during the day and haul-out more often at night to avoid people (Acevedo-Gutierrez & Cendejas-Zarelli 2011). They also seem more sensitive to certain types of noise than other pinnipeds- unlike California sea lions who showed brief concern over the noise from Navy missile tests on San Nicolas Island, California, harbor seals usually left the area for at least 2 hours (Holst et al. 2011). (Northern elephant seals barely registered the noise levels, suggesting to me that elephant seals, like a 500-lb gorilla, sit pretty much wherever they want…) Harbor seals have also abandoned haul-out sites when levels of human presence became too great (Becker et al. 2009). Since human populations along the world’s coastline continue to grow, we can expect that harbor seals in some areas will find themselves pinched for beach space.
And expanding human travel has the potential to cause issues for harbor seals in more northern locations. The growing cruise industry in Alaska means that seals and cruise ships are increasingly using the same areas- a study in Disenchantment Bay found that harbor seals were likely to escape into the water when cruise ships came within 400 m, and that 90% of seals were in the water by the time ships reached the NOAA’s 91 m guideline for ship distance from marine mammals (Jansen et al. 2010). Why should it matter if harbor seals spend more time in the water? After all, they are marine mammals. In fjords like Disenchantment Bay, where glacial meltwater mixes with sea water, water temperature ranges from 3° C to 7° C. For young (less than 15 days old) harbor seal pups who are more sensitive to cold water, increasing the portion of their day spent in the water from 40% to 50% would mean that they needed an extra 4-10% of energy per day to keep warm and keep growing.
So, although harbor seal populations have benefitted from protective legislation, there are still a number of ways in which human activity directly and indirectly negatively impacts this species. And many of the issues I’ve described in my posts apply to a wide variety of marine mammals around the world. In the same way that we were able to limit over-hunting of harbor seals, we can also help clean up their environment and lessen the consequences of living side by side with us. In my final post of the month, I’ll explore ways we can get directly involved in harbor seal, and general marine mammal, conservation efforts- goodness knows that healthier, more balanced ocean ecosystems are good for us as well.
Works cited:
Acevedo-Gutierrez, A and S Cendejas-Zarelli. 2011. Nocturnal haul-out patterns of harbor seals (Phoca vitulina) related to airborne noise levels in Bellingham, Washington, USA. Aquatic Mammals 37: 167-174.
Becker, BH, Press, DT, and SG Allen. 2009. Modeling the effects of El Nino, density-dependence, and disturbance on harbor seal (Phoca vitulina) counts in Drakes Estero, California: 1997-2007. Marine Mammal Science 25: 1-18.
Gilbert, JR, Waring, GT, Wynne, KM and N Guldager. 2005. Changes in abundance of harbor seals in Maine, 1981-2001. Marine Mammal Science 21: 519-535.
Gulland, FMD and AJ Hall. 2007. Is marine mammal health deteriorating? Trends in the global reporting of marine mammal disease. EcoHealth 4: 135-150.
Hanson, N, Thompson, D, Duck, Callan, Moss, S, and M Lonergan. 2013. Pup mortality in a rapidly declining harbour seal (Phoca vitulina) population. PLoS ONE 8: e80727.
Holst et al. 2011. Responses of pinnipeds to navy missile launches at San Nicolas Island, California. Aquatic Mammals 37: 139-150.
Huggins et al. 2013. Causes and patterns of harbor seal (Phoca vitulina) pup mortality at Smith Island, Washington, 2004-2010. Northwestern Naturalist 94: 198-208.
Jansen, JK, Boveng, PL, Dahle, SP, and JL Bengtson. 2010. Reaction of harbor seals to cruise ships. Journal of Wildlife Management 74: 1186-1194.
Lowry, MS, Carretta, JV, and KA Forney. 2008. Pacific harbor seal census in California during May-July 2002 and 2004. California Fish and Game 94: 180-193.
Stoddard, R, Gulland, FMD, Atwill, ER, Lawrence, J, Jang, S, and PA Conrad. 2005. Salmonella and Campylobacter spp. in northern elephant seals, California. Emerging Infectious Diseases 11: 1967-1969.
Womble, JN, Pendleton, GW, Mathews, EA, Blundell, GM, Bool, NM, and SM Gende. 2010. Harbor seal (Phoca vitulina richardii) decline continues in the rapidly changing landscape of Glacier Bay National Park, Alaska 1992-2008. Marine Mammal Science 26: 686-697.
A quick look at harbor seal population trends around the world suggests that there have been ups, downs, and even some unknowns- catastrophic crashes in one part of the world while numbers grew in another and scientists couldn’t determine the pattern in a third. This wide-spread species shows corresponding variation in population status, but three big themes seem to run through the scientific literature: competition with humans, pollution, and disease (and the number of studies looking at this third issue really surprised me).
Humans and harbor seals tend to clash due to the lure of salmon and other tasty fish. Prior to passage of the US Marine Mammal Protection Act in 1972, some states paid bounties for harbor seals because of concerns that they competed directly with fishermen for certain valuable species (Lelli et al. 2009)- an estimated 72,284-135,498 seals were killed in Massachusetts and Maine between 1888 and 1962. Those concerns continue today- in Saint John Harbour, New Brunswick, for example, harbor seal numbers appear to increase during the yearly alewife migration (Browne & Terhune 2003), while in the Cromarty Firth, Scotland, harbor seals were more often seen within the freshwater river system during salmon migration (Middlemas et al. 2006). And the spread of aquaculture has provided more opportunities for human-seal conflict- along the New England and Canadian Atlantic coast harbor seals have damaged fish cages and eaten farmed salmon (Jacobs & Terhune 2000). Given how much we depend on oceanic resources for food and concerns over fish stocks, it’s no wonder that we’re worried about competition with these animals. Through the early 1970s harbor seals were hunted along the Pacific and Atlantic coasts of North America and in Europe, but later legislation enacted by governments provided protection. The US Marine Mammal Protection Act states that populations of species such as harbor seals should be maintained at a level that allows them to remain a significant part of the ecosystem. Why should we continue to protect these seals if they are causing damage to aquaculture and taking fish we could use? Well, I think that there are (at least) two ways to respond to that. To begin with, I do think we have to ask ourselves whether we over-consume the resources around us and whether we could make do with less so that other species can continue get the resources they need to survive. The other element is the long-term impact of removing high-level consumers from any food chain- the effects can be bad for the entire system, including us. I found a study which suggested that our over-harvest of large whales in the Pacific led to a cascading decline in seals, sea lions, and even sea otters because killer whales turned to other food sources when whales become scarce (Springer et al. 2003). The loss of sea otters then meant that sea urchins could overgraze kelp beds with the result that abundance and diversity of total sea life declined. Ecosystems can be pretty complicated, and removing one piece from the web can cause the whole thing to unravel.
Water pollution also took its toll on harbor seal populations and in some cases prevented populations from recovering once they were granted legal protection. European populations in the North and Baltic Seas showed high levels of DDT and PCB contamination (Helander & Bignert 1992), both of which cause decreased reproductive success in mammals. These types of chemicals were also implicated in hormonal and metabolic problems found in dead grey and ringed seals in the Baltic (Bergman & Olsson 1986). This means that exposed animals may be less able to fend off future diseases. Why should we worry about organochlorines in seals? If you want to evaluate water quality, one of the best indicators is the health of animals living in that water- if seals are contaminated, it is likely their prey is as well, and that means that our prey is, too, as well as the water which cools us off on a hot day at the beach.
Disease appears to be a pretty big deal as well. And I will be honest that I did not expect to find so many references to this in the literature- seal pox, seals dying from influenza which appeared to originate in birds, a seal fever in Iceland- it was a little overwhelming. A phocine distemper virus killed roughly 60% of the harbor seals from Sweden to the eastern coast of the UK (and up into the Scottish Isles) in 1988 (Dietz et al. 1989), and a (possibly) second wave with lower mortality came through in 2002 (Thompson et al. 2005). Seals with higher levels of organochlorines were more likely to die from the virus, indicating that their immune systems may have been compromised by chemical contamination. These disease epidemics are worrying on several levels: to begin with, they severely reduce seal populations which makes these populations more vulnerable to extinction and can lead to loss of genetic diversity. They could also be a statement about the general health of the ecosystem- more disease outbreaks could mean bigger ecological problems. And it is also possible that humans can be directly impacted by animal diseases (think about H1N1 or rabies…), so healthy seals are probably a good thing for just about everyone.
Harbor seal populations have experienced large fluctuations around the world over the last 100-150 years. Although protection has helped some populations rebound, such as in New England, there are still concerns for other populations. The problems I’ve described here offer something of a long-term perspective, looking at harbor seals through the 20th century- it’s likely that there are other issues facing which have arisen in the last decade. For my next post, I’ll concentrate on recent trends in harbor seal populations and the outlook for the future.
Works cited:
Bergman, A and M Olsson. 1986. Pathology of Baltic grey seal and ringed seal females with special reference to adrenocortical hyperplasia: is environmental pollution the cause of a widely distributed disease syndrome? Proc. from the Symposium on the Seals in the Baltic and Eurasian Lakes, 1984-06-05-08. Finn. Game Res. No. 44: 47-62.
Browne, CL and JM Terhune. 2003. Harbor seal (Phoca vitulina, Linnaeus) abundance and fish migration in the Saint John Harbour. Northeastern Naturalist 10: 131-140.
Dietz, R, Heide-Jorgensen, M-P, and T Harkonen. 1989. Mass deaths of harbor seals (Phoca vitulina) in Europe. Ambio 18: 258-264.
Helander, B and A Bignert. 1992. Harbor seal (Phoca vitulina) on the Swedish Baltic coast: population trends and reproduction. Ambio 21: 504-510.
Jacobs, SR and JM Terhune. 2000. Harbor seal (Phoca vitulina) numbers along the New Brunswick coast of the Bay of Fundy in autumn in relation to aquaculture. Northeastern Naturalist 7: 289-296.
Lelli, B, Harris, DE, and A-M Aboueissa. 2009. Seal bounties in Maine and Massachusetts, 1888 to 1962. Northeastern Naturalist 16: 239-254.
Middlemas, SJ, Barton, TR, Armstrong, JD and PM Thompson. 2006. Functional and aggregative responses of harbour seals to changes in salmonid abundance. Proceedings: Biological Sciences 273: 193-198.
Springer, AM, Estes, JA, van Vliet, GB, Williams, TM, Doak, DF, Danner, EM, Forney, KA and B Pfister. 2003. Sequential megafaunal collapse in the North Pacific Ocean: an ongoing legacy of industrial whaling? PNAS 100: 12223-12228.
Thompson, D, Lonergan, M, and C Duck. 2005. Population dynamics of harbour seals Phoca vitulina in England: monitoring growth and catastrophic declines. Journal of Applied Ecology 42: 638-648.
As I write this, snow is falling outside on a cold, wintery New England day. Beautiful to look at and fun to play in when all bundled up, but it’s nice to know that I can come in from the cold at any time. I am amazed by mammals and birds that survive in environments dominated by snow and ice- I can’t imagine prospering in a habitat where cold is an ever-present danger, and that goes double for aquatic mammals and birds who spend so much of their time immersed in a medium that can drain the heat from their bodies even faster than air.
In honor of the season and the ice-covered water rushing past my window which will eventually find the Atlantic, I’ll be looking at the situation of one of New England’s oceanic mammals, the harbor seal (Phoca vitulina). Pretty much everything that I know about this species (and that’s not much) comes from seeing it at the New England Aquarium: cute face, lives in water (obviously), present off the New England coast throughout the 19th and 20th centuries. Beyond that I can imagine that they share some of the same problems facing other high-latitude aquatic mammals such as global warming, water quality, and competition with humans for certain resources. I’m sure there is much more to their story, so I’m going to spend the next few weeks getting a better sense of their present condition, past issues that have impacted these seals, and their prognosis for the future. Hopefully I’ll also uncover some ways for us to get directly involved in the conservation of this species and their compatriots in a cold, watery world.
A chilly topic, but hopefully only in terms of climate and not future prospects.
Over the past few weeks, I’ve been looking at the issue of habitat fragmentation in respect to how it divides populations and presents barriers to animal movement which can limit reproductive success and gene flow. When I started gathering information on how to combat and mitigate habitat fragmentation, most of the resources I came across were focused on assessing degrees of fragmentation and looking at large scale policies- while that’s important for broader connectivity, it doesn’t necessarily translate into actions we can take on a regular basis. I took two lessons from this: A) we need to think outside the box for small scale options, and B) public policy will play a big role in how our landscape is connected in the future, so we need to make sure we tell those making the policies what we want. There are quite a few states and watershed areas (California, Washington, Colorado, the Rappahannock, etc.) with organizations specifically working to make habitat connectivity a general priority, so, if you do a little digging, you may find a local group you can support.
Here’s what I’ve managed to cobble together from a variety of sources as suggestions for limiting and reversing habitat fragmentation:
For animals that swim:
Culverts can increase water flow and their smooth sides don’t provide much to grasp- using bottomless versions gives animals protection from flow and better substrate as they cross.
In addition to the problems caused by canals and spoil banks, we create fragmentation when we force a boat through marshy areas- once we’ve loosened up the vegetation, tidal and wave action can cause erosion- or drag our anchor through a bed of seagrass. Sometimes the best option is to go around something.
Along a number of rivers, the dams which had originally been constructed to power mills and other machinery are no longer used, so there are organizations working to restore river access for fish species that needs to migrate upstream- check out Maine Audubon for some examples (plus they have a blog on habitat fragmentation).
Even within an urban environment, we can create habitat corridors that allow animals to move through the landscape
For animals that climb trees and fly:
Part of the challenge for these organisms is exposure to predators and to us when they cross open spaces, so keeping canopy gaps to a minimum can be helpful here- that means trees that are tall and close enough together for birds and gliding mammals so that they don’t have to use the ground.
If we want to keep insect pollinators moving from patch to patch and providing us with important ecosystem services, we need to ensure they have enough wildflower cover running along bare areas, otherwise they may just stay in one location (and the same is probably true for seed dispersers).
For animals that spend their time on the ground:
One of the biggest dangers here is crossing the road- I think that means that we need to be especially careful when we see signs indicating we’re in a wildlife crossing area (and we can help them across, too- salamander crossing guards are always appreciated in the spring!), and we need to create other options, like elevated crossings, so that animals don’t have to set foot on pavement to get across a road.
For animals in general:
The National Wildlife Federation has suggestions for turning whatever backyard/patio/road frontage area you have into better wildlife habitat (although you might not think of this as connecting habitat, for those species who now share our space with us, it can make a huge difference). They also have a document on the issue of urban sprawl that you may want to check out.
I’ve just scratched the surface here in terms of what we can do to lessen habitat fragmentation- if there is a species that you care about, learn about what that animal needs to survive and how much it needs to move around. With a little creativity you can start making changes in your community to help that species.
In my last post, I looked at the consequences of habitat fragmentation when we build roads or dams or other physical structures- we construct barriers that are useful to us, but not so helpful to the plant and animal populations we isolate. And sometimes we create obstacles to movement even when we think we’re making small changes. One of the most important elements of habitat fragmentation is what we call the matrix, the environment directly around the fragments- when we replace habitat with roads, it’s pretty obvious that we’ve drastically altered the environment and created a hostile matrix; but changes don’t have to be that profound to have a big impact.
The yellow flowers are in a tilled field- pretty to look at, but not really offering a lot to wildlife
Think about driving through an area filled with farms- we might see pastures, tilled fields, streams bordered by thick vegetation, or forest patches. While it might look like there is plenty of space for plants and animals of all kinds and no shortage of vegetation, the reality is that many species do not thrive in habitats that have been manipulated by humans. But don’t the fields provide food sources and vegetative cover? Well, it depends on what you mean by that. Certainly we gain food from the fields and pastures, and it’s true that animals aren’t as visually exposed on farmland as on, say, tarmac, but we’ve replaced the natural environment with something considerably more artificial, leaving some species out in the cold. A study on common toads in Europe, for example, found that toads were able to move much more easily through woodland and meadows than through cropland (Janin et al. 2009)- intensive agriculture creates environments with less water content and more chemicals, neither of which is good for amphibians. Researchers in the Czech Republic found that carnivores were much more likely to stay in the long grasses and shrubs bordering hayfields than to venture into the fields themselves (Salek et al. 2009)- this could be because they feel more at risk in the fields or because the prey they seek prefers more vegetative cover. This situation applies to forests as well- more species of longhorn beetle were found in natural forest when compared with cedar planted forests in Japan (Yamaura et al. 2011), and arboreal mammals in Australia did not disperse through pine plantations above a certain distance even though there were still tall trees to climb ( Lancaster et al. 2011). Either way the message is clear: all vegetation types are not equal. As a result of replacing forest with meadow or grassland with subdivision or hedgerows (originally left in place to mark the edges of fields) with more cropland, species that depend on the microclimates created within more complex habitat find themselves encircled or even excluded by the matrix- in the UK, for example, hedgehog numbers have declined systematically as large-scale agriculture consolidated fields and removed hedgerows (Robinson & Sutherland 2002). Researchers have also found that pollination can be negatively impacted by habitat fragmentation, for example when pollinating insects must cross large fields of corn to get to the next patch (Van Geert et al. 2010).
These birds nest on what once was a much larger island- as you can see, tidal and storm erosion are eating away at their habitat, a bit at a time
We’re fragmenting aquatic systems as well, which is something that I have seen quite a bit of here in Louisiana. We may remove aquatic vegetation when boats and their propellers hit the bottom- you might say that, since it’s in water, the fish or crustaceans can simply swim to the next patch, but remember that entering open water may be a very risky undertaking if predators are near. To get to some of the islands I work on, we follow dredged canals created to facilitate shipping- it breaks up the marsh, leading to altered water flows which can increase erosion (Wilson et al. 2007), and once again open water can be a real problem to cross. Sometimes we also pile the dredged material on either side of the canals, creating earthen barriers that aquatic organisms can’t cross (Haas et al. 2004). Animals left out on the islands of marsh may find themselves increasingly isolated, especially as sea levels rise. I find it sad to think that we’re creating something of a no-win situation for these populations- not only are we directly using some of their previous habitat, but our activities are also steadily limiting their options for responding to change.
I found these two raccoons sleeping in the sun on a pipeline sign in the canal- I know they can swim back to dry land, but I also know that there are bigger creatures than raccoons hanging out in the canal
There are different ways that we create fragmented habitat- sometimes it’s a clear, hard line, and sometimes the new habitat might look similar to what was there before but be fundamentally different underneath the surface. Luckily, there are also many studies looking into what can be done to mitigate isolation and keep these animals and plants moving throughout the landscape- for my final post of the month, I’ll have a range of suggestions for how you can keep the lanes of travel open.
Works cited:
Haas, HL, Rose, KA, Fry, B, Minello, TJ, and LP Rozas. 2004. Brown shrimp on the edge: linking habitat to survival using an individual-based simulation model. Ecological Applications 14: 1232-1247.
Janin, A, Lena, J-P, Ray, N, Delacourt, C, Allemand, P and P Joly. 2009. Assessing landscape connectivity with calibrated cost-distance modelling: predicting common toad distribution in a context of spreading agriculture. Journal of Applied Ecology 46: 833-841.
Lancaster, ML, Taylor, AC, Cooper, SJB, and SM Carthew. 2011. Limited ecological connectivity of an arboreal marsupial across a forest/plantation landscape despite apparent resilience to fragmentation. Molecular Ecology 20: 2258-2271.
Robinson, RA and WJ Sutherland. 2002. Post-war changes in arable farming and biodiversity in Great Britain. Journal of Applied Ecology 39: 157-176.
Salek, M, Kreisinger, J, Sedlacek, F, and T Albrecht. Corridor vs. hayfield matrix use by mammalian predators in an agricultural landscape. Agriculture, Ecosystems and Environment 134: 8-13.
Van Geert, A, Van Rossum, F, and L Triest. 2010. Do linear landscape elements in farmland act as biological corridors for pollen dispersal? Journal of Ecology 98: 178-187.
Wilson, MD, Watts, BD, and DF Brinker. 2007. Status review of Chesapeake Bay marsh lands and breeding marsh birds. Waterbirds 30: 122-137.
Yamaura, Y, Taki, H, Makihara, H, Isono, M, Fujita, Y, and K Okabe. 2011. Revisitation of sites surveyed 19 years ago reveals impoverishment of longhorned beetles in natural and planted forests. Entomological Science 14: 56-67.
Over the last few posts, I’ve outlined the situation facing several owl species in decline- in general, although there are other factors with influence, the major culprits are habitat change and habitat loss. Since human populations often value the same areas used by owls, sometimes more for what they could be rather than for what they are, there is bound to be conflict between both groups. But there are also ways that we can contribute directly to owl conservation and make things a bit easier for our feathered friends.
