Is Avian Influenza Infecting Mammals Cause for Concern?

On February 9th, Colorado Parks and Wildlife (CPW) released information about various wildlife species testing positive for avian influenza. Among the critters found carrying the virus were a skunk, mountain lion, and black bear. All had died from the virus.

“All three of the confirmed cases showed signs of [avian influenza] before or after death including neurologic symptoms such as seizures or circling, general signs of illness such as weakness or lack of responsiveness to human presence, and organ damage including encephalitis, hepatitis, and pneumonia”, reported Travis Duncan with CPW.

The current strain of avian influenza is highly transmissible and was first detected in North America in wild geese in March 2022. In the past year, the virus has readily jumped from avian to mammalian species, which sounds alarming, but this phenomenon is not news.

Zoonotic diseases – diseases transmissible between humans and other animal species – are due to infectious agents that more than one species is susceptible to. Nearly every big game hunter is aware of disease transmission between livestock and elk – brucellosis and elk hoof disease are common examples. Transmissible spongiform encephalopathies cause diseases like scrapie in sheep, chronic wasting disease in deer and elk, mad cow disease, and Creutzfeldt-Jakob in humans. While these diseases are all different, the pathogenic vectors among species are typical and often include contact with bodily fluids or respiratory droplets.

The 2009 “swine flu” outbreak in the US was caused by the H1N1 influenza virus – the same virus that caused the “Spanish flu” in 1819. The swine flu virus appeared to be a new strain of H1N1 that resulted from a previous triple reassortment of bird, swine, and human flu viruses, which further combined with a Eurasian pig flu virus[1]. Miller et al. (2017)[2] identified 87 percent of swine pathogens listed by the World Organization for Animal Health cause clinical disease in livestock, poultry, wildlife, and humans.

Humans have contributed to zoonotic diseases through industrialization and the expansion of communities to accommodate the global population explosion[3]. Landscape development encroaches on wildlife and exposes species to pathogens through close contact with humans and livestock, etc.

Caserta et al. (2022)[4] tested white-tailed deer harvested by hunters for SARS-CoV-2 (COVID-19) during the 2020 and 2021 hunting seasons in New York State. Test results found only 0.6 percent virus occurrence in 2020, but 21.1 percent occurrence in 2021, including all three variants (Alpha, Gamma, and Delta). The variants were present in deer long after they had subsided in the local human population. This presents an example of wildlife acting as a “reservoir” for a virus that can infect other species. Still, it seems odd that a specific disease or pathogen can infect mammals, including humans, as well as birds.

Aquatic birds of the world are the reservoirs for all influenza A viruses, and the virus is spread by fecal-oral transmission in untreated water[5]. Transmission involves mutational or recombinational events and can occur through fecal contamination of unprocessed avian protein, e.g. animals preying upon infected birds or drinking contaminated water. The transmission of avian influenza viruses or virus genes to humans is postulated to occur through pigs that act as the intermediate host[5]. Once avian influenza viruses are established in mammals, they are transmitted from animal to animal by the respiratory airborne route.

While disease outbreaks and spread may be somewhat manageable among livestock and poultry populations, controlling disease spread in wildlife is complicated due to the free movement of wild animals. Brucellosis presents a textbook case study.

Cattle introduced brucellosis to the Yellowstone area in the early 1900s and transmitted it to local wildlife populations[6]. The disease has supposedly been eliminated from domestic livestock in the US, yet it remains in the bison and elk populations of the Greater Yellowstone Area[6]. Like many zoonotic diseases, brucellosis has not significantly threatened wildlife populations.

Understanding animal travel and contact networks is imperative to understanding a disease’s potential movement and risk – information that is not readily available for wild animals, particularly when facing a novel disease.

Researchers have studied ecological niche modeling as a means of predicting disease spread within and among wildlife populations, but data on levels of infection in wildlife are often scarce, open to bias, and insufficient for the assessment of cross-species transmission[7]. Complexities in wildlife populations including host movement, variation in host population size, density, and contact rates, unpredictable variation in climate, and species differences in the host–pathogen relationship lead to low model predictability.

Johnson et al. (2019)[8] found that adapting the traditional biotic, abiotic, and movement framework of ecological niche models by summarizing the interaction of three factors – dynamically linked biotic interactors, unlinked abiotic stressors, and dispersal capacity – improves model prediction capability. A practical application for common wildlife species seems unlikely; however, modeling disease spread with high predictability may allow wildlife managers to avoid significant population-level effects from novel and highly virulent pathogens for known distributions of threatened and endangered species.

The complexities involving host-pathogen interactions are utterly fascinating, but the discussion may be academic in the grand scheme of life and potential impacts on species at the population level. Animals and pathogens evolve continually together, each modifying their defense or attack strategy in a game of win, lose, or draw – the draw being the common outcome when an animal endures symptoms from the pathogen, recovers, and builds immunity.

Although unnerving, the cross-species spread of pathogens rarely leads to significant population-level effects. These interactions represent the pathology continuum that ebbs and flows through time. Take caution when handling game that appears to be sick and cook it thoroughly if it must be consumed.

You can read more about the effects of avian influenza on wild birds at Harvesting Nature.

Avian influenza – Unprecedented Spread Among Wild Birds – Harvesting Nature


[1] Trifonov V, H Khiabanian, and R Rabadan. 2009. Geographic dependence, surveillance, and origins of the 2009 influenza A (H1N1) virus. The New England Journal of Medicine 361 (2): 115–19.

[2] Miller, RS, SJ Sweeny, C Slootmaker, DA Grear, PA Di Salvo, D Kiser, and SA Shwiff. 2017. Cross-species transmission between wild pigs, livestock, poultry, wildlife, and humans: implications for disease risk management in North America. Scientific Reports 7:7821 | DOI:10.1038/s41598-017-07336-z.

[3] Fong, IW. 2017. Animals and mechanisms if disease transmission. In Emerging Zoonoses: Emerging Infectious Diseases of the 21st Century. Springer International Publishing DOI 10.1007/978-3-319-50890-0_2.

[4] Caserta, LC, M Martins, SL Butt, NA Hollingshead, LM Covaleda, S Ahmed, MRR Everts, KL Schuler, and DG Diel. 2022. White-tailed deer (Odocoileus virginianus) may serve as a wildlife reservoir for nearly extinct SARS-CoV-2 variants of concern. Proceedings of the National Academy of Science 120(6), https://doi.org/10.1073/pnas.2215067120.

[5] Webster, RG. 1997. Influenza virus: transmission between species and relevance to emergence of the next human pandemic In O Kaaden, C Czerny, and W Eichhorn, eds., Viral zoonoses and food of animal origin. Springer Vienna. https://doi.org/10.1007/978-3-7091-6534-8.

[6] Brucellosis – Yellowstone National Park (U.S. National Park Service) (nps.gov)

[7] Morgan, ER, M Lundervold, GF Medley, BS Shaikenov, PR Torgerson, EJ Milner-Gulland. 2006. Biological Conservation 131:244-254.

[8] Johnson, EE, LE Escobar, and C Zamrana-Torrelio. 2019. An ecological framework for modeling the geography of disease transmission. Trends in Ecology and Evolution 34(7):655-668. https://doi.org/10.1016/j.tree.2019.03.004.

*Feature Image Credit – USDA APHIS

Sage Grouse Translocation Reverses Population Decline

Published at Harvesting Nature, November 26th, 2021.

Think you’ve heard it all when it comes to greater sage grouse conservation? Think again. When an icon of the sagebrush ecosystem becomes imperiled, conservation dollars flow to the far corners of habitat and population research to find solutions to species sustainability and persistence.

Mary Meyerpeter and colleagues with the US Geological Survey and Idaho State University are currently studying translocation to stabilize or even grow two declining sage grouse populations on opposite fringes of their North American distribution. The “Bi-State” population on the California-Nevada border was selected as a small, isolated group facing low hatch success and overall decline. A North Dakota population was selected after a suffering a severe West Nile Virus outbreak, reduced the population.  

Wildlife translocation has been a tool in the scientific toolbox longer than the words “science” and “research” have been in existence, and with this tool comes many benefits to imperiled populations. Declining genetic diversity and abundance of reproductive individuals are two challenges recipient populations typically face that may be overcome by translocation. Precisely what Meyerpeter et al. had in mind, coupled with estimating the population-level effects of introducing new individuals to the imperiled populations, and removing individuals from the donor populations.    

From 2017 through 2019, the Bi-State population received 68 adults and 125 chicks from a nearby source population, while the North Dakota population received 137 adults and 66 chicks from an interior Wyoming population. The populations were monitored across the translocation period and continue to be monitored.

Photo by the US Fish and Wildlife Service

Preliminary study results suggest that translocation efforts have been successful for the recipient populations. The Bi-State population increased 160 percent with egg hatch success increasing from 31 percent to 86 percent. Similarly, the North Dakota population increased 188 percent compared to pre-translocation estimates.

The Bi-State donor population declined 31 percent following translocations, which may have been attributed to that population also being relatively small, among other potential factors. The Wyoming donor population showed no change.

Translocation results are considered preliminary until a monitoring period of up to five years has documented population responses, but the results appear promising. Additionally, successful translocation coupled with habitat restoration can perpetuate the species and play a role in range expansion into historic habitats.

Haying Best Management Practices for Wildlife

Farming and habitat practices to maintain healthy CRP and alfalfa stands provides significant nesting and brood rearing benefits to upland game birds, fawning areas for deer, and nesting and roosting habitat for wild turkey in the early spring and summer. Long, overhanging grasses provide nesting cover while broad-leaf plants like alfalfa and other native forbs provide insect forage for fledgling broods and hens. These stands draw and hold birds but have been called “ecological traps” in areas where haying regularly occurs.

The term ecological trap refers to a beneficial condition that attracts wildlife, but results in additive mortality, affecting the population overall. Quality CRP and alfalfa stands fit the scenario well where haying normally occurs during nesting season.

As haying equipment approaches, a hen pheasant may not vacate eggs or chicks, rather hunker down and use her camouflage for protection as a tractor passes by. This leaves birds vulnerable to the following mower which may be offset from the tractor. Likewise, small mammals and deer fawns use similar camouflage techniques and experience similar vulnerabilities to upland birds.

Best Management Practices

To minimize the potential hazardous effects of haying on wildlife, the Natural Resource Conservation Service has developed a few simple best management practices.

1) Defer haying. Apply and maintain at least two of the following management actions specifically for improving or protecting grassland functions for target wildlife species.

  • Do not cut hay on at least 1/3 of the hay acres each year. Idle strips or blocks must be at least 30 feet wide.
  • For at least 1/3 of the hay acreage, hay cutting must be either before and/or after the primary nesting or fawning seasons based on state established dates for the targeted species.
  • Increase forage heights after mowing to state specified minimum heights for the targeted species on all hayed acres.

2) For all haying during the nesting/fawning season implement at least two of the following to flush wildlife from hay fields during the mowing operation:

  • A flush bar attachment will be required on the mower (see figure below).
  • All mowing will be done during daylight hours.
  • Haying pattern:
    • Begin on one end of the field and work back and forth across the field, OR;
    • Begin in the center of the field and work outward.

Following these simple practices can greatly reduce unintentional wildlife mortality, further increasing the benefits of environmentally friendly farming.

flushing bar

Image from the Natural Resource Conservation Service.

 

Migratory Bird Treaty Act: 100 Years of Federal Protection

2018 marks the 100th year of the Migratory Bird Treaty Act (Act); one of the most influential laws in history that is critically important for protecting the variety of songbirds and raptors that we enjoy in North America. The Act prohibits take (killing), possession, import, export, transport, sale, purchase, barter, or offer for sale, purchase, or barter, any migratory bird, or the parts, nests, or eggs of such a bird except under the terms of a valid permit issued by the US Fish and Wildlife Service. What this means, is that no one can lawfully kill (intentionally or accidentally), or even reach down and collect a shed feather or take an abandoned nest from a non-game, migratory bird species.

Songbird species like cardinals, finches, juncos, and warblers typically come to mind as protected under the Act, but the Act actually protects about 1,000 species.

The Act came to be in response to the popularity of colorful bird feathers adorning hats and clothing dating back to the 1800s. The feather trade was tremendous and unregulated, and at the end of the century, several waterfowl species were hunted into extinction. Soon to follow were species like the passenger pigeon (photo below by James St. John), which was once the most abundant bird in North America, and possibly the world, with migratory flocks consisting of possibly billions of birds.

Ectopistes_migratorius_(passenger_pigeon) by James St John

The first legislation protecting migratory birds, the Lacey Act, was passed in 1900, and still stands today. The Lacey Act prohibits the sale of poached game across state boundaries. The Weeks-McLean Migratory Bird Act was passed in 1913 protecting migratory birds from being hunted during their spring migration; however, this act was soon ruled unconstitutional. In 1916, The United States entered into a treaty with Great Britain in which the two countries agreed to stop all hunting of insectivorous birds and to establish specific hunting seasons for game birds. Then in 1918, the Migratory Bird Treaty Act was passed as a means to implement the treaty with Great Britain.

The next major milestones following the creation of the Act came in 1970 when US courts began prosecuting oil, timber, mining, and utility companies for “take”. Though not directly targeting wildlife, these industries incidentally cause millions of bird deaths (“incidental take”) each year that could have been avoided with simple infrastructure modifications, according to the US Department of Justice (Audubon Society). Then, in 2001, President Clinton ordered all relevant federal agencies to consider migratory bird conservation as part of their regular decision making.

As one of the oldest federal wildlife regulations, the Act has saved millions, if not billions of birds, according the Audubon Society. One of the most obvious successes is the snowy egret (photo below by Frank Schulenburg), which was hunted to near extinction, but has rebounded splendidly. Over time, however, the Act has been tweaked here and there. In its final term, the Obama administration issued a legal opinion stating that the Act applied to the incidental killing of birds. Incidental take includes scenarios such as birds striking power lines or wind turbines and falling into open oil storage containers, but on a more literal note, a person unintentionally hitting a bird with a car. However, the Trump Administration has suspended that opinion, according to NPR.

snowy egret by Frank Schulenburg

So, what does this mean? It means that industry may no longer be held liable for the accidental death of a bird due to energy extraction such as timber harvest, or mountaintop removal mining. This also means it is no longer a crime to accidentally kill a bird while driving to work. While incidental take is nearly impossible to avoid or completely enforce, there are potential consequences to repealing industrial liability.

The Audubon Society cites the US Fish and Wildlife Services estimates of power lines killing up to 175 million birds a year, communications towers rack up to 50 million kills, and uncovered oil waste pits account for up to another 500,000 to 1 million. Data on wind turbines are harder to come by, but current estimates hover at about 300,000 bird fatalities a year. It is reasonable that the Trump Administration finds incidental take to be government overreach, but without potential repercussions for industry-related migratory bird deaths, entities may be less likely to implement costly best management practices that could reduce incidental take resulting from daily operations.

Collin O’Mara, president of the National Wildlife Federation, was cited saying the Obama Administration interpretation of the Act was too sweeping, while the Trump Administration interpretation is far too narrow. Although the future of the Act and its application is uncertain regarding incidental take, the Act has survived a passel of presidential administrations. Barring the abolishment of the Act entirely, the basis of the act, prohibiting intentional take, remains intact and is certain to provide continued protection for migratory birds.

For more information, keep an eye out on the US Fish and Wildlife Service and the Audubon Society websites.

US Fish and Wildlife Service

Audubon Society