Author: Jessica Gallardo
If you catch yourself in the Sierra during the early summer months at alpine elevations, you’ll likely see these little passerine birds with brown bodies, pink flecks among their plumage and gray-crowned heads; these birds are known as the gray-crowned rosy-finch (Leucosticte tephrocotis). You are likely to see them flying around the glacial lakes that decorate the Sierra, feeding on the mayflies that hover around... or you might find that they are no longer frequenting the lakes due to the introduction of invasive trout (2). Alternatively, you can turn to the snowcaps that linger on alpine elevations to find gray-crowned rosy-finches (GCRF) picking at the insects trapped in the blankets of snow... or you might find that they no longer hang around due to the absence of snow (1). Whether it is the introduction of invasive species outcompeting them or climate change impacting their food source, these small alpine birds are being affected through anthropogenic effects that ultimately impact their environment and affect their physiology (3). Although not much is yet known about the GCRF, there is still growing concern regarding its survival and what can be done to help these alpine birds.
The Impacts of Invasive Trout on the GCRF
During the summer months, recreational fishing becomes popular in the Sierra and there are a lot of people that visit the lakes in the Sierra specifically to fish. While fishing itself is a great way to get outside, the explosion of popularity in the sport has led to some complications for native wildlife. Since the 1800’s, non-native fish like the trout have been introduced into these fishless lakes that were left behind when glaciers receded (4). This compromises the pristine habitats that organisms inhibit or that rely on them like the GCRF. The GCRF’s breeding season occurs during the early months of the summer and aligns with the emergence of the forementioned mayfly. While the GCRF raise their young, they heavily rely on aquatic insects like the mayfly. The reason for this is that it makes-up about 38% of the GCRF’s diet for their young and without that significant contribution of nutrition, the GCRF would be losing out on a significant part of their meal source (2). Of course, with the introduction of invasive trout into the glacial lakes, these GCRF face competition for one of their biggest food sources in the Sierra. Peter Epanchin found that mayflies were typically absent in glacial lakes containing trout and an abundance of mayflies in lakes that were fishless. Epanchin also found that the GCRF avoided lakes that had trout in them due to the lack of food abundance in them; it was a deterrent for them to compete against other GCRF for limited food. Instead, the GCRF were more likely to encroach on one another in fishless lakes where the mayflies were abundant. With limited food availability and increasing competition, the future populations of the GCRF remain uncertain.
Climate Change and the Continuation of the Altering of the GCRF’s Environment
While humans have altered the amount of food available to the GCRF, we also continue to alter their environment with climate change (1) and ultimately, their physiology and reproduction abilities. The GCRF occupy these specialized areas, called niches, that are fragile and constantly changing under the threat of climate change, making the GCRF more susceptible to any changes in their environments. With human evolution increasing at an unsustainable speed, the rise in temperatures and ongoing droughts, the alpine environments are altering at a rate that raises the question again, what will happen to the GCRF? There lies concern with the receding snowcap because the GCRF forage for insects that get stuck in the snow as their main source of food (1). The lack of snowfall and continuing droughts also mean that the GCRF will continue to alter their fundamental niche which continues to recede along with the snowcap. These receding snowcaps, ongoing droughts, and shifting baselines on what the GCRF’s fundamental niche is means further uncertainty of implications for this alpine bird and its increasing crisis regarding food unavailability.
How Physiology is Altered Due to Changes in the Environment and Lack of Food Resources
With the environment of the GCRF changing as well as its food sources, it was found by H. Bobby Fodkins that available energy or food quantity/quality can influence physiological processes like reproduction, growth, development, and the immune system. It was also recognized that there can be disruptions in the cues for timing reproductive activities (3). This evidence indicates that with the ongoing food insecurity in the lakes and with the lack of snow to trap insects, the GCRF could face physiological changes from these anthropogenic, or human-made, effects. Fodkins also found that while birds have a short-term adaptive response to food unavailability/unpredictability, it can be destructive over time. This is due to increased stress levels that use up stored fat and protein energy reserves in birds, supporting the chronic stress hypothesis which suggests that variation in access to food can induce a prolonged stress response, resulting in maladaptive usage of energy reserves and increased behavioral activity. In other words, just how human’s physiology and well-being can be altered by stressful events or situations, birds have a similar response with how stress impacts their own well-being. With the introduction of invasive trout into glacial lakes that help provide nutrient subsidies for the GCRF and lack of snowcaps to entrap insects, this stressful environment could negatively impact their reproduction and population. Already, there has been a significant decline in the numbers of the GCRF compared to those of historical numbers and it may continue in a negative trend if something is not done to improve the various threats that these birds face (2).
Hope in the Fight for Survival
While humans have negatively impacted the environment and food sources for these little alpine birds, we have also strived to correct them. Today there is more awareness now than ever before in history about the dangers of climate change not only to the GCRF but to the entire planet. Countries are uniting in the fight against climate change with agreements like the Paris Agreement which is the framework within the United Nations on climate change, mitigation, adaption, and finances. There are also existing entities like the U.S. Department of Agriculture that help oversee invasive species preventions, practices, and regulations. Though not much is known about these alpine birds, there is hope for the survival of the GCRF with ongoing awareness, practices, and education.
Key Terms: Gray-Crowned Rosy-Finch, Climate Change, Invasive Species, Bird Physiology,
1. Brown, E., Lozano, R., Yoo J., and Brown C. 2020. Impact of Annual Snowpack on the Abundance of the Sierra Nevada Gray-Crowned Rosy Finch. CAMINO. https://camino.ucsc.edu/wp-content/uploads/2020_cohort_Zavaleta.pdf
2. Epanchin, P.N., Knapp, R.A., and Lawler, S.P. 2010. Nonnative trout impact on alpine-nesting bird by altering aquatic-insect subsidies. Ecological Society of America 91(8). https://doi.org/10.1890/09-1974.1
3. Fokidis, H.B., Roziers, M.B., Sparr, R., Rogowski, C., Sweazea, K., and Deviche, P. 2012. Unpredictable food availability induces metabolic and hormonal changes independent of food intake in a sedentary songbird Journal of Experimental Biology. 215(16). https://doi.org/10.1242/jeb.071043
4. Knapp, R.A. Non-Native Trout in Natural Lakes of the Sierra Nevada: An Analysis of Their Distribution and Impacts on Native Aquatic Biota. 1996. Sierra Nevada Ecosystem Project: Final report to Congress. Vol. 3. http://www.highsierrahikers.org/issue_fish_main.html
5. Siegel, R. B., P. Pyle, J. H. Thorne, A. J. Holguin, C. A. Howell, S. Stock, and M. W. Tingley. 2014. Vulnerability of birds to climate change in California's Sierra Nevada. Avian Conservation and Ecology 9(1): 7. http://dx.doi.org/10.5751/ACE-00658-090107
"Gray-crowned Rosy-Finch" by Tom Benson is licensed with CC BY-NC-ND 2.0.
"Gray-crowned Rosy-Finch (Hepburn's)" by Tom Benson is licensed with CC BY-NC-ND 2.0.
Author: Megan Penland
Keywords: Climate Change, Hummingbirds, Distributions
This beautiful little hummingbird is known as the Sparkling violet ear humming bird (Colibri coruscans). C. coruscans is covered in iridescent green feathers, with patches of blue on its neck, stomach, and under its eye; and patches of blue violet feathers on its ears which is where it’s name comes from. C. coruscans are about 13-14 cm in length, including the tail, which is 6 cm long. Males typically weight a bit more that the females; ranging from 7.7 to 8.5 grams, and 6.7 to 7.5 grams, respectively. (1) C. coruscans is commonly seen in the highland areas of south America, including the Andes mountains, occurring in a wide range of semi open habitat, including parks and city gardens (2). C. coruscans ‘s range starts from the north of Bolivia, going up all along the west coast of South America—through Bolivia, the Andes, Peru, Ecuador, Colombia—until stopping at the coast of Venezuela. C.corusans lower elevation limit is 1700 meters, and it’s current higher elevation limit is 4,500 meters. (2) C. coruscans also is a typically high elevation hummingbird that migrates to lower elevations to molt (3). C. coruscans is territorial. It is known that the average generation length—the average age of all parents—of C. corusans is 4.2 years. (2) little is known about the mating system of C. coruscans, but what is confirmed is that females do the majority of the nest building and brooding, typically laying two eggs. (1) However, it has been seen on occasion that males come back to help incubate and care for their young, (5) which is uncommon for most hummingbird species. C.coruscans, like most hummingbirds, are primarily nectarivores—organisms that consume nectar. C. coruscans typically drink from small, clustered flowers and have a preference for long, red, tubular flowers; such as Firebush (Hamelia patens) and Firespike (Odontonema strictum). They will also eat small insects that they catch in flight. (4) C. coruscans has been predicted to shift its territory range upwards in elevation due to climate change, which could impact how it flies, the range of its food, and how it sleeps.
Elevation and Wingbeats
Rising temperatures due to climate change have been predicted to cause a shift upwards in many neotropical hummingbird ranges. In a study projecting climate change temperatures, scientists found that for 29 different neotropical hummingbird taxa the changing heat climate will cause an average change in elevation of around 300-700m to stay within ancestrally preferred temperatures—for the C. coruscans specifically, the average change in elevation expected to occur was the most extreme, with a 3158-meter difference.(3)The study was initially concerned about this ascent and hypothesized that the change in elevation would lead to a change in the way hummingbirds fly; predicting that the hummingbirds would need to flap more broadly or more frequently due the lower amount of oxygen available at higher elevations. This turned out to not be as big of a concern as was first thought, though; after the study had concluded that, despite a predicted impressive ascent of 3158 meters, the range of a wing stroke for C. coruscans only widened by a statistically insignificant 16 degrees. The change in elevation was predicted to cause other issues.
Impacts of climate change on hummingbird food distribution
The more pressing issue for neotropical hummingbirds like C. coruscans posited by the researchers of the previous study was the independent migration of plant species that C. coruscans currently feeds on and the reassembling of these vegetation types could lead to random and unknown species associations for pollination of these plants and the survival of hummingbirds they end up paired with. One paper looked at the distributions of Andean trees and found that they moved upslope at an average of 2.5-3.5 vertical meters per year. The migration rates for individual genuses varied wildly (6). It’s not much of a stretch to imagine hummingbirds being impacted as plant ranges change due to global warming—as certain nectar producing plants die out or shift ranges due to changing climate, that along with C. coruscans shifting range to stay within it’s ancestrally preferred climates, will cause intense strain to be put on the newly formed individual mutualisms of C. coruscans and the plants left in its range it can feed on. This strain will be even more pronounced when taking interspecific competition with other nectarivores into account, as C. coruscans is territorial, and will need to expend even more energy to defend the plants they have access to. As explored by Fiensinger et. al, the cost of a hummingbirds hovering is one of the most energetically expensive forms of flight—this added with the cost of shifting mutualisms and defending territory, leads to an energy output high enough that it will expend more energy foraging than it will obtain from the nectar foraged, and/or the cost of simply hovering will be so high it will not be able to energetically afford to chase intruders off of it’s territory. This along with the cost of hovering slowly increasing as elevation increases, may cause species to become so inefficient at high altitudes, that the species will drop out of the ecosystem entirely (7).
Shifting temperatures and Hummingbird torpor
On top of all the possible interspecies conflict caused with the migration of plants, the shifting temperatures may cause issues with the Sparkling violet ear’s sleep pattern. Hummingbirds like the sparkling violet ear usually go into a state of torpor during the night—torpor being a state similar to hibernation, with a slowed pulse and metabolic rate; but happening routinely, in this case, on a daily basis—in order to conserve energy during the cold nights. One study investigated torpor in Andean hummingbirds at approximately 3800 meters above sea level by monitoring body temperature and the mass lost overnight. C. coruscans was found to be in a torpor state for 6.18 hours a night on average, losing approximately 6.79% of it’s body weight in the process. Before this state of torpor, it was observed loading up on nectar in preparation. (8) A shift upwards in elevation could cause more intensely cold nights, causing torpor to be more costly, thus losing more fat reserves and having it be much more difficult to sufficiently load up on nectar energy enough before dark as they do now.
Climate change is a very broad threat, which can make it difficult to look closely at highly specific subjects or issues. How the C. coruscans (or the Andean ecosystem as a whole) will respond to specific aspects of climate change is not something that is closely studied. Specifically, There was little information on how oxygen availability shifts with increased elevation in the context of C.coruscans’s (or any other high elevation hummingbird) high need for oxygen exchange. The predicted shifts in C. coruscans’s preferred Andean flora specifically in response to climate change is unknown. What little we know of these shift may suggest conservation actions such as, figuring out which plants, if any, are energetically suitable food sources for C. coruscans and will be most likely to spread upwards into the C. coruscans’snew projected territory. If such a plant exists, it could saved in a seed bank or propagated so it could ensure future possible food sources for C. coruscans. Study could also be put into how the energetic cost of the projected change in elevation could influence things like mating and reproduction.
- Hummingbirds: Trochilidae - Sparkling Violet-Ear (Colibri Coruscans): Species Accounts. Sparkling Violet-Ear (Colibri Coruscans): Species Accounts - Ears, Birds, Male, and Feathers - JRank Articles, Jrank, animals.jrank.org/pages/861/Hummingbirds-Trochilidae-SPARKLING-VIOLET-EAR-Colibri-coruscans-SPECIES-ACCOUNTS.html.
- BirdLife International. 2016. Colibri coruscans. The IUCN Red List of Threatened Species 2016: e.T22687114A93140619. https://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T22687114A93140619.en. Downloaded on 26 April 2021.
- Buermann, W., Chaves, J. A., Dudley, R., McGUIRE, J. A., Smith, T. B., & Altshuler, D. L. (2011). Projected changes in elevational distribution and flight performance of montane Neotropical hummingbirds in response to climate change. Global Change Biology, 17(4), 1671-1680.
- Stoppelmoor, G. (2000) Captive Breeding of the Sparkling Violet-ear Hummingbird. AFA Watchbird, 27(1), 52-54.
- Hainsworth, F. R. (1977). Foraging efficiency and parental care in Colibri coruscans. The Condor, 79(1), 69-75.
- Feeley, K. J., Silman, M. R., Bush, M. B., Farfan, W., Cabrera, K. G., Malhi, Y., ... & Saatchi, S. (2011). Upslope migration of Andean trees. Journal of Biogeography, 38(4), 783-791.
- Feinsinger, P., Colwell, R., Terborgh, J., & Chaplin, S. (1979). Elevation and the Morphology, Flight Energetics, and Foraging Ecology of Tropical Hummingbirds. The American Naturalist,113(4), 481-497. Retrieved April 25, 2021, from http://www.jstor.org/stable/2460270
- Wolf, B. O., McKechnie, A. E., Schmitt, C. J., Czenze, Z. J., Johnson, A. B., & Witt, C. C. (2020). Extreme and variable torpor among high-elevation Andean hummingbird species. Biology Letters, 16(9), 20200428.
Image 1: A Sparkling Violet-ear Hummingbird."Sparkling Violet Ear Hummingbird-7190" by Don Burkett is licensed under CC BY-NC-SA 2.0, https://www.flickr.com/photos/dtburkett/19852824129
Image 2: Illustration of changing plant distribution and Sparkling Violet-ear territory by Megan Penland under CC permissions.
Author: Camille Kuta
The California condor is one of the largest birds in North America with a wingspan of around 9 feet and males weighing up to 26 pounds, with females being slightly smaller. It is covered in black feathers, except for its bald reddish-pink or yellow head and white triangular underwing patches. Like a chameleon, the condor’s head can even change color, depending on its mood (1)! The rare bird is a meat-eating scavenger that prefers large mammal carcasses such as deer and sheep and beached marine mammal carcasses like whales and sea lions. Condors begin their day in the late morning, soaring high above ground in slow circles alone or in small groups. They spend much of their time perched on high cliff sides (1). The California condor has one of the longest life spans of birds worldwide; they can live up to 60 years. Condors mate for life and the female lays an egg every other year. While the condor’s range used to stretch the American Southwest and the West Coast, now it is found only in some parts of California, Utah, and Arizona. The species is critically endangered, and in 1987 there were no condors living in the wild because all remaining 22 condors were captured and put into breeding programs. They were reintroduced to the wild in 1991, and now the fragile population is at about 500 individuals.
What Threats Do Condors Face?
Eating Like a Bird
California condors face many threats to their species, and receive intensive population management currently. One of the prevalent threats the condors face is lead poisoning from consuming lead ammunition found in animal carcasses (2). Free-flying condors have seen no change in their chronic lead exposure, even after regulations and bans on some lead ammunition, meaning it is unclear how effective these regulations are (2). The condor’s diet changing over time could be a hypothetical solution to the lead poisoning threat. The condor’s diet changed from having a large proportion of marine mammals to being mostly terrestrial mammals (3). The shift from a partially marine to a mostly terrestrial diet seems to match up with the reduction of whale, seal and sea lion populations due to commercial whaling and hunting from the 1700’s to the early 1900’s for their blubber, meat, bones, and fur (3). Currently, many of these populations are growing due to environmental protections. The large populations of marine mammals across the coasts of California may provide a valuable niche for a self-sustaining California condor population.
Birds of a Feather Flock Together
Another difficulty that condor populations face is their decreased genetic diversity after there were so few condors left to repopulate the species in 1987. This phenomenon is called the bottleneck effect, and the lack of genetic diversity can cause harmful mutations to become common in a group, similar to the haemophilia found in the incestuous European royalty. Species that go through a bottleneck effect, as the California condors did, are in danger of having increased chances of rare recessive alleles. One study found a rare trait that has become more prevalent in California condor populations is having 14 tail feathers instead of the usual 12 (4). Though this oddity does not affect the condor’s life in a negative way, it shows how dangerous recessive traits, such as chondrodystrophy, a lethal form of dwarfism, could become more common in condors due to their small population size (5). Chick afflicted with chondrodystrophy have severely shortened legs, twisting of the long axis, and death, as well as less common symptoms such as shortening of the mandibular beak. California condors were found to suffer from chondrodystrophy at an unusually high rate (5). Though this is a sad and fatal condition, it is debatable how much people should interfere with condors’ natural breeding behavior to reduce harmful recessive genes in the population.
A Bird in the Hand...
It is possible that the extreme human intervention the condors recieve can affect them negatively. Human’s intensive management and handling of condors can raise stress hormone levels in condors. Chronic stress and highly stressful events can negatively affect an animal’s physiological health, just like it can for humans. Due to condor populations being so fragile, all wild individuals have markers and are captured biannually to monitor their health and blood-lead levels. It was found that condors had generally increased stress hormones following handling events (6). Hopefully, if condor populations grow and stabilize, they will receive less constant human intervention and stress.
What can we do?
Though the California condor populations have recovered from the extreme bottleneck event in 1987, the species still faces many dangers and requires human intervention to monitor population health. Despite the close contact with researchers, there is much more to study when it comes to this rare and beautiful bird. Individuals can help by learning more about the movements to save the condor. One campaign, Get the Lead Out, focuses on stopping toxic lead from entering the food chain and poisoning wildlife. Joining and supporting movements like Get The Lead Out show how important wildlife and biodiversity is to the general public. The more people supporting protection of biodiversity, the more change can be made.
All images illustrated by Camille Kuta.
- Clark, William S., et al. “Raptors of Mexico and Central America.” Princeton University Press, (2017): 97-98. Project MUSE. muse.jhu.edu/book/48935.
- Finkelstein, Myra E., et al. “Lead Poisoning and the deceptive recovery of the critically endangered California Condor.” Proceedings of the National Academy of Sciences 109.28 (2012): 11449-11454.
- Chamberlain, C. P., et al. “Pleistocene to recent dietary shifts in California condors.” Proceedings of the National Academy of Sciences 102.46 (2005): 16707-16711.
- Pryor, D.L. and Ralls, K. “Fourteen tail feathers: An autosomal recessive trait in california condors (Gymnogyps californianus).” Zoo Biology, 36 (2017): 1-4.
- Ralls, K. et al. “Genetic management of chondrodystrophy in California condors.” Animal Conservation (2000): 3, 145–153.
- Glucs, Zeka E., et al. “Glucocorticoid measurement in plasma, urates, and feathers from California condors (Gymnogyps californianus) in response to a human-induced stressor.” PLoS ONE 13 (2018): e0205565.
Author: Jane Weichert
The effect of anthropogenic activity on gentoo penguins
Growing up we all heard the slogan “save the polar bears,” as it was an amazing way to spark children's curiosity in climate change; these large mysterious creatures whose homes were falling apart because of anthropogenic, or human, activities. Well, polar bears are not the only warm and fuzzy animals who are feeling the effects of climate change. Pygoscelis papua, also known as gentoo penguins, live on the Antarctic Peninsula and its surrounding islands and while their population is actually growing, they are experiencing the damaging effects of tourism everyday .
How is the gentoo population both growing and shrinking?
As temperatures continue to rise in the Antarctic Peninsula, areas that were historically covered in ice are beginning to show the land beneath them. While this disruption hurts many populations that rely on the icey-cover to survive, gentoo penguins actually prefer ice-free areas including coastal plains, sheltered valleys, and cliffs . Thus, as more habitat becomes available for the gentoo penguins their populations expand--who doesn’t love a new hangout spot!
However, not all is well. Many of the original colonies of gentoo penguins are heavily affected by tourism, having a negative impact on their daily lives. Gentoo penguins form life-long bonds with their partners and work together to build their nests and raise their chicks (more information on gentoo penguin couples and other background information can be found here). Penguin couples can become distracted or irritated by large crowds and loud sounds, the effects of which can be seen in their mating and breeding successes. In a highly visited population on Goudier Island, Port Lockroy, there has been a 1.4% decrease in breeding pairs and 3.8% decrease in chicks raised per year . The overall decrease in mating and breeding success in highly visited colonies leads to a significant decrease in the number of individuals in these populations. These trends are seen in many of the largely visited populations around the Antarctic Peninsula.
A growing population is not always a good thing.
The overall population of gentoo penguins has grown by 11% since 2013 . Continuing to expand across the Antarctic Peninsula, the two edge colonies, meaning the individuals that live furthest apart, have less and less contact with each other. Because of this distance they are unable to breed regularly, decreasing the population's gene flow. Gene flow is the ability of an individual, or its genetic material, to migrate from one population to another. If there is too little gene flow between populations, the populations can actually morph into two separate populations.
There is evidence of the two edge populations becoming genetically separate. While they may look alike, there are key genetic differences between the populations. To read more about the separation of populations click here . As the population becomes more and more separate, threats of infertile chicks increases, because their mother and father may no longer be genetically compatible. This new pattern could lead to a decrease in population size, because chicks will still be laid, however the parents will not know if it is fertile or not until it has grown.
There is still a lot of hope for the gentoo penguins!
The Committee for Environmental Protection and the International Association of Antarctica Tour Operators have set regulations on the amount of tourism in Antarctica in order to protect the wildlife from increased stress levels . Many researchers have focused on comparing anthropogenically induced stress levels of gentoo penguin populations to the typical amount of stress experienced by non-visited populations. The research shows there are no major effects of stress on the physiology, or normal body functions, of gentoo penguins .
While there has been some research done about microplastics found in gentoo penguin diets, little is known about how this affects their physiology . Researchers should focus on how these microplastics are entering their bodies, through their food sources or through direct ingestion, and how these microplastics affect them.
Other research should focus on the possible effects of genetic mutations on the physiology of gentoo penguins. As the edge populations become genetically separate, how will the colonies evolve to better suit the habitat they are expanding into.
- M. J. Dunn et al., A long-term study of gentoo penguin (Pygoscelis papua) population trends at a major Antarctic tourist site, Goudier Island, Port Lockroy. Biodiversity and Conservation. 28, 37–53 (2018), doi:10.1007/s10531-018-1635-6.
- Gentoo Penguin. Wild Republic (available at https://www.wildrepublic.com/product/gentoo-penguin/).
- Gentoo Penguin: National Geographic. Animals (available at https://www.nationalgeographic.com/animals/birds/facts/gentoo-penguin).
- Contrary to the fears of some, penguins and people do mix. The Economist (available at https://www.economist.com/science-and-technology/2019/07/11/contrary-to-the-fears-of-some-penguins-and-people-do-mix).
- R. Herman et al., Update on the global abundance and distribution of breeding Gentoo Penguins (Pygoscelis papua). Polar Biology. 43, 1947–1956 (2020), doi:10.1007/s00300-020-02759-3.
- L. R. Pertierra et al., Cryptic speciation in gentoo penguins is driven by geographic isolation and regional marine conditions: Unforeseen vulnerabilities to global change. Diversity and Distributions. 26, 958–975 (2020), doi:10.1111/ddi.13072.
- M. A. Lynch, et al., Tourism and stress hormone measures in Gentoo Penguins on the Antarctic Peninsula. Polar Biology. 42, 1299–1306 (2019), doi:10.1007/s00300-019-02518-z.
- F. Bessa et al., Microplastics in gentoo penguins from the Antarctic region. Scientific Reports. 9 (2019), doi:10.1038/s41598-019-50621-2.
"Gentoo Penguins" by D-Stanley is licensed under CC BY 2.0 To view the terms, visit https://search.creativecommons.org/photos/abbdc733-b33d-4993-9016-3bb2e5b8d343
"Gentoo Penguin with chick" by Liam Quinn is licensed under CC BY-SA 2.0 To view the terms, visit https://search.creativecommons.org/photos/672cefa2-1bc8-426d-a5e0-aa101e08f19d
Authors: Nick Bergeron, Caroline Brandt, Cristela Ramirez
Urbanization is the way of the future, but sadly it comes at a cost. Urbanization refers to the sprawl of civilization created by developing the land into cities and other human-made areas. Biodiversity around the world is being lost as urbanization fractures and destroys habitats. The red-tailed hawk, with its extensive range throughout North America, is no stranger to the threat of urbanization (1). Red-tailed hawks have mostly thrived despite urbanization due to their ability to adjust to almost any habitat. While they are currently able to adapt, this may not be the case as human populations rise and urbanization continues to convert and fragment natural habitats. Luckily, a host of research and conservation efforts dedicated to red-tailed hawks exists to protect them.
Within the urban sprawl, green spaces are the areas that retain some natural habitat. A few examples of green spaces are parks, golf courses, empty fields, and large backyards. The question is: why are green spaces important? Despite habitat loss and fragmentation, red-tailed hawks are thriving in urban areas. Their home ranges are even smaller in these urban areas compared to rural areas, suggesting that urban areas are acting as a higher quality habitat (2). That might seem counterintuitive, but green spaces play an important role in this. They provide food resources, refugia, and pockets of natural habitat. The size of red-tailed hawk home ranges is directly related to the amount of green space within their home range. Interestingly, their home ranges are smaller when the green spaces are more fragmented, this is likely because larger green spaces are heavily developed, while smaller patches are left more natural as they are not as profitable to develop (2). The components that dictate the home ranges of red-tailed hawks are complex and green spaces are only one part, more research needs to be done to fully understand them. Although red-tailed hawks are thriving in urban environments, their success does not come without issue.
In the Sky: A light at the end of the tunnel!
Red-tailed hawks often fall victim to aircraft collisions. In fact, they are one of the ten most frequently hit birds by aircraft in the United States (3). Collisions may be dangerous and even fatal at times for humans and hawks alike. Not to mention, aircraft groundings due to these collisions result in economic losses in millions of dollars every year (3). Aircraft currently lack means for repelling red-tailed hawks and other birds.
Research within the last 50 years explores lights as deterrents for birds. New research points to short wavelength LED lights as the key to deterring birds in flight from aircraft and other areas that may endanger them. Birds can see into the violet and ultraviolet portions of the UV spectrum, some of the shortest wavelengths of the light spectrum, much better than the human eye (3). Results of experiments with short-wavelength LED’s look promising; the red-tailed hawks showed clear avoidance from them (3). The effectiveness of LED’s is good news for humans and birds.
Compared to lasers, a previous candidate for avian-avoidance strategies, LED lights are very low-hazard for human eyes. By using these lights on planes and runways, we may reduce collisions, keeping hawks and humans safe. The LED’s may also function well on mobile units to deter hawks from colliding with tall buildings, cell phone towers, and large-scale power generation plants (3). Biohazardous areas like oil spills and reservoirs for toxic waste may use LEDs to keep hawks from living there too (3). The technology of LED’s is continually evolving, becoming a more reliable and cost-effective tool, especially in the future of protecting red-tailed hawks.
Navigating the Industrial Dangers of Urbanization
It looks as if red-tailed hawks are not ready to leave the city, and measures can be taken to protect them from hazards presented by continuing urbanization and industrial development. As local human populations increase, so does the demand for conveniences such as electricity. Yet, live electrical wires pose a threat to birds and without protection, more raptor deaths than anticipated may continue to be seen (4). Local governments tend to impose safety risks by continuing to allow exposed wires to hang low. The risk of electrocution can be reduced by installing high sitting pylons - or posts where the wires are organized and attached for distribution. High sitting, protected pylons have reduced the amount of demised feathered friends of any stature - raptors or otherwise- by the hundreds (4).
Other sites of energy collection are coalbeds, where methane extraction takes place. As more land is allocated for these sites of extraction, natural habitats continue to be fragmented. The difference between these spaces being used for housing or business development as opposed to energy development is that red-tailed hawks do not want to nest near these disturbed coalbeds (5). A study that focused on a coalbed methane extraction site revealed that nesting raptors became displaced from the area as development continued. The nesting period is a critical time for the raptor, and industrial energy development near its nesting site affects its ability to be fertile (5). Without the protection of these natural habitats and nesting sites, red-tailed hawk populations may be negatively affected.
Red-tailed hawks’ futures look hopeful, as long as we consider their needs as urbanization continues. Smart city planning, with lots of natural green spaces, and protection from hazards, can help supply habitat and food sources for urban hawks. We can significantly reduce their fatalities from aircraft collisions with the help of short-wavelength LED lights by putting them on aircraft and airfields, and these lights may be used to keep the birds out of harm’s way in other unsafe urban areas. Being sensible about the energy we use and having a citywide plan to safely seek those resources is another important step in protecting these hawks. Urbanized areas will never compare to nature’s ability to provide for red-tailed hawks, so we must continue to conserve what natural habitat is left within and outside of our cities. Feeling inspired to get involved after reading this? There are some simple things that anyone can do to help red-tailed hawks and other wildlife. A great way is to advocate for the creation and preservation of natural habitat within your local communities. Another is to elect officials who understand the importance and value of conservation. With a little effort, urbanization does not have to be a death sentence for wildlife and biodiversity!
Photograph of a red-tailed hawk soaring with the moon in the background-Credit: By Mike Baird from Morro Bay, USA - Red-tailed Hawk with moon over Estero Bay CA - composition red-tail-moon-composite-2630s, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=32354021
Photograph of downtown Chicago-Credit: Public Domain, https://commons.wikimedia.org/w/index.php?curid=143884
- Preston, C. R. and R. D. Beane (2009). Red-tailed Hawk (Buteo jamaicensis), version 2.0. The Birds of North America (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.52
- Morrison, J. L., Gottlieb, I. G. W. & Pias, K. E. Spatial distribution and the value of green spaces. Urban Ecosystems 19, 1373-1388 (2016).
- Foss, C. R., Ronning, D. J., & Merker, D. A. (2017). Intense short-wavelength light triggers avoidance response by Red-tailed Hawks: A new tool for raptor diversion? The Condor, 119(3), 431–438. https://doi.org/10.1650/CONDOR-16-230.1
- Demeter, I., Horváth, M., Nagy, K., Görögh, Z., Tóth, P., Bagyura, J., … Harness, R. E. (2018). Documenting and reducing avian electrocutions in Hungary: a conservation contribution from citizen scientists. The Wilson Journal of Ornithology, 130(3), 600. doi: 10.1676/17-031.1
- Carlisle, J. D., Sanders, L. E., Chalfoun, A. D., & Gerow, K. G. (2018). Raptor nest–site use in relation to the proximity of coalbed–methane development. Animal Biodiversity and Conservation, 41(2), 227–243. doi: 10.32800/abc.2018.41.022
Authors: Adrienne Cotton, Allyson DiLorenzo, Lynda Cameron
Imagine this: you’re walking the streets of your local city, maybe to your favorite coffee shop or bakery, when all of a sudden you hear a piercing shriek from above. You look up just in time to see a flash of grey, black and white dive down from a light post and swoop right in front of you. You run from the attack, only looking back to find out what in the world that was once you no longer hear the screeching calls. Imagine your surprise when you see that despite the ferocity of the barrage, your attacker is a relatively small, seemingly inconspicuous bird; the Northern Mockingbird, Mimus polyglottos, to be specific. This is increasingly becoming a story that many city-living people can attest to, but despite the bombardment seeming like a personal act of aggression, it truly isn’t. You were just in the wrong place at the wrong time, standing too close to the most important thing in the world to these birds -- their nest full of helpless chicks.
Besides being known for dive-bombing unlucky pedestrians, Northern Mockingbirds are often recognized for their characteristically cocked tail, distinctive white wing markings, and incessant calling that often mimics other bird species. The males are slightly larger than the females but not by much, and they typically choose one mate for the entire breeding season but some may partake in other mating styles despite the parenting being nearly equally shared (1). Northern Mockingbirds have been found to live 8-10 years in the wild but much longer in captivity. They are not picky eaters and will eat a wide variety of arthropods, fruits, earthworms and sometimes small lizards, which some researchers believe is one aspect that has helped the species move into a wide variety of habitats including cities (1). Found on every American continent, these birds have adjusted so well to urban life that they are often called “urban exploiters” and have left many scientists wondering how these persistent little loud-mouths are able to thrive amongst humans while so many others cannot (2). This mystery has led to many scientific studies that delve into the complex consequences urban life has on the birds’ success. Despite the stresses of urban noise, light, and human disturbances, these songbirds have acclimated many stages of their reproduction process to help them more effectively find mates, protect their nest, and feed their chicks.
Finding Each Other Through the Noise
Urban background noise, or the excess noise made by cars, machines, and other loud aspects of city life can cover, or mask, certain frequencies made by songbirds. In the springtime, male mockingbirds rely on the audibility of their songs in order to find mates. Like human women swoon over the smooth voice of John Legend or any other male artist, lady mockingbirds are attracted to a man who can sing. The question is, does the frequency masking unintentionally created by our urban background noise cause male mockingbirds to have a less effective mating song? Studies have discovered that mockingbirds avoid having their voices masked by refraining from the use of easily masked frequencies (3). They also selectively sing unmasked frequencies more often, thereby increasing mating call success and overall fitness. Whether they do this by mimicking other successful songbird species in the area or by learning to use unmasked frequencies themselves is unknown; however, the exploitation of unmasked frequencies is unique to urban populations of mockingbirds, showing this is one way that living in close proximity of humans changes the mating behavior of the species.
Threat or Not, the Mockingbird Knows Who You Are
Once a male successfully woos a lady mockingbird with his serenade, it’s time to start nesting. The birds choose a spot up in a tree or on a light-post to build their cup-shaped nest out of sticks, dry grass and leaves. The female lays anywhere from two to six eggs over the span of a few days and keeps them warm by sitting on them for about twelve to thirteen days until the chicks begin to hatch. During this time and until the chicks leave the nest around twelve days after hatching, the parents are on high alert for any threat that may come to their helpless babies (1). This especially applies to mockingbirds nesting in urban areas surrounded by so much human commotion. Much like how a parent is more attentive to their child’s safety when in a crowd, these birds have to have a keen awareness of threats when caring for their chicks in cities. But aggressive defense responses are energetically costly, so assailing every pedestrian walking past just isn’t practical for birds in populated areas. For Northern Mockingbirds, the solution to this problem has been a cognitive one: they can recognize human individuals and base their response on whether or not that person has previously shown themselves to be a threat to the nest (2). Since most people don’t pose an actual threat to mockingbird nests, this recognition helps birds in the most populated areas habituate to human presence while still actively defending when necessary. Some scientists also suggest this may help them identify actual urban danger such as cats and predatory birds. And while there are many unanswered questions about how this all works and came to be over generations, it is obvious that Northern Mockingbirds benefit from being able to recognize individuals and decide whether or not aggression is needed.
Feeding Hungry Mouths into the Night
Along with protecting the nest from predators, nesting mockingbirds must also provide large quantities of food for the helpless hatchlings. In urban environments with excessive amounts of light being emitted twenty-four hours a day, these diurnal birds are encouraged to hunt their prey (primarily large insects like moths, which are drawn to lights themselves) and perform other daytime behaviors late into the bright night (4). The artificial light provided by street lamps, billboards, cars and buildings has provided an environment in areas like parking structures where the Northern Mockingbirds hunt and feed nestlings at times they normally wouldn’t in nature (5). Like a college student waking up for breakfast at one in the afternoon, the bird’s feeding behaviors are seemingly disheveled. While their ability to change their behavior may be helpful for feeding hungry nestlings in a volatile environment, it may negatively impact them over time as they continue to go against their natural tendencies. Still, exploiting their artificially lit environment in this way shows yet another way the Northern Mockingbird makes due in a human dominated world.
Is the Northern Mockingbird Really Here to Stay?
The Northern Mockingbird obviously has changed in numerous ways in order to exploit urban obstacles and successfully reproduce in the concrete jungle we have built. Whether or not humans and mockingbirds can continue to coexist is up to us, especially as we continue to significantly change the environments that they live in which may overtime prove to be too stressful for even these urban-adapted birds. Hopefully as technology gets more advanced and electric cars become the majority, the noise made by gas powered vehicles may be greatly reduced and allow mockingbirds to return to more normal song frequencies (although they seem to be keeping up pretty well so far). By increasing public knowledge and respect of nesting birds, we can curtail the stress of defending nests from harmless humans and hopefully allow for better nest outcomes. Another huge help to urban mockingbird populations would be a decrease in light pollution in active nesting areas so that birds can follow a more natural circadian cycle. And while these changes may seem nearly impossible now, there is absolutely hope: researchers are constantly working to find new technology and methods of protecting a variety of species through better city planning and public education. So next time you or someone you know gets dive-bombed on the street by a little grey bird, remember: they're not being mean, they’re doing the best they can to make it as a city-slicker just like you.
Photo Credit Acknowledgements
Adrienne Cotton Photography (article author, 2018)
Berntsen, Nicolai. 2015. “Times Square never shined so bright.” Image downloaded from https://unsplash.com/photos/F3uyey6ours
1. K. C. Derrickson, R. Breitwisch, Northern Mockingbird (Mimus polyglottos). The Birds of North America. 007, (1992).
2. D. J. Levey, G. A. Londoño, J. Ungvari-Martin, M. R. Hiersoux, J. E. Jankowski, J. R. Poulsen, C. M. Stracey, S. K. Robinson, Urban mockingbirds quickly learn to identify individual humans. Proceedings of the National Academy of Sciences Of the United States of America. 106:22, 8959-8962 (2009).
3. M. J. Walters, R. P. Guralnick, N. J. Kleist, S. K. Robinson, Urban background noise affects breeding song frequency and syllable-type composition in the Northern Mockingbird, The Condor, 121:2, (2019).
4. K. D. Frank, Impact of outdoor lighting on moths: an assessment. Journal of the Lepidopterists’ Society. 42, 63–93 (1988).
5. C. M. Stracey, B.Wynn, S.K. Robinson, Light Pollution Allows the Northern Mockingbird (Mimus polyglottos) to Feed Nestlings After Dark. The Wilson Journal of Ornithology. 126:2, 366–369 (2014).