Tag Archives: Disease ecology

On Feeding Birds and Other Wildlife

2 Replies

There is a very large global movement to feed birds and I want to address why this is a human success story and could be an ecological disaster. These two alternatives follow from two divergent views of the role of humans in the world’s ecosystems. The first is the dominant view that humans are the most important species on Earth, and that we can design the world to maximize our wellbeing without concern of the ecological consequences. The second is a view that we are the custodians of the Earth and that our aim must be to conserve the Earth’s biodiversity and protect its ecosystems. The second view is gaining more visibility with the conservation movement, but if it is to become dominant, there are many ecological problems that deserve our attention. One of the most obvious ones is bird feeding. There are at present no global policies on feeding birds and views on feeding are controversial (Baverstock et al. 2019).

Humans feed birds because they like to look at them and because they have a general belief that feeding in winter or severe weather prevents bird deaths (Brock et al. 2021, Clark et al. 2019). If that is correct, we would expect to see that if we had one large area where birds were fed in winter, and another in which birds were not fed, there should be a difference in population size in the two areas in the following spring. I have yet to see any study that shows this differential effect. Consider an alternative hypothesis that feeding does indeed improve bird survival in winter, but this merely feeds more predators that now have a larger prey base, so the improvement is largely in the predator populations.  It is certainly true for some migratory bird species that if they are fed they can overwinter in more northerly areas or in cities and towns, so geographic winter ranges can expand.

Perhaps the most obvious impact of feeding birds and providing water is the transmission of diseases associated with feeding stations and bird baths. Lawson et al. (2017) explored this problem with bird feeding in Great Britain and found emerging diseases over a 25-year period, focusing on protozoan, viral, and bacterial diseases with contrasting modes of transmission. They also considered mycotoxin contamination of food residues in bird feeders, which present a direct risk to bird health. Rogers et al. (2018) described a mortality event in a declining population of band-tailed pigeons in California with a loss off about 18,000 pigeons associated with tricomonosis in a drought in which birds visited artificial water sites like bird baths. Purple et al. (2015) have demonstrated that the protozoan parasite Trichomonas gallinae could persist in bird baths.

There is a certain irony in the general belief that feeding improves the survival of wild birds. I am reminded of an old story about the English ornithologist David Lack who in the 1930s was talking to a local bird club about his long-term study for a life table of the English Robin. He reported from his banding studies that the life expectancy of the robin was about one year. After his talk, an elderly woman came up to him and started beating him over the head with her umbrella. Once she calmed down, she challenged him because she had a robin singing in her back yard for the last 10 years, so she assumed it was the same robin.

There are other consequences of feeding birds. One is the attraction of squirrels to bird feeders, and the subsequent displacement of birds. One study in southern England showed that grey squirrels occupied the feeders nearly half of the time they were in service (Hanmer et al. 2018). Another consequence of feeders is feed spilled to the ground which can attract rats and other less desirable species in urban settings. Many of these problems are not unique to bird feeding. Fležar et al. (2019) used cameras to investigate sites where European brown bears were being artificially fed year-round on plant-food and carrion from road kills in Slovenia. Over one year they detected 23 vertebrate species at the feeding sites in about 68,000 photos, most frequently brown bears, red foxes and European badgers, but also about half of the species coming to the feeding sites were birds. Roe deer also used these bear feeding sites, even though it is technically illegal to feed roe deer in this jurisdiction because deer feeding on corn and other plants materials can lead to fatal metabolic diseases. The key point is that feeding stations can attract a variety of non-target species with largely unknown consequences for the local wildlife community.  

It will take a brave set of ecologists and veterinarians to define and test the critical hypotheses that arise from feeding wildlife of any kind if only because of the vested interests of the bird seed producers along with so many humans who ‘know’ that feeding is ‘good’ for wildlife. The irony of all this in the end is that many people in parts of the Earth suffer from poor nutrition and starvation while in the first world we use agricultural products to feed birds and other wildlife.

Baverstock, S., Weston, M.A., and Miller, K.K. (2019). A global paucity of wild bird feeding policy. Science of The Total Environment 653, 105-111. doi: 10.1016/j.scitotenv.2018.10.338.

Brock, M., Doremus, J., and Li, Liqing (2021). Birds of a feather lockdown together: Mutual bird-human benefits during a global pandemic. Ecological Economics 189, 107174. doi: 10.1016/j.ecolecon.2021.107174.

Clark, D.N., Jones, D.N., and Reynolds, S.J. (2019). Exploring the motivations for garden bird feeding in south-east England. Ecology and Society 24, 26. doi: 10.5751/ES-10814-240126.

Fležar, Urša, Costa, B., and Krofel, M. (2019). Free food for everyone: artificial feeding of brown bears provides food for many non-target species. European Journal of Wildlife Research 65, 1. doi: 10.1007/s10344-018-1237-3.

Hanmer, H.J., Thomas, R.L., and Fellowes, M.D.E. (2018). Introduced Grey Squirrels subvert supplementary feeding of suburban wild birds. Landscape and Urban Planning 177, 10-18. doi: 10.1016/j.landurbplan.2018.04.004.

Lawson, B., Robinson, R. A., and Cunningham, A. A. (2018). Health hazards to wild birds and risk factors associated with anthropogenic food provisioning. Philosophical Transactions of the Royal Society, Biological Sciences 373 (1745): 20170091. doi: 10.1098/rstb.2017.0091.

Purple, K.E. and Gerhold, R.W. (2015). Persistence of two isolates of Trichomonas gallinae in simulated bird baths with and without organic material. Avian Diseases 59, 472-474. doi: 10.1637/11089-041115-Reg.1.

Rogers, K.H., Girard, Y.A., Woods, L.W., and Johnson, C.K. (2018). Avian trichomonosis mortality events in band-tailed pigeons (Patagioenas fasciata) in California during winter 2014–2015. International Journal for Parasitology: Parasites and Wildlife 7, 261-267. doi: 10.1016/j.ijppaw.2018.06.006.

Why Science is Frustrating

Leave a reply

Many people train in science because they are convinced that this is an important route to doing good in the world. We operate on the simple model that science leads to knowledge of how to solve problems and once we have that knowledge the application to policy and management should be reasonably simple. This model is of course wildly incomplete, so if you are a young person contemplating what to do with your life, you should perhaps think very carefully about how to achieve progress. I review here three current examples of failures of science in the timely management of acute problems.

The first and most complex current problem is the Covid-19 pandemic. Since this virus disease became a pandemic more than a year ago, many scientists have investigated how to thwart it. There was spectacular success in developing vaccines and advances in a basic understanding the virus. However, some proposals had no value, and this was often because the scientific papers involved were not yet peer reviewed but were released to the news media as though they were the truth. All the common mistakes of scientific investigation were in clear view, from simple hypotheses with no testing to a failure to consider multiple working hypotheses, to a failure to evaluate data because of non-disclosure agreements. Speed seemed to be of the essence, and if there is a sure way to accumulate poor science it is by means of speed, including little attention to experimental design, probabilities, and statistical analysis. Many books will soon appear about this pandemic, and blame for failures will be spread in all directions. Perhaps the best advice for the average person was the early advice suitable for all pandemics – avoid crowds, wash your hands, do not travel. But humans are impatient, and we await life going “back to normal”, which is to say back to rising CO2 and ignoring the poor.  

A second example is the logging of old growth forests. Ecologists all over the world from the tropics to the temperate zone have for the last 40-50 years decried logging practices that are not sustainable. Foresters have too often defended the normal practices as being sustainable with clever statements that they plant one tree for every one they cut, and look out your car window, trees are everywhere. It is now evident to anyone who opens their eyes that there is little old growth left (< 1% in British Columbia). But why does that matter when the trees are valuable and will grow back in a century or two or four? Money and jobs trump biodiversity and promises of governments adopting an “old-growth logging policy” appear regularly, to be achieved in a year or two. The tragedy is written large in the economics where for example in British Columbia the local government has spent $10 billion in the last 10 years supporting the forestry industry while the industry has contributed $6 billion in profits, not exactly a good rate of return on investment, particularly when the countryside has been laid waste in the process. Another case in which economics and government policy has trumped ecological research in the past but the need to protect old growth forests is gaining with public support now.

A third example comes again from medicine, a fertile area where money and influence too often outrace medical science. We have now a drug that is posed to alleviate or reduce the effects of Alzheimer’s, a tragic disease which affects many older people (Elmaleh et al. 2019, Nardini et al. 2021). A variety of drugs have been developed in an attempt to stop the mental deterioration of Alzheimer’s but none so far has been shown to work. A new drug (Aducanumab) is now available in the USA for treatment of Alzheimer’s but it already has a checkered history. This drug seemed to fail its first major trials yet was then approved by the Federal Drug Administration in the USA over the protests of several doctors (Knopman, Jones, and Greicius 2021). Given a cost of thousands of dollars a month for administering this new drug to a single patient, we can see the same scenario developing that we described for the forest industry and old growth logging – public pressure for new drugs resulting in questionable regulatory decisions.

There are several general messages that come out of this simple list. The most important one is that science-on-demand is not feasible for most serious problems. Plan Ahead ought to be the slogan written on every baseball hat, sombrero, Stetson, toque and turban to remind us that science takes time, as well as wisdom and money. If you think we are having problems in the current pandemic, start planning for the next one. If you think that drought is now a problem in western North America, start hedging your bets for the next drought. Sciences moves more slowly than iPhone models and requires long-term investments.

I think the bottom line of all the conflict between science and policy is discouraging for young people and scientists who are doing their best to unravel problems in modern societies and to join these solutions to public policy (González-Márquez and Toledo 2020). Examples are too numerous to list. Necessary policies for controlling climate change interfere with people’s desires for increased global travel but we now realize controls are necessary. Desirable human development goals can conflict with biodiversity conservation, but we must manage this conflict (Clémençon 2021). The example of feral horses and their effects on biodiversity in Australia and the USA is another good example of a clash of scientific goals with social preferences for horses (Boyce et al. 2021). Nevertheless, there are many cases in which public policy and conservation have joint goals (Tessnow-von Wysocki and Vadrot 2020, Holden et al. 2021). The key is to carry the scientific data and our frustration into policy discussions with social scientists and politicians. We may be losing ground in some areas but the present crises in human health and climate change present opportunities to design another kind of world than we have had for the last century.

Boyce, P. N., Hennig, J. D., Brook, R. K., and McLoughlin, P. D. (2021). Causes and consequences of lags in basic and applied research into feral wildlife ecology: the case for feral horses. Basic and Applied Ecology 53, 154-163. doi: 10.1016/j.baae.2021.03.011.

Clémençon, R. (2021). Is sustainable development bad for global biodiversity conservation? Global Sustainability 4. doi: 10.1017/sus.2021.14 2021.14.

Elmaleh, D.R., Farlow, M.R., Conti, P.S., Tompkins, R.G., Kundakovic, L., and Tanzi, R.E. (2019). Developing effective Alzheimer’s Disease therapies: Clinical experience and future directions. Journal of Alzheimer’s Disease 71, 715-732. doi: 10.3233/JAD-190507.

González-Márquez, I. and Toledo, V.M. (2020). Sustainability Science: A paradigm in crisis? Sustainability 12, 2802. doi: 10.3390/su12072802.

Holden, E., Linnerud, K., and Rygg, B.J. (2021). A review of dominant sustainable energy narratives. Renewable & Sustainable Energy Reviews 144. doi: 10.1016/j.rser.2021.110955.

Knopman, D.S., Jones, D.T., and Greicius, M.D. (2021). Failure to demonstrate efficacy of aducanumab: An analysis of the EMERGE and ENGAGE trials as reported by Biogen, December 2019. Alzheimer’s & Dementia 17, 696-701. doi:/10.1002/alz.12213.

Nardini, E., Hogan, R., Flamier, A., and Bernier, G. (2021). Alzheimer’s disease: a tale of two diseases? Neural Regeneration Research 16, 1958. doi: 10.4103/1673-5374.308070

Tessnow-von Wysocki, I. and Vadrot, A.B.M. (2020). The voice of science on marine biodiversity negotiations: A systematic literature review. Frontiers in Marine Science 7, 614282. doi: 10.3389/fmars.2020.614282.

On Disease Ecology

Leave a reply

One of the sleepers in population dynamics has always been the role of disease in population limitation and population fluctuations. Part of the reason for this is that disease studies need cooperation between skilled ecologists and skilled microbiologists. Another problem is the possibility of infinite regress in looking for disease agents as a cause of population change in natural populations – e.g. if it is not virus X, there are hundreds of other viruses that might be the culprit. In both North America and Europe one focus of concern has been on the hantavirus group (Luis et al. 2010; Mills et al. 2010, Davis et al. 2005, Mills et al. 1999). Hantaviruses come in many different forms and are typically carried by rodent species. Some varieties produce hemorrhagic fever with renal syndrome in Europe, Asia and Africa, but in the Americas the main disease of concern is HPS (hantavirus pulmonary syndrome). It is no surprise that often emerging diseases are studied only because some humans die from them. As of 2016, 690 cases of hantavirus pulmonary syndrome have been recorded in the USA, and 36% of these cases resulted in death. The reverse question of what the disease is doing to the animal population gets rather less attention typically than the human disease problem. The example I want to discuss here is the Sin Nombre virus (SNV) in deer mice (Peromyscus spp.), widespread rodents in North America.

The hantavirus outbreak in the Southwestern USA in the 1990s caused numerous human deaths and produced a number of field studies that showed a patchy pattern of infection among deer mice in Arizona and Colorado (Mills et al. 1999). Male mice were infected more than females and the suggestion was that males fighting for territories were infecting one another directly when population densities were high. The call for long-term studies went out and several studies from 3-5 years were carried out in the late 1990s until the problem of infection in the human population became less of an issue compared with other diseases such as Ebola in other parts of the world. The shift in concern resulted in reduced funding for field studies in North America.

In 1994 Rick Douglass and his research team began long term studies on the Sin Nombre virus in deer mice using 18 live trapping areas of 1 ha each spread across Montana and placed in a variety of habitats (Douglass et al. 2001). Long-term for their study was 15 years, all this at a time when 2-3 year studies were thought to be sufficient to unravel the nexus of infection and transmission. The idea was to complement in Montana similar rodent research in Arizona, New Mexico, and Colorado. The results are fascinating and important because they illustrate the importance of long term research and the understanding of what a well designed field study can produce.

Rightfully many of the hantavirus studies were focused on the human connection, but what I want to emphasize here is the impact of this virus on the rodent populations. Luis et al. (2012) estimated that male Peromyscus had their monthly survival rate reduced from 0.67 to 0.58 if they were seropositive, a 13% reduction, but females showed no effect of hantavirus on survival so that infected and uninfected females survived equally well. Hantavirus does reduce body growth rates of infected male mice. One consequence of these findings should be that the growth rate of Peromyscus populations in Montana should be only slightly affected by hantavirus infections, since it is the female component of the population that drives numbers. There are limitations to these conclusions since juveniles too young to live trap could suffer mortality that at present cannot be measured. The threshold for hantavirus transmission in these Peromyscus populations was about 17 individuals per ha (Luis et al. 2015), implying that hantavirus would disappear in populations smaller than this because it would not transmit. The consequence for us is that human hantavirus infections in North America are much more likely when deer mouse populations are high, and by monitoring deer mice ecologists can broadcast warnings when there are increased possibilities of infection with this lethal disease.

The details about the Sin Nombre hantavirus in North America are well covered in these and other papers. The most important general message from this research has been the need for long term studies to get at what might initially seem to be a simple population problem (Carver et al. 2015). There are a host of other viruses that infect rodent species and many other mammals and birds about which we know very little. The path to understanding the effects of these viruses on the animals they infect and their potential for human transmission will require much detailed work over a longer time period than what is now the funding horizon of our granting agencies. The Montana studies on the Sin Nombre virus required ecologists to trap for 20 years with more than 851,000 trap nights to catch 16,608 deer mice, and collect 10,572 blood samples to assess infections and gain an understanding of this virus disease. The problem too often is that it is easy to find ecologists and virologists keen to cooperate in these studies of disease, but it is not easy to find the long term funding that looks at these ecological problems in the time scale of 10-20 years or more. We need much more long term thinking about ecological problems and the funding to support team efforts on difficult problems that are not soluble in a 3-year time frame.

Carver, S., Mills, J.N., Parmenter, C.A., Parmenter, R.R., Richardson, K.S., Harris, R.L., Douglass, R.J., Kuenzi, A.J., and Luis, A.D. 2015. Toward a mechanistic understanding of environmentally forced zoonotic disease emergence: Sin Nombre hantavirus. BioScience 65(7): 651-666. doi: 10.1093/biosci/biv047.

Davis, S., Calvet, E., and Leirs, H. 2005. Fluctuating rodent populations and risk to humans from rodent-borne zoonoses. Vector-Borne and Zoonotic Diseases 5(4): 305-314.

Douglass, R.J., Wilson, T., Semmens, W.J., Zanto, S.N., Bond, C.W., Van Horn, R.C., and Mills, J.N. 2001. Longitudinal studies of Sin Nombre virus in deer mouse-dominated ecosystems of Montana. American Journal of Tropical Medicine and Hygiene 65(1): 33-41.

Luis, A.D., Douglass, R.J., Hudson, P.J., Mills, J.N., and Bjørnstad, O.N. 2012. Sin Nombre hantavirus decreases survival of male deer mice. Oecologia 169(2): 431-439. doi: 10.1007/s00442-011-2219-2.

Luis, A.D., Douglass, R.J., Mills, J.N., and Bjørnstad, O.N. 2010. The effect of seasonality, density and climate on the population dynamics of Montana deer mice, important reservoir hosts for Sin Nombre hantavirus. Journal of Animal Ecology 79(2): 462-470. doi: 10.1111/j.1365-2656.2009.01646.x.

Luis, A.D., Douglass, R.J., Mills, J.N., and Bjørnstad, O.N. 2015. Environmental fluctuations lead to predictability in Sin Nombre hantavirus outbreaks. Ecology 96(6): 1691-1701. doi: 10.1890/14-1910.1.

Mills, J.N., Amman, B.R., and Glass, G.E. 2010. Ecology of hantaviruses and their hosts in North America. Vector-Borne and Zoonotic Diseases 10(6): 563-574. doi: 10.1089/vbz.2009.0018.

Mills, J.N., Ksiazek, T.G., Peters, C.J., and Childs, J.E. 1999. Long-term studies of hantavirus reservoir populations in the southwestern United States: a synthesis. Emerging Infectious Diseases 5(1): 135-142.