Climate change speeds up bird molts- making them look older, faster

Molting patterns vary amongst different types of birds; some transition from their juvenile plumage to their adult feathers in one single molting cycle, while others may take years to reach their fully matured plumage.In the West Palearctic, encompassing Europe and parts of the Middle East and north Africa, songbirds typically lean towards the latter option, molting some of their feathers in one cycle and molting the rest at later points in time.3  As it is energetically costly to grow feathers, spreading molts out over longer periods of time can help offset energetic costs.  However, there is a reproductive tradeoff: the presence of juvenile feathers signal that the bird is young and not as competitively fit as an older bird with a whole set of adult feathers.  Interestingly, however, climate change may be changing up these molt patterns.3

The relationship between climate change and migration patterns has been well-studied; for short-distance migrants like many of the West Palearctic passerines, warming temperatures have led to them leaving for their wintering grounds later.2  Kiat et al. (2019) looked at the plumages of juvenile birds over 212 years and saw that their molting grew more extensive with climate change.  As they molt right after the breeding season, before migrating to their winter range, this change in migration timing may be giving birds more time to molt.3  They also saw that female birds have been molting more extensively than males in recent years, a reversal of past trends.3


Figure 1.  Diagram representing the increase in molt over time in two West Palearctic songbirds.  Adapted from Kiat et al. (2019)

     For birds, these changes in molting may affect their reproductive and social interactions.  A bird that molts its nest-grown feathers faster may look mature sooner than they did in past years.  On one hand, as Kiat et al. note, this may give younger birds an advantage in the reproductive scene, as quickly replacing their juvenile feathers allows them to compete with the older birds with regards to the attractiveness of their plumage.  On the other hand, looking more mature may also attract attention in the form of aggression from older birds, something that the juveniles may not be prepared to handle.3

The effects of this trend are in many ways still unstudied, and the effect of climate change may operate differently depending on a bird’s molt pattern and the climate conditions in which it lives.  For instance, birds like gulls and eagles may need as many as five years to reach their adult plumage, while smaller songbirds reach their mature plumage much sooner and may feel the effects of climate change more strongly.1  Either way, this phenomenon shows just how all-encompassing climate change can be, and how there are even more effects that researchers have yet to discover.

  1. All About Birds (2008) The Basics: Feather Molt. (last accessed 23 April 2022).
  2. Jenni L and Kéry M (2003) Timing of autumn bird migration under climate change: advances in long–distance migrants, delays in short–distance migrants.  R.  Soc.  Lond.  B.  270:1467–1471.  doi:10.1098/rspb.2003.23942.
  3. Kiat Y, Vortman Y and Sapir N (2019) Feather moult and bird appearance are correlated with global warming over the last 200 years.  Commun.  10, 2540(2019).  doi: 10.1038/s41467-019-10452-1.


New Zealand Tourism Consequences on Yellow-eyed Penguins

Yellow-eyed penguins at Katiki Point in New Zealand. Photo taken by Iain McGregor. Retrieved from


The yellow-eyed penguin is endemic to New Zealand and is also a popular cultural icon in New Zealand (Katz, 2017). However, over the years these penguins have faced population declines and are now considered to be endangered. Human disturbance has a large impact on the population of yellow-eyed penguins. A large cause of population declines comes from unregulated tourism (McClung et al., 2004). Since these penguins do not have many habituation opportunities, they are more sensitive to human tourism (French et al., 2018).

Tourism impacts stress, reproduction, and behavior in yellow-eyed penguins (Ellenberg et al., 2007). The presence of humans around these penguins causes an increase in stress-induced corticosterone. If this stress is prolonged or frequent, it can result in decreased fitness and survival in adults (Ellenberg et al., 2007). This increased stress can also impact the behavior of adults and their reproductive success (French et al., 2018).

Tourists often will ignore fences and signs in order to get closer to the penguins (Huffadine, 2018). Penguins in these touristed areas have lower breeding success and lower fledgling weights (McClung et al., 2004). A large reason for this is that the presence of tourism will cause the stressed penguins to change their behavior to avoid the humans. These changes in behavior include a decrease in the time spent at their nest, an increase in travel time, and an increase in the likelihood of nest abandonment (French et al., 2018). These changes in the behavior of adults cause negative impacts on the survival of their children.

Parental care is an important factor in the growth of fledglings. However, with the adult penguins spending more time avoiding the nests because of tourism, the fledglings receive lower provisions. Continuously missing meals or missing a meal during a year with poor food supply can lead to lighter fledgling weights and even death (Huffadine, 2018). Lower fledgling weight can have long-term population consequences like lower survival and recovery rates (McClung et al., 2004). It is important for humans to better mitigate the impacts of tourism in order to help protect this endangered species.


Ellenberg U., Setiawan A. N., Cree A., Houston D. M., Seddon P. J. (2007) Elevated hormonal stress response and reduced reproductive output in Yellow-eyed penguins exposed to unregulated tourism. General and Comparative Endocrinology, 152(1):54-63.

French R., Muller C., Chilvers B.,  Battley P. (2019). Behavioural consequences of human disturbance on subantarctic Yellow-eyed Penguins Megadyptes antipodes. Bird Conservation International, 29(2), 277-290.

McClung M. R., Seddon P. J., Massaro M., Setiawan A.N. (2004) Nature-based tourism impacts on yellow-eyed penguins Megadyptes antipodes: does unregulated visitor access affect fledging weight and juvenile survival?, Biological Conservation, 119(2):279-285.

Katz B. (2017) New Zealand’s Yellow-Eyed Penguins May Be in Trouble.

Huffadine L. (2018) People with selfie sticks are harming endangered yellow-eyed penguins.

The Mauritius kestrel is adjusting its phenology according to temperature changes

Photo credit: Willard Heck, retrieved from The Peregrine Fund,

As global temperatures warm, many species must make adjustments to their range or the timing of life-history events in order to continue to survive and reproduce in a changing world. Some species are considered more vulnerable to these changes, including species native only to islands because their limited range increases the risk to populations from climate events and they have a limited ability to disperse (Taylor et al. 2021). This greatly limits their capacity to adapt to climate change by relocating to a more suitable location with favorable conditions. As such, the only likely way to adapt to climate change for many island-endemic species is through phenotypic plasticity, by which animals alter the timing of life-history events such as reproduction (Taylor et al. 2021).

One such species is the Mauritius kestrel (Falco punctatus). This small bird of prey, native only to the small island of Mauritius in the Indian Ocean, was once the most endangered bird of prey in the world, with a population in the 1970s consisting of only two known breeding pairs, causing a genetic bottleneck where the existing gene pool was extremely limited (Jones et al. 1995). Thanks to repopulation efforts over several decades, the Mauritius kestrel made an incredible recovery and population estimates indicate there are now over 800 individuals (Jones et al. 1995). These birds of prey breed beginning in the dry spring, raising their young as the warm rainy season begins in the early summer (Taylor et al. 2021). But climate change could drastically alter seasonal patterns in Mauritius and put wild populations at risk of declining once more.

A new study published in 2021, however, shows that Mauritius kestrels may have a better chance of adapting to climate change than previously believed. Taylor et al. (2021) tracked rainfall patterns and breeding phenology of Mauritius kestrels between 1962 and 2016, along with other measures of breeding success. Between 1994 and 2014, the study found that the first egg-laying date advanced by about 0.7 days per year, influenced primarily by the mean temperature in the three-month period of July-September (Taylor et al. 2021). Additionally, Taylor et al. (2021) found that overlap of the rainy season with the breeding period had a negative impact on breeding success, favoring earlier breeding. Despite having experienced near-total extinction and an extremely limited gene pool, the population has retained phenological responses that are sufficient for it to track these environmental changes and adapt (Taylor et al. 2021). The Mauritius kestrel demonstrates phenotypic plasticity by adjusting its breeding period as temperatures increase, which may allow it to better adapt to changing environmental conditions despite being an island species that are considered to be more vulnerable to these same changes.


Taylor J, Nicoll MAC, Black E, Wainwright CM, Jones CG, Tatayah V, Vidale PL and Norris K. (2021). Phenological tracking of a seasonal climate window in a recovering tropical island bird species. Climatic Change 164:n.p.

Jones CG, Heck W, Lewis RE, Mungroo Y, Slade G and Cade T. (1995). The restoration of the Mauritius Kestrel Falco punctatus population. IBIS 137:173-180.

The Peregrine Fund. (n.d.). Mauritius Kestrel. Retrieved 5 March 2022 from

Climate Change Could Make it Harder for Hummingbirds to Conserve Energy Overnight

Many hummingbird species will soon be making their way back up to the United States to breed after a winter spent in Central America and Mexico, and their iridescent feathers and insect-like movement makes them hard to miss once they arrive.  But perhaps the most impressive thing about these tiny birds is their metabolism: some species show maximum heart rates of over 1,200 beats per minute, and their oxygen consumption outpaces even the best human athletes (Hargrove, 2005).  Having to feed every 15 minutes or so, life as a hummingbird certainly seems difficult, but the biggest struggle of such an active metabolism is sleeping for extended periods of time without their four meals per hour.

While they are not the only bird with this adaptation, hummingbirds actually have a strategy that allows them to sleep through the night without starving: overnight, hummingbirds enter torpor, a low-activity resting state that saves energy by allowing their body temperature and metabolic rate to fall far below their daytime measurements (Shankar et al., 2020).  More recently, studies have shown that hummingbirds are capable of entering both deep and shallow states of torpor, with deeper torpor leading to lower body temperatures and greater energy savings.  Shankar et al. (2022) looked at hummingbirds of different sizes and their body temperatures overnight.  The smallest species they studied, the Black-chinned Hummingbird, spent about half the night every night in a state of deep torpor that dropped their body temperatures from 30°C to 20°C.  Larger species like the Blue-throated Mountain-gems preferred to remain in shallow torpor for most of the night, only occasionally dipping into deeper torpidity.  The researchers hypothesized that entering deep torpor only when absolutely necessary gives the birds an advantage.  They may be more aware of predators, for example, and it takes less energy to bring their body temperature back up in the morning if the temperature doesn’t fall so low to begin with.  Because small animals have higher relative metabolisms, the tinier hummingbirds like the Black-chinned Hummingbird have less flexibility in choosing whether to use shallow or deep torpor.

(T) “Archilochus alexandri” by Mdf is licensed under CC BY-SA 3.0

(B) “Blue-throated Mountain-gem” by Alan Schmierer is licensed under CCO 1.0

     Torpor is a crucial ability for hummingbirds, allowing them to balance their constant need for food with the need to sleep.  Fortunately, studies show that climate change does not appear to affect a hummingbird’s ability to enter torpor (Shankar et al., 2020), but warming environments could still be a threat to its efficiency.  Warmer ambient temperatures could prevent hummingbirds from entering the deepest stages of torpor, meaning they would be using more energy just to get through the night.  This is a particularly important concern for the smallest hummingbirds with the highest metabolisms, as well as migratory hummingbirds that require the energy to fly thousands of miles every year.  To bring energy expenditures down, they can use a variety of strategies such as reducing their activity or eating more food, but that is often easier said than done.  Many hummingbird species have no choice but to migrate long distances, as their summer breeding grounds become cold and barren in winter.  And simply “eating more” can be a tall task for a bird that has to feed so often already (Hargrove, 2005).  Even a temperature change of a degree or two will affect the delicate biological processes these birds have developed to exist in their fast-paced worlds, but only time will tell if they can adapt to these new environments.



1. Hargrove JL (2005) Adipose energy stores, physical work, and the metabolic syndrome: lessons from hummingbirds. Nutr J 4(36). doi:10.1186/1475-2891-4-36.

2. Shankar A, Cisneros INH, Thompson S, Graham CH, Powers DR (2022) A heterothermic spectrum in hummingbirds. J Exp Biol 225(2):jeb243208. doi: 10.1242/jeb.243208.

3. Shankar A, Schroeder RJ, Wethington SM, Graham CH, Powers DR (2020) Hummingbird torpor in context: duration, more than temperature, is the key to nighttime energy savings. J Avian Biol 2020:e02305. doi:10.1111/jav.02305.

4. Spence AR and Tingley MW (2021) Body size and environment influence both intraspecific and interspecific variation in daily torpor use across hummingbirds. Funct Ecol 35(4):870-883. doi: 10.1111/1365-2435.13782.

5. Mdf. (2006, June 19). Archilochus alexandri / [Male Black-chinned Hummingbird (Archilochus alexandri) in flight, photographed in Moab, Utah, USA] [image/jpeg]. Wikimedia Commons.

6.  Alan Schmierer. (2013, April 26). Blue-throated Mountain-gem / [Male Blue-throated Mountain-gem (Lampornis clemenciae) in flight, photographed in Cochise Co., Arizona, USA] [image/jpg]. Flickr.



Microplastics Impact on Northern Fulmar Birds

I have attached screenshots of my Twitter thread looking at how Northern Fulmar birds are negatively impacted by microplastics in the ocean. This thread discusses how these birds commonly ingest these small plastics, and how it impacts the birds physiologically, such as endocrine disruption. There are so many ways to reduce our use of single-use plastic, and I’m hoping that this thread will bring about more awareness to this issue!

All photos are from the references listed below or CreativeCommons.


Costa M,  Ivar do Sul J (2013) The Present and Future of Microplastic Pollution in the Marine Environment. El Sevier, Environmental Pollution, 185: 352-364.

Galloway T, Lewis C (2016) Marine Microplastics Spell Big Problems for Future Generations. PNAS, 113 (9): 2331-2333

Herzke D et al. (2016) Negligible Impact of Ingested Microplastics on Tissue Concentrations of Persistent Organic Pollutants in Northern Fulmars off Coastal Norway. Environmental Science & Technology, 50 (4): 1924-1933.

Law KL, Thompson RC (2014) Microplastics in the Seas. Science, 345 (6193): 144-145.

Obbard R et al. (2014) Global Warming Releases Microplastic Legacy Frozen in Arctic Sea Ice. Earth’s Future, 2 (6): 315-320.

California: Banning Lead Ammunition to Save their Condors

The critically endangered California Condor (Gymnogyps californianus) is an avian scavenger and North America’s largest flying bird (West et al. 2017).  They have been experiencing population declines since the early 1950s and in 1980, the entire species consisted of only about 30 individuals.  Many doubted that these symbolic birds would do very well in captivity, but in 1987, all 27 of the remaining California Condors were captured and brought to a captive breeding facility. Teams of researchers from organizations such as the U.S. Fish and Wildlife Services, the Los Angeles Zoo, and the San Diego Wild Animal Park came together for these birds and by 1998, there were more than 150 California Condors (Meretsky et al. 2000). Today, there are now five breeding and release facilities in California and Mexico. There are now more than 400 California Condors, and half of these are flying free (National Park Service 2017).

So what was it that caused this species to drop to such small numbers in the first place? When scientists first started looking into this, they discovered that adults had higher mortality rates than immature condors (Meretsky et al. 2000). This was puzzling until they were able to study the tissues of dead condors and obtain blood samples from those that were captured for the captive breeding program. In the mid-1980s, lead poisoning was determined as the leading cause of death in wild California Condors (Wiemeyer et al. 1988).

Lead contamination is responsible for the deaths of millions of birds annually, and the main source of this is from hunting. California Condors are a scavenger species that feed on the carcasses of dead animals, and oftentimes they are feeding on carcasses that have been shot by hunters. Lead bullets, common ammunition used by hunters, shatter into tiny fragments upon impact. Because California Condors are known to scavenge communally, a single carcass containing these bullet fragments can poison several individuals (Kelly et al. 2014). Lead exposure was found to increase during hunting seasons. Sudden, severe symptoms of lead poisoning might include labored breathing, incoordination, and blindness. Chronic symptoms, which take longer to develop, might include changes in migratory movements or changes in bone mineralization, which increases the risk of bone fractures. The final stage of lead poisoning is death (Plaza and Lambertucci 2019).

Although eliminating lead from their environment is critical for the recovery of the California Condor, is it important to note that this is not the only contaminant that is threatening this species. Although California banned DDT in 1972, its influences are very present in this ecosystem today. DDE, a byproduct of DDT that does not get excreted from the body and actually becomes more concentrated over time, is consumed by the condors when they feed on marine mammal carcasses. Once ingested, DDE causes thinner eggshells, which increases the risk of the eggs breaking before the offspring have had a chance to develop (Kiff et al. 1979). Scientists have found that DDE disrupts the endocrine system of California Condors by changing the concentrations of reproductive hormones in their blood and the number of receptors that the hormones can send their signals to, which is what is ultimately causing the thinner eggshells. How lead is influencing the endocrine system in this species is not understood (Felton et al. 2015). Before we can fully address these contaminants that are reducing reproductive success through egg breakage, we need to focus our attention on reducing the amount of lead in the environment so we can increase the number of adults even attempting to nest.

The last two decades have seen the number of free-flying California Condors go from 0 to nearly 200 individuals. The real question is: are these birds still being affected by lead poisoning?

In 2008, California banned the use of lead ammunition for most hunting activities within the wild California Condor range. Annual blood samples found that the percent of these condors with more than 10 micrograms of lead per deciliter of blood was 67% prior to this ban (data from 1997-2008) and 62% after the ban (from 2008-2011) (Kelly et al. 2014). These results indicate that despite this ban, California Condors are still experiencing chronic exposure to lead poisoning. Because of this, California has decided to enact a state-wide ban on the use of lead ammunition for hunting, which is set to go into full effect on July 1, 2019. Perhaps this will be the key to the success of one of our country’s longest-running conservation programs. 




Felton RG, CC Steiner, BS Durrant, DH Keisler, MR Milnes, and CW Tubbs. 2015. Identification of California Condor estrogen receptors 1 and 2 and the activation by endocrine disrupting chemicals. Endocrinology 156(12): 4448-4457.

Kelly TR, J Grantham, D George, A Welch, J Brandt, LJ Brunett, KJ Sorenson, M Johnson, R Poppenga, D Moen, J Rasico, JW Rivers, C Battistone, and CK Johnson. 2014. Spatiotemporal patterns and risk factors for lead exposure in endangered California Condors during 15 years of reintroduction. Conservation Biology 28(6): 1721-1730.

Kiff LF, DB Peakall, and SR Wilbur. 1979. Recent changes in California Condor eggshells. Oxford University Press 81(2): 166-172.

Meretsky VT, NFR Snyder, SR Beissinger, DA Clendenen, and JW Wiley. 2000. Demography of the California Condor: Implications for Reestablishment. Conservation Biology 14(4): 957-967.

National Park Service. 2017. Condor Re-introduction & Recovery Program.

Plaza PI and SA Lambertucci. 2019. What do we know about lead contamination in wild vultures and condors? A review of decades of research. Science of the Total Environment 654 (1): 409-417.

West CJ, JD Wolfe, A Wiegardt, and T Williams-Claussen. 2017. Feasibility of California Condor recovery in northern California, USA: Contaminants in surrogate Turkey Vultures and Common Ravens. The Condor: Ornithology Applications 119(4): 720-731.

Wiemeyer SN, JM Scott, MP Anderson, PH Bloom, and CH Stafford. 1988. Environmental contaminants in California Condors. The Journal of Wildlife Management 52(2): 238-247.



All images were taken by former coworker, Louise Prévot, in Marble Canyon, AZ.

Climate Change Effects on an Out-of-Control Population: The Case of the Snow Goose

The Migratory Bird Treaty Act was enacted in 1918 as an effort to conserve migratory birds within North America and aimed to maintain or increase populations of various migratory birds, including waterfowl. These efforts have been successful in most species, but now waterfowl managers face a problem of overpopulation in snow geese (Ducks Unlimited, n.d.). These birds have grown substantially in population size as population estimates indicate numbers exceeding 15 million geese (Ducks Unlimited, n.d.). They have also expanded their breeding and nesting ranges throughout the Canadian Arctic and Sub-Arctic. The over-grazing of these areas has caused snow geese to find new habitat, and have destroyed vegetation that is crucial for foraging in snow geese (Peterson et. al, 2013). Other problems that are related to climate change include the decreased fitness in snow geese, reduced body size and condition of goslings, and new predation risks.

Snow geese have breeding grounds in the northern parts of Canada, but overpopulation and climate change are causing ranges to expand. Source: Environment Canada


Snow geese are the main driving force in the habitat degradation in the Hudson Bay area. They impact the vegetation and soil in a negative manner, which creates large patches of barren ground and makes it difficult for these habitats to recover even after the geese have moved out of the habitat (Peterson et. al, 2013). Also, climate change has caused these geese to inhabit new areas and degrade them as well (Peterson et. al, 2013). This causes problems for fitness and survival of geese, as lower resources decrease reproductive success and gosling survival. Aubry et. al. (2013) studied the effects of climate change, phenology, and habitat degradation on the body condition in snow goose goslings. Their findings show that goslings that live within the center of populations where habitat degradation was the worst had lower body condition and lower survival rates. Also, warmer winters and summers due to climate change result in lower body condition

This image shows an area that has been fenced off to keep snow geese out. The landscape around it has been destroyed by over-foraging of snow geese. Source: Wek’eezii Renewable Resources Board

scores for goslings, likely due to the reduced forage nutrition in plants (Aubry et. al, 2013). These factors could lower snow goose populations as they are reducing their nutrition and destroying their habitat.

Another change that has been observed is the difference in timing of migrations in snow goose populations. Climate change has caused a change in weather patterns and has altered the timing of snow goose migrations. These migrations appear to be happening earlier in the year, and geese are returning to their breeding grounds and nesting at earlier times (Bety et. al, 2004). It has been shown that geese that arrive earlier have better reproductive success than late-arriving geese. However, there are costs associated with arriving too early (Bety, 2004). These costs include harsh conditions in early spring that increase adult maintenance costs, less food availability, and increased predation (Bety et. al, 2004). It is shown that there is a benefit to arriving a few days earlier than average, but too early can decrease reproductive probability (Bety et. al, 2004). This indicates that birds that arrive at their breeding grounds much earlier than average have decreased fitness.

This table shows the changing in migration times and arrival and departure dates of snow geese. Source: Bety et. al, 2004

Climate change and the early arrival of snow geese to their breeding grounds have caused an increase of nest and adult predation and new predators are also a threat. Rockwell and Gormezano (2009) studied the effects of climate change on the arrival of polar bears on the nesting grounds of snow geese. The earlier melting of ice in the Hudson Bay has caused polar bears to come to shore earlier and reduced their predation on ringed seals. this has caused them to have a nutrient deficiency (Rockwell and Gormezano, 2009). This causes increased predation to snow goose nests, as the eggs provide the nutrients that the polar bears are lacking. These nests are easily preyed upon by polar bears and if this trend continues to increase, many snow goose colonies could suffer massive declines (Rockwell and Gormezano, 2009).

This graph shows the overlapping and advancing of snow goose nesting times and the arrival times of polar bears to nesting grounds. Source: Rockwell and Gormezano, 2009

These factors could eventually lead to a crash in snow goose populations as their resources could become depleted, their fitness levels drop, and they are at greater risk of predation. However, management actions are being implemented to decrease populations to sustainable levels. Changes in hunting regulations, as well as governmental intervention, are being used to control the overpopulation of snow geese. Historically, snow goose hunting seasons

Spring snow goose hunting seasons are one-way overpopulation is being managed. Source: Northern Skies Outfitters

have been during the fall migration and strict regulations were implemented to protect from overharvesting of populations. Now, spring seasons have opened in the United States and Canada to increase harvest numbers in snow geese (Lefebvre et. al, 2017). These seasons also reduce restrictions on hunting, such as allowing more than three rounds of ammunition to be loaded in a firearm at a time, allowing electronic calls and baiting, and an allowing more birds to be harvested ( Lefebvre et. al, 2017). The spring conservation harvests have had an impact on the reproductive ability of snow geese, as clutch sizes were smaller, laying date was later, and a decrease in reproductive activity. These effects were shown to be caused by the energy decreases and foraging decreases due to the disturbance caused by spring hunting (Lefebvre et. al, 2017).

Also, governmental agencies have enacted management plans to help control the populations and protect habitat. The U.S. Fish and Wildlife Service in conjunction with the Canadian Wildlife Service released a management plan in 2007 to control snow goose populations. Some of the efforts include nest and egg destruction, reproductive inhibitors, and mechanical, biological, and chemical control. The destruction of eggs and nests has little evidence of success in population controls, as geese will often lay additional eggs if the first clutch is destroyed (U.S. Fish and Wildlife Service, 2007). However, reproductive inhibitors such as conjugated linoleic acids have been observed to reduce eggs hatch rates (U.S. Fish and Wildlife Service, 2007). Mechanical control such as shooting and trapping have also been effective in reducing populations. Biological controls such as predators are effective at population control but may have unforeseen impacts on the rest of the habitat. Chemical controls such as poisons in bait are also being used to control snow goose populations but may cause mortality in unintended species (U.S. Fish and Wildlife Service, 2007).

The Canadian Wildlife Service has made management plans in conjunction with The U.S. Fish and Wildlife Service. Source: USGS

The U.S. Fish and Wildlife Service have made management plans in conjunction with the Canadian Wildlife Service. Source: U.S. Fish and Wildlife Service

The overabundance of snow goose populations is due to climate change and the ability of snow geese to thrive in many conditions, including warmer than average conditions. Snow geese continue to destroy their habitats and cause widespread destruction of the vegetation in the Hudson Bay region. Although management actions have been successful in slowing the growth of these populations, monitoring of these populations is crucial as snow geese can easily take advantage of changing environments and resources, and equilibrium numbers are challenging to maintain.






Aubry LM, Rockwell RF, Cooch EG, Brook RW, Mulder CPH, and Koons DN. (2013). Climate change, phenology, and habitat degradation: drivers of body condition and juvenile survival in lesser snow geese. Glob. Ch. Bio. 19:149-160.

Bety J, Giroux JF, and Gauthier G. (2004). Individual variation in timing of migration: causes and reproductive consequences in greater snow geese (Anser caerulescens atlanticus). Behav. Eco. And Sociobio. 57(1):1-8.

Humburg DD. (n.d.). Light goose dilemma: despite increased harvests, populations of these arctic-nesting geese continue to grow. Ducks Unlimited.

Lefebvre J, Gauthier G, Giroux JF, Reed A, Reed ET, and Belanger L. (2017). The greater snow goose Anser caerulescens atlanticus: managing an overabundant population. Ambio 46(2):262-274.

Peterson SL, Rockwell RF, Witte CR, and Koons DN. (2013). The legacy of destructive snow goose foraging on supratidal marsh habitat in the Hudson Bay lowlands. Arct. Antarct. and Alp. Res. 45(4):575-583.

Rockwell RF, and Gormezano LJ. (2009). The early bear gets the goose: climate change, polar bears, and lesser snow geese in western Hudson Bay. Pol. Bio. 32(4):539-547.

U.S. Fish and Wildlife Service. (2007). Alternatives. In: Final environmental impact statement: light goose management. U.S. Depart. of the Inter. pp 9-25.

Bioaccumulation & Biomagnification: A Heavy (Metals) Topic

In 1962 Rachel Carson published what is now recognized as one of the most important books in conservation literature, Silent Spring. Based on original research conducted in response to reports linking an observed decline in bird populations with widespread use of DDT as a pesticide in the 1950’s, the book broadly asserted that liberal use of DDT was contributing to considerable detrimental impact on the environment through trophic interactions. Although the book was met with considerable opposition from the chemical industry and lobbyists at the time, the academic community, along with the general public, defended the work. The book also emboldened the environmentalist movement, and eventually resulted in a ban on DDT in 1972, following president Nixon’s creation of the Environmental Protection Agency (EPA).

Bioaccumulation is a phenomenon that occurs when chemicals or toxins build in the tissues of organisms over time. One of the key problems with DDT is that at low concentrations it appeared to be harmless to vertebrate organisms, while being lethal to common pest invertebrates such as mosquitoes and flies. Thus, the negative effects of DDT on larger organisms such as mammals and birds were not initially apparent. DDT is not easily broken down through the metabolic pathway, yet readily passes across the gastrointestinal barrier. Organisms that consume organic material containing DDT will therefore accumulate the chemical in their fat stores, until eventually concentrations become lethal. However, such compounds can also be “passed up” the food chain in a process known as biomagnification. Insects such as mosquitoes that die from DDT exposure may find their way into water, where they are consumed by fish. Those fish then sequester the chemical in their tissues, and may then be consumed by larger predators such as eagles, osprey and falcons (Carson, 1962).

Although DDT has been banned for use in the U.S. except for in emergency situations, there are a number of other chemicals and compounds that have been known to bioaccumulate and biomagnify. Heavy metals such as mercury (Hg) are highly toxic to most living organisms. In particular, mercury causes permanent damage to a class of molecules called thioredoxin reductases (Carvalho, et. al., 2008), enzymes that are essential for proper cell growth and in counteracting oxidative damage from metabolic activity (Linster & Van Schaftingen, 2007). In an ecosystem-level study in Connecticut, it was shown that increases in mercury concentrations of fish were correlated with body size and age. Additionally, predators occupying the top of the food chain accumulated mercury the fastest, regardless of species identity (Neumann & Ward, 1999). Similar patterns of bioaccumulation and biomagnification have been observed in sharks in marine ecosystems (Maz-Corrau, et al., 2012), as well as montane stream ecosystems (Chasar, et al., 2009).

However, bioaccumulation of pollutants in aquatic ecosystems may have potentially devastating consequences for non-aquatic organisms as well. In particular, fish-eating sea birds are very susceptible to poisoning from industrial pollutants, as some compounds such as polychlorinated biphenyls (PCBs) are remarkably persistent in tissues (Walker, 1990). In a study conducted  at Kesterson Reservoir in California, bioaccumulation of selenium (Se) was observed in several species of birds, and correlated with reductions in adult body weight, and embryonic mortality (Ohlendorf, et al., 1990).

But bioaccumulation doesn’t just stop at birds and fish. Contamination of fisheries with metabolically stable compounds and chemicals has been reported across the globe, from Romania (Bravo, et. al., 2010) to China (Feng, et al., 2007). Even in the United States there is mounting concern that deposition of atmospheric heavy metals from industrial manufacturing and coal-fired power plants can reach fisheries via hydrologic processes such as runoff, and eventually affect human health (Driscoll, et al., 2007). After all, humankind has in many ways found its way to the top of the global food chain. So while the effects of bioaccumulation may seem a distant or alien concern in our isolated human ecosystem, it may not be long before heavy metals make their way onto our dinner plate.


Bravo, A. G., Loizeau, J. L., Bouchet, S., Richard, A., Rubin, J. F., Ungureanu, V. G., … & Dominik, J. (2010). Mercury human exposure through fish consumption in a reservoir contaminated by a chlor-alkali plant: Babeni reservoir (Romania). Environmental Science and Pollution Research, 17(8), 1422-1432.

Carson, R. (1962). Silent spring. Houghton Mifflin Harcourt.

Carvalho CM, Chew EH, Hashemy SI, Lu J, Holmgren A (2008). “Inhibition of the human thioredoxin system: A molecular mechanism of mercury toxicity.”. Journal of Biological Chemistry. 283 (18): 11913–11923.

Chasar, L. C., Scudder, B. C., Stewart, A. R., Bell, A. H., & Aiken, G. R. (2009). Mercury cycling in stream ecosystems. 3. Trophic dynamics and methylmercury bioaccumulation. Environmental science & technology, 43(8), 2733-2739.

Driscoll, C. T., Han, Y. J., Chen, C. Y., Evers, D. C., Lambert, K. F., Holsen, T. M., … & Munson, R. K. (2007). Mercury contamination in forest and freshwater ecosystems in the northeastern United States. BioScience, 57(1), 17-28.

Feng, X., Li, P., Qiu, G., Wang, S., Li, G., Shang, L., … & Fu, X. (2007). Human exposure to methylmercury through rice intake in mercury mining areas, guizhou province, china. Environmental science & technology, 42(1), 326-332.

Linster, C.L.; Van Schaftingen, E. (2007). “Vitamin C: Biosynthesis, recycling and degradation in mammals.”. FEBS Journal. 274 (1): 1–22.

Maz-Courrau, A., López-Vera, C., Galvan-Magaña, F., Escobar-Sánchez, O., Rosíles-Martínez, R., & Sanjuán-Muñoz, A. (2012). Bioaccumulation and biomagnification of total mercury in four exploited shark species in the Baja California Peninsula, Mexico. Bulletin of Environmental Contamination and Toxicology, 88(2), 129-134.

Neumann, R. M., & Ward, S. M. (1999). Bioaccumulation and biomagnification of mercury in two warmwater fish communities. Journal of Freshwater Ecology, 14(4), 487-497.

Ohlendorf, H. M., Hothem, R. L., Bunck, C. M., & Marois, K. C. (1990). Bioaccumulation of selenium in birds at Kesterson Reservoir, California. Archives of Environmental Contamination and Toxicology, 19(4), 495-507.

Walker, C. H. (1990). Persistent pollutants in fish-eating sea birds—bioaccumulation, metabolism and effects. Aquatic Toxicology, 17(4), 293-324.


Images (In Order of Appearance):

1st edition copy of Rachel  Carson’s Silent Spring. (

Illustration of the process of bioaccumulation and biomagnification. World Wildlife Fund. (

American Coot, one of the many species detrimentally impacted by bioaccumulation of selenium (

Coal fired power plant. Shutterstock. (