Endangered and Displaced: The Struggle for Survival of Pennsylvania’s Short-Eared Owls
Photo by Pete Nuij
Pennsylvania’s grasslands, wetlands, expansive old fields have been the cradle of a diverse array of bird species. Among these feathered inhabitants, the short-eared owl, Asio flammeus, holds a particularly precarious position. Endangered within the state, yet under federal protection as a migratory bird, these enigmatic owls find themselves caught in a struggle for survival. The increasing expansion of urban development and agricultural land is steadily eroding their natural habitat, posing a significant threat to their existence. Today, we will explore a plan of action I drafted that looks to take on the challenges faced by the short-eared owls, exploring their habitat requirements, the factors limiting their survival, and the recovery strategies implemented to protect and stabilize their dwindling population. We’ll investigate the intersecting realms of wildlife, environmental policy, and human impact.
Current Status: The short-eared owl, Asio flammeus, is considered an endangered bird species in the state of Pennsylvania (PGC 2014). Short-eared owls are not listed at the federal level for being endangered or threatened. Short-eared owls are a migratory bird and a bird of prey so while they are not considered endangered or threatened at the federal level, they are protected under the Migratory Bird Treaty Act of 1918 (PGC 2014). The status of their habitat is unprotected except for wetland areas. Short-eared owls are ground-nesting birds and with the expansion of urban development and increasing acreage for agriculture, their nesting grounds are threatened.
Habitat requirements and limiting factors: Short-eared owls are a migratory bird that relies on pastures, marshes, wetlands, and hayfields for wintering areas. Since they migrate across multiple locations, their habitat can vary. Most often short-eared owls will inhabit salt and freshwater marshes, tundra prairies, grasslands, old fields, and shrublands (Booms et al. 2014). An abundance of voles and other small mammals is required for an area to be suitable for Short-eared owls to nest and roost (Vukovich et al. 2008). There are a few limiting factors that are involved with short-eared owls inhabiting an area. Urban development has filled in marshes, taken away a significant amount of wetland areas, and reduced the number of small mammals available (PGC 2014). Since short-eared owls prefer open land and nest on the ground, urban settings and “concrete jungles” have restricted the number of migratory spaces for them to inhabit. Hayfields and agricultural lands preferred spots for short-eared owls, along with other bird species, to inhabit. While the land provides a lot of shelters and attracts a significant food source to the area, these areas are not suitable either since the landscape is always being altered.
Recovery objective: Stabilize current populations within the state of Pennsylvania and restore viable populations (95%+ chance of persisting 100 years). The removal of the short-eared owl from Pennsylvania’s Game Commission’s list of endangered species.
Recovery strategy: Protect known and past breeding grounds, utilize abandoned mines as proper nesting and wintering areas.
Recovery Criteria:
An annual increase in state population size to at least 50 per year for 10 years with 40 breeding pairs distributed throughout the state.
Achieve an average fecundity of 3–4 fledglings per year for each breeding pair within 10 years. After the 10-year period models will show a steady growth in the population size.
Expanded protection laws for open areas across the state that were historically nesting and wintering grounds.
State legislation that further protects the habitats of migratory birds from being overtaken for agricultural land use.
Abandoned mines and passive acid mine drainage treatment systems are designed to incorporate constructed and restored open fields and grassland areas that can be used as suitable nesting and wintering areas. Preference will be given in favor of restoration for all abandoned mines if it is deemed to be a suitable habitat by a state wildlife biologist and third-party surveyor.
A 50% increase in small mammal populations in the state, namely varied species of field mice and voles.
State legislation for state parks to construct nesting habitats and wintering areas in unused open areas, with restricted access from park visitors and non-essential personnel working within the park.
Actions needed:
Designate historically sited nest areas as state protected areas while maintaining these areas to increase protection from predation and anthropogenic effects.
Protect the current breeding population and currently active nesting areas in order to maximize fecundity.
Utilize abandoned mines and AMD treatment sites for potential nesting and wintering areas.
Allocate funds to research projects and survey efforts to locate and study the nest areas.
Utilize state parks as a potential refugee for nesting and wintering areas.
Develop partnerships with non-profits in order to raise funds and create opportunities for public education and community outreach programs.
Conduct biannual evaluations on population trends within the state and wintering areas outside the state and revise recovery tasks as needed.
Create predictive models that can provide a timeline of possible extirpation and develop emergency plans in the event extirpation is evident.
Date of Recovery: The date of recovery is based on how successful the conservation measures are. Based on what is known and the potential for success, the short-eared owl could make its way off of the list of endangered species in the state of Pennsylvania by the year 2033 with a full recovery by the year 2043. That is assuming the recovery criteria have been met and support continues past the 10 years. After the 10 years, revisions to the recovery plan are recommended to adjust for the increased numbers in the population.
Introduction
The short-eared owl, Asio flammeus, was designated as an endangered species in Pennsylvania in 1985 as apart of the Species of Special Concern (PGC 2014). It is not listed as at-risk or endangered at the federal level; however, due to the federal Migratory Bird Treaty Act of 1918, they are a federally protected species. A Partners in Flight North American Landbird Conservation Plan also has them designated as a priority grassland species (PGC 2014). While it is not federally listed, the reason for it being listed as endangered in Pennsylvania is due to its relatively small breeding population and small distribution throughout the state. In the 2nd edition of the Pennsylvania Breeding Bird Atlas, between the years 2004–2008, only one nesting ground was discovered (PGC 2014). The total population of short-eared owls is unknown and hard to estimate due to their lack of numbers. It is believed that nationwide, there are about 10,000 short-eared owls. Unfortunately, they have a population decrease >10% each year (PGC 2014).
Species Description:
The short-eared owl is a species of owl that can be found throughout most of the world. It belongs to the genus Asio and is one of few ground-nesting bird species. Short-eared owls range in size from 13–16.9 inches, similar to the size of a crow (PGC 2014). Their wingspan can be anywhere from 33–43 inches and weigh as much as 7–17oz (PGC 2014). Color markings for short-eared owls are fairly distinguished from other owl species. Their facial disk is white, fading into black around its eyes. Their loral bristles and eyebrows are white but can also appear transparent. Their cere, which is a membrane covering over the base of the upper mandible, is brown and usually varies in length (1–1.5 inches). The short-eared owl also has small ear tuffs located near the center of their foreheads. The ear tuffs are not usually visible unless they become excited (Booms et al. 2014).
The nape and crown have yellowish-brownish streaks and are a more distinct feature from the rest of their body. The upper portions of their body are a yellowish-orange color with a slight grey fade. The bottom portion of their body is a pale brown color fading to black around the wrist. This is more noticeable when the owl is in flight. The remaining portions of its feathers are different hues of brown ranging from light to dark. Their underside tends to be white with distinct, brown streaks. Their tail is a wedge shape and measures to be 5–6.1 inches (PGC 2014). Males tend to be smaller (stocky) than the female (taller) but more vibrant. Male short-eared owls have more white and dark brown feathers while females will usually have dark brown and brownish-orange feathers.
Short-eared owls, like many other bird species, have their own unique call. The call of a male tends to sound like a “voo-hoo-hoo” while others interpret the sound as “ooo-choo-choo” which both resemble an old train (Short et al. 1962) . Males use this sound as their territorial song. Being a diurnal species, short-eared owls are generally quiet and will utilize their song mainly while in flight. Females will usually respond with “kee-ow” which resembles a sharp barking noise (Short et al. 1962). When nesting, both the male and female will make several sounds when they become excited in their nest. If disturbed, they will let out a defensive call, “cheeaw” (Short et al. 1962), to alert each other of a potential intruder.
Diet:
There is a strong correlation between nesting and roosting areas and the number of field voles in the vicinity (Vukovich et al. 2008). Short-eared owls are diurnal and search for food within a couple of hundred meters of their nest area. Mornings, late afternoon, and evenings are when they are most likely to be active and hunting. Their tactics for tracking prey is similar to other species of owls and other birds of prey. When searching for prey, they will glide a few feet above open areas and dive when they have spotted their prey (Vukovich et al. 2008). If the vegetation is dense enough, they will sit perched on a branch or hide in the brush on the ground. Short-eared owls handle their prey differently than other species. Often-times, owls will carry their prey in their beaks; however, since the short-eared owl has a small beak, they utilize their claws to carry off prey, similar to an eagle (Vukovich et al. 2008). Short-eared owls tend to eat mainly small mammals such as meadow voles, shrews, ground squirrels, gophers, moles, bats, rabbits, muskrats, and even other small birds (Booms et al. 2014). Meadow voles tend to be the most favored small mammal that they prefer. The hunting of other birds tends to usually occur in coastal areas and salt marshes where there is an absence of small mammals. Short-eared owls don’t hunt without competition. Often short-eared owls must compete with Northern Harriers for food (Vukovich et al. 2008). In some instances, they will fight each other resulting in injury or fatality to both species. Northern Harriers tend to be larger than short-eared owls and often steal food from them without much of an incident, though in the event a fight breaks out, it can be a deadly encounter. During mating season, and when eggs have been laid, the male short-eared owl will be responsible for providing food to the female and the offspring (Lockie JD 1955). During this period, the male will venture slightly further away from its nest to hunt, avoiding bringing attention to the nesting spot. As the male hunts, the female will incubate the eggs and protect the nesting area.
Reproduction:
It is rare and difficult to find a nesting site for the short-eared owl. Fortunately, their courtship rituals have been observed in past studies and surveys. Breeding season for short-eared owls begins in March and ends in June (PGC 20014). Like other birds of prey, the male will perform an aerial display to entice the females. The display is rhythmic with flagrant wing beats. The male will move in a series of sequences from hovering, to gliding down towards the ground and flying upwards again (Lockie JD 1955). This display of courtship by the male occurs anywhere from 200 to 400 meters above the ground. Vocalization occurs throughout the male’s cadence and will bring its wings together as if it is clapping, in rapid succession. The end of its courtship dance occurs when the male descends towards the ground (Lockie JD 1955). Often times the female will engage with the male and lock talons with him and ascend upwards in the air. The results of this behavior might simulate a fight; however, neither birds are injured in the process.
If the male’s courtship is successful, the two will nest together. Short-eared owls are unlike other bird species in that they are a ground-nesting species. Their nest will usually be located under tufts of grass, shrubs, or tall grass. The female will construct the nest from various vegetation and their feathers that they pluck from their breast (Lockie JD 1955). The size of the clutch can vary from year to year depending on the amount of food available around the nesting area. Short-eared owls can lay as many as 4 to 14 eggs with the average being 5 to 7. There is a geographic correlation for clutch sizes, with them increasing the further north you go (Booms et al. 2014). Eggs will be laid every day or two with incubation occurring after the first egg is laid. The incubation period for the eggs is around 1 month. Short-eared owls will lay replacement eggs since predation is high for them. Often, a female can lay 2 sets of clutches within a year (Lockie JD 1955). The male is primarily responsible for providing food while the female is responsible for protecting the nest and incubating the eggs. The male will take turns every so often in incubating. Once the eggs hatch, it only takes about 12 days for the fledglings to begin moving from the nest and 4 weeks before they are young fledglings. This is a remarkable adaption for ground-nesting birds since the risk for predation is so high. Short-eared owls are rare breeders and have been limited to the St. Lawrence Valley, Lake Champlain Valley, Great Lakes plans, and the marshlands along Long Island’s south shore (Vukovich et al. 2008). Nest from previous years are often reused by other short-eared owls; however, it is not known if it is always by the same owl.
Habitat, Range, Distribution, and Taxonomy:
The short-eared owl inhabits a wide range of areas. Most areas that are favored by short-eared owls tend to be wide open spaces such as inhabited salt and freshwater marshes, tundras, prairies, grasslands, old fields, estuaries, and shrublands (Lockie JD 1955). Areas that they will inhabit are often dictated by the number of small mammals located in the area. If it lacks a necessary food source, it will continue to search for other locations for food (Short et al. 1962). The most important characteristic of the short-eared owl’s habitat is ground coverage. Since they are a ground-nesting species, they rely on ground coverage for survival. They will most often roost and nest on the ground under shrubs, tufts of grass, logs, and among tall grass under trees.
They also rely on ground coverage to help conceal their source of small mammals for food. Short-eared owls are considered nomads since they often move to multiple locations during the migration season. It is during the winter months that short-eared owls will inhabit the aforementioned areas; these spots are known as a wintering area. Short-eared owls can be territorial up to 6 hectares during winter months and increase that to up to 200 hectares during the breeding season; however, they can form large communal roosts (Booms et al. 2014). While it is sometimes atypical for a bird species to migrate out of the migration season, short-eared owls will abandon winter sites with a low abundance of food and migrate to a different area (Lockie JD. 1955). If the wintering area proves to be fruitful, many short-eared owls will remain at the wintering site and use it as their breeding grounds while others will migrate further north to the different breeding sites. Wintering sites are important for short-eared owls survival as unsuitable habitats will lead them to seek shelter in unconventional locations such as farmlands and airports where they have recorded high mortality rates (Boom et al. 2014).
The short-eared owl’s range and distribution are vast. They inhabit most continents, except for Antarctica and Australia, and are distributed throughout their respective regions (Boom et al. 2014). Their range makes them one of the largest distributed birds in the world. There are 10 known subspecies of the short-eared owl. The A. f. bogotensis, A. f. domingensis, A. f. flammeus, A. f. galapagoensis, A. f. pallidicaudus, A. f. ponapensis, A. f. portoricensis, A. f. sandwichensis, A. f. sanfordi, A. f. suinda. are the ten recognized subspecies of the short-eared owl. A.F. flammeus is the subspecies native to North America. What each of these subspecies have in common is that they are all migratory birds. An unconfirmed subspecies, A.f. cubensis was found in Cuba but has not been officially recognized (Boom et al. 2014). A.f. flammeus is the most common subspecies, populating Europe, Asia, America (North and South), the Caribbean, Hawaii, and the Galapagos (Village A. 1987). Data is limited as to whether A.f. flammeus migrates between large geographic regions since they have only been observed to be semi-migrants (travels only a limited distance between breeding and winter grounds). The main difference between the subspecies was size and coloration (Boom et al 2014). These differences are most likely a result of evolutionary adaptations to specific regions to survive. For example, short-eared owls found in tropical regions were smaller and more vibrant than those found in the northern hemisphere. It was also observed that the subspecies in the southern hemisphere varied in beak size.
Reasons For Listing:
The short-eared owl is listed in Pennsylvania as endangered. Over the years, suitable habitat for wintering and nesting has been lost. Habitat loss is attributed to urban development, new aggressive agriculture practices, or natural succession in which previously opened fields convert back to the forest (PCG 2014). Short-eared owls are now considered rare breeders, limited to specific areas that are untouched (Booms et al. 2014). The population in Pennsylvania, and many other states, have decreased due to short-eared owls moving further north into Canada and the Great Lakes areas in search of suitable breeding and wintering habitats (Village A. 1987). A large portion of Pennsylvania’s open lands is used for agriculture or industrial operations (natural gas drilling, quarries, mines, mills). While they are not on the federal list for endangered species or species of concern, they are protected under the federal Migratory Bird Treaty Act of 1918.
While the short-eared owl is most effected by anthropogenic effects, natural predation compounds with human activity in reducing their population size. Since short-eared owls are ground nesters, they are open to predation by several predators. The most common predators to the short-eared owl are eagles, coyotes, foxes, snowy owl, northern harrier, and red-tailed hawks (Brooms et al. 2014). Other scavengers tend to steal their eggs, further effecting their reproductive rates. As the population size of coyotes continues to increase in Pennsylvania, conservation efforts for short-eared owls will become more challenging.
Current Conservation Methods:
As of now, there are no conservation plans for the short-eared owl in Pennsylvania. While the state has deemed the short-eared owl as endangered, conservation efforts are hard for migratory birds, especially for those with a small breeding population. Only a hand full of nesting areas have been found in the state and there is limited evidence that suggests they are reused by the same group (PGC 2014). This hinders the state’s ability to put in place adequate measures to protect breeding grounds. Conservation laws make it clear that development cannot occur if a protected species is inhabiting the area; however, short-eared owls do not always reside in a single area or return, nor are their nest easy to find. As a result, what might have once been a breeding ground for them is turned into an industrial complex or housing. As of now, the closest conservation tool the state has in a place that benefits the short-eared owl is the protection of wetland areas.
Recovery
Recovery objective: Stabilize current populations within the state of Pennsylvania and restoring a viable population (95%+ chance of persisting 100 years). The removal of the short-eared owl from Pennsylvania’s Game Commission’s list of endangered species.
Recovery Criteria:
To have the short-eared owl moved from being endangered to threatened, at least seven criteria must be met in ordered to deem the conservation efforts as successful. First, there must be an annual increase in state population size by 50 each year for 10 consecutive years. Also, there must be at least 40 breeding pairs distributed throughout the state. Second, the population must achieve at least a fecundity of 3–4 fledglings per year for each breeding pair within the 10 years. Since short-eared owls tend to have a clutch of 4–7 eggs on average and will often spawn eggs twice in a season, a fecundity of 3–4 fledglings assumes about a 50% survival rate of offspring among mating pairs. Also, after the 10-year period modeled data must show steady growth in population size. This will further support the notion that conservation methods are successful.
Pennsylvania has about 22 million acres of forested area and open land. The third criteria that must be fulfilled are the expansion of land protection laws for open areas across the state that have been historically used for nesting and wintering grounds. While there is little data to suggest that short-eared owls will habitually return to former nesting grounds, protecting the land so others that are migrating is important in providing suitable habitat for breeding. Agriculture and urban developments are the leading cause of habitat loss in Pennsylvania as more of the open land areas (marshes, abandoned mines, grasslands) are being acquired for developmental purposes (PGC 2014). The fourth criterion for recovery will require state legislation that further protects the habitats of migratory birds from being overtaken for agricultural land use and urban development. This not only benefits the short-eared owl but also many other migratory birds affected by habitat loss.
Due to Pennsylvania’s rich industrial history, it now has 11,290 abandoned mines with roughly 9,862 of those mines contributing to environmental damages through acid mine drainage (AMD). It has been observed in the past that short-eared owls will nest in abandoned mine areas due to the low disturbance levels (Brenner et al. 2007). The fifth criterion would require abandoned mines and passive acid mine drainage treatment systems to be designed to incorporate constructed and restored open fields and grassland areas that can be used as a suitable nesting and wintering area. Preference must be given in favor of short-eared owls if the abandoned mine or AMD site is deemed a suitable habitat by a state wildlife biologist and third-party surveyor. Often times abandoned mines are reclaimed and used for urban development; however, if short-eared owls are utilizing these areas for nesting and winter, it is important to take the opportunity and repurpose these areas for conservation.
Short-eared owls’ nesting sites correlate with rodent populations (Village A. 1987). To ensure adequate nesting areas and to maximize clutch sizes, the sixth criteria will require that there is evidence of at least a 50% increase in small mammal populations in the state, namely varied species of field mice and voles. The seventh criterion is tied to utilizing Pennsylvania state parks. Pennsylvania has 121 state parks as of 2016 and is distributed throughout the state. State legislation that would require parks to construct nesting habitats and wintering areas in unused open areas would ensure a safe area for short-eared owls to nest and allow for areas to become frequent sites of nesting. The areas within the state park must have restricted access from park visitors and non-essential personnel working within the park. Limiting the number of people accessing the open areas where the constructed nesting and wintering areas are located will reduce the disturbance levels and provide the ideal habitat for them to live. While it is not ideal to modify areas within a state park, it should be deemed a necessary evil to preserve biodiversity.
Proposed Recovery Action:
For conservation efforts to be successful, actions by the state must precede before the recovery criteria can be met. First, areas that have been historically documented as nest areas should be protected while also being maintained to increase protection from predation and anthropogenic effects. While the true number of short-eared owls is unknown, it is important to also protect the current breeding population. Also, the protection of currently active and newly established nesting areas will be highly important in maximizing fecundity. The beginning steps of conserving and improving the population numbers will be slow but as the population increases, it will become easier to locate new nesting areas. It will be of great importance for the state to allocate funds to research projects and survey efforts to locate and study nesting areas. With increase research funding and wildlife surveys, it will make conservation efforts more numeric and easier to keep track of. It will also allow the state to designate specified areas of protection before development occurs.
State parks are used for numerous conservation projects and are created specifically to preserve biodiversity. State parks are safe from anthropogenic disturbances that have plagued the short-eared owl over the last several decades. State parks are the much-needed opportunity to potentially establish suitable habitats and small breeding populations throughout the state by creating designated nesting and wintering areas within the parks. Public awareness and funding are crucial to conservation efforts. Developing a partnership with non-profits to raise funds and create opportunities for public education. Not only will these put more money towards conservation efforts but bring awareness to a lesser-known state-designated endangered species. To get accurate numbers and provide reasonable assurance that conservation efforts are effective, biannual evaluations on the population trends within the state and wintering areas outside of the state will be required. Within the 10 years, the recovery task will most likely need to be revised to accommodate trends in the changing population. Having reliable numbers will ensure that what is being reported is the most recent and relevant. It will also allow researchers and surveyors to hone in on specific locations of concern or adapt their research methods to whatever changes might occur. In the event, all efforts to conserve the short-eared owl fail, the development of a predictive model that can provide a time-line for the possibility of extirpation of the species will be important in developing an emergency plan if it is clear extirpation is evident. While conservation methods might have failed, captive breeding programs can be established to hopefully increase the breeding population if it is seen to have fallen to a point in which efforts in the wild have failed.
Literature cited
Brenner FJ. Impact Of The Surface Mining Control And Reclamation Act On Species Of Special Concern In Pennsylvania. Journal American Society of Mining and Reclamation. 2007;2007(1):79–86. doi:10.21000/jasmr07010079
Booms TL, Holroyd GL, Gahbauer MA, Trefry HE, Wiggins DA, Holt DW, Johnson JA, Lewis SB, Larson MD, Keyes KL, et al. Assessing the status and conservation priorities of the short-eared owl in North America. The Journal of Wildlife Management. 2014;78(5):772–778. doi:10.1002/jwmg.719
Lockie JD. The Breeding Habits and Food of Short-Eared Owls after a Vole Plague. Bird Study. 1955;2(2):53–69. doi:10.1080/00063655509475812
Pearson OP, Pearson AK. Owl Predation in Pennsylvania, with Notes on the Small Mammals of Delaware County. Journal of Mammalogy. 1947;28(2):137. doi:10.2307/1375455
Short-Eared Owl. Pennsylvania Game Commission (PGC). [accessed 2020 Jun 18]. https://www.pgc.pa.gov/Wildlife/EndangeredandThreatened/Pages/Short-EaredOwl.aspx
Short HL, Drew LC. Observations Concerning Behavior, Feeding, and Pellets of Short-Eared Owls. American Midland Naturalist. 1962;67(2):424. doi:10.2307/2422718
Village A. Numbers, Territory-Size and Turnover of Short-Eared Owls Asio flammeus in Relation to Vole Abundance. Ornis Scandinavica. 1987;18(3):198. doi:10.2307/3676767
Vukovich M, Ritchison G. Foraging Behavior of Short-eared Owls and Northern Harriers on a Reclaimed Surface Mine in Kentucky. Southeastern Naturalist. 2008;7(1):1–10. doi:10.1656/1528–7092(2008)7[1:fbosoa]2.0.co;2
Village A. Numbers, Territory-Size and Turnover of Short-Eared Owls Asio flammeus in Relation to Vole Abundance. Ornis Scandinavica. 1987;18(3):198. doi:10.2307/3676767
Vukovich M, Ritchison G. Foraging Behavior of Short-eared Owls and Northern Harriers on a Reclaimed Surface Mine in Kentucky. Southeastern Naturalist. 2008;7(1):1–10. doi:10.1656/1528–7092(2008)7[1:fbosoa]2.0.co;2
