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Eastern Screech-Owl

Megascops asio
Overview
Minnesota Seasonal Status:

A regular, year-round resident, the Eastern Screech-Owl was a rare species during the Minnesota Breeding Bird Atlas (MNBBA).

North American Breeding Distribution and Relative Abundance:

The Eastern Screech-Owl is largely an inhabitant of the eastern deciduous forest from the Mississippi River east to the Atlantic Coast. In the Great Plains it is restricted to scattered woodlots and wooded riparian corridors bordering rivers and streams. Widely dispersed throughout its range, it is rarely present in high densities (Figure 1). In the southern Great Plains, the ranges of the Western Screech-Owl and Eastern Screech-Owl are either close to one another or actually overlap.

Conservation Concern:
Conservation Status Score 10

Assigned a Continental Concern Score of 10/20 by Partners in Flight.

Life History
Migration:

A permanent resident. Some have suggested that northern populations may move south during the winter months, but this is likely a response to winter food shortages.

Food:

An efficient, opportunistic predator that consumes a wide array of invertebrates and small vertebrates. A nocturnal predator, daytime is largely spent roosting in cavities or perched in a tree in dense cover.

Nest:

Cavity nester that uses natural cavities, abandoned woodpecker cavities, and artificial nest boxes.

Eastern Screech-Owl Eastern Screech-Owl. Megascops asio
© Mike Lentz
Figure 1.

Breeding distribution and relative abundance of the Eastern Screech-Owl in North America based on the federal Breeding Bird Survey from 2011 to 2015 (Sauer et al. 2017).

Minnesota Breeding Bird Distribution*

When Roberts (1932) prepared his account of the Eastern Screech-Owl in Minnesota, he described it as a common resident that bred throughout the state. At the time, breeding records were available from five counties: Pipestone (brood out of nest and able to fly); Rice (brood of fledglings); Hennepin (nest); Grant (downy young out of nest); and Polk (nest). Roberts often made sweeping generalizations regarding a species’ distribution. In this case there were no records from north-central or northeastern Minnesota.

Indeed, in 1975 Green and Janssen reported that the species occurred throughout much of the state but, with the exception of a few observations, was “probably a rare resident from Roseau to Carlton counties.” And, other than a few records from southern St. Louis County, it was absent from Cook, Lake, Koochiching, and Itasca counties.” Special note was made of the species’ decline in abundance since the 1960s.

A few years later, Janssen (1987) summarized the owl’s status as primarily restricted to the southern half of the state. Scattered records continued to be reported further north, including a breeding record in Otter Tail County, but the majority of records were from counties south of a line from the east metro region west to Lac qui Parle County. Since 1970, nesting had been confirmed in a total of 17 counties. Hertzel and Janssen (1998) would later add an additional six counties to that list, all from Wadena County south.

Although field biologists with the Minnesota Biological Survey have been conducting intensive bird surveys throughout the state since the late 1980s, nocturnal surveys for owls have not been a focus of their efforts. As a result, only two breeding season locations of the Eastern Screech-Owl have been documented by the survey, both located in southwestern Minnesota (Minnesota Department of Natural Resources 2016).

During the MNBBA, observers reported a total of 64 records of the Eastern Screech-Owl from 1.2% (58/4,743) of the surveyed atlas blocks and 1.2% (28/2,337) of the priority blocks. Breeding was confirmed in 12 blocks (Figures 2 and 3; Table 1). These birds were observed in 36 of Minnesota’s 87 counties (5 of the counties were included because blocks straddled county lines) and breeding was confirmed in 14 counties (3 blocks with confirmed nesting straddled two counties each: Stearns/Morrison, Hennepin/Dakota, and Mower/Olmstead). Seven of the counties were additions to the list published by Hertzel and Janssen (1998): Anoka, Houston, McLeod, Morrison, Mower, Pipestone, and Wabasha. The majority of records were located from the southern two-thirds of the state, from Lake Mille Lacs south to the Iowa border. A few scattered records from the northern regions were restricted largely to northwestern Minnesota. Breeding was most frequently reported from the southern portion of Minnesota’s Eastern Broadleaf Forest Province.

Overall, it seems that the Eastern Screech-owl’s distribution in the state has changed little during the past 100 years. It remains unclear, however, just how common they were in the northwestern and north-central regions in earlier times. Today they are quite rare in these regions; only five MNBBA records were documented north of southern Aitkin County.

The owl’s abundance, however, appears to have declined significantly. Roberts (1932) described it as the commonest member of its family in Minnesota. Wherever there is a growth of trees, even if only a small grove out on the prairie, it may be expected to make its home.” Today, it is a rare sight to come across the bird. Areas where its distinctive nighttime tremolo was commonly heard are now silent. During the MNBBA, the screech-owl was far outnumbered by the Barred Owl, the Great Horned Owl, and the Northern Saw-whet Owl. Even the Great Gray Owl, which was not known as a nesting species in the early 1900s, outnumbered the Eastern Screech-Owl with 83 reports.

Elsewhere in North America, the species has actually expanded its breeding range, especially in Canada. Ritchison and his colleagues noted recent expansions to the northwest across the Canadian Prairie Provinces, north in Manitoba, and east in Ontario. They suggested that urbanization, which is often accompanied by more tree plantings, and warming temperatures may be facilitating these changes (Ritchison et al. 2017). Atlases conducted in other states and provinces showed mixed results. Ontario, for example, documented a significant increase in records between its first and second atlases but also developed a targeted survey for screech-owls and extended its period for acceptable observations during the second atlas (Cadman et al. 2007). Iowa, on the other hand, reported a significant decline in observations between atlases (Iowa Ornithologists’ Union 2017). Michigan witnessed little change but did note a slight retraction on the northern edge of the species’ breeding range in the state (Chartier et al. 2013). In his comprehensive review of Wisconsin birds, Robbins (1991) noted that the northern edge of the species’ range had receded since the 1930s and 1940s in the far northern reaches of the state and in the central regions in the 1960s and 1970s. Given that cold winter weather can be a factor that limits the Eastern Screech-Owl’s northern distribution, Cutright and his colleagues (2006) suggested that the species’ presence in northern Wisconsin may vacillate in response to “mini-climatic” changes over long periods of time.

*Note that the definition of confirmed nesting of a species is different for Breeding Bird Atlas projects, including the definition used by the Minnesota Breeding Bird Atlas, compared with a more restrictive definition used by the Minnesota Ornithologists’ Union. For details see the Data Methods Section.

Figure 2.

Breeding distribution of the Eastern Screech-Owl in Minnesota based on the Breeding Bird Atlas (2009 – 2013).

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Figure 3.

Summary statistics of observations by breeding status category for the Eastern Screech-Owl in Minnesota based on all blocks (each 5 km x 5 km) surveyed during the Breeding Bird Atlas (2009-2013).

Breeding statusBlocks (%)Priority Blocks (%)
Confirmed12 (0.3%)5 (0.2%)
Probable11 (0.2%)6 (0.3%)
Possible33 (0.7%)16 (0.7%)
Observed2 (0.0%)1 (0.0%)
Total58 (1.2%)28 (1.2%)
Table 1.

Summary statistics for the Eastern Screech-Owl observations by breeding status category for all blocks and priority blocks (each 5 km x 5 km) surveyed during the Minnesota Breeding Bird Atlas (2009-2013).

Breeding Habitat

The Eastern Screech-Owl requires woodlands with sufficient mature trees to provide a rich supply of the cavities it depends on. In Minnesota the birds are found in oak forests and woodlots as well as in farmlands and urban settings with large shade trees (Figure 4). It avoids large tracts of dense, contiguous forest and areas with too much conifer cover (Danz et al. 2007). An open understory facilitates foraging and accommodates the bird’s swooping, U-shaped flight pattern, where it makes a steep dive down from its perch and then flies at a level grade until rising steeply to another perch or cavity (Ritchison et al. 2017).

Danz et al. (2007) suggested that the species fares best when mature woodlands are adjacent to forest edges or include gaps in the forest canopy that provide additional foraging opportunities. When openings become less available the habitat becomes more suitable for Barred Owls and Great Horned Owls. Because both of these species are also predators of the smaller Eastern Screech-Owl, some have suggested that forest openings and an open understory may facilitate predator detection (Ritchison et al. 2017).

Figure 4.

Typical breeding habitat of the Eastern Screech-Owl in Minnesota (© Lee A. Pfannmuller).

Population Abundance

Monitoring data collected by the federal Breeding Bird Survey (BBS) from 1966-2015 have been used to generate a North American population estimate of 680,000 breeding adults (Rosenberg et al. 2016). Only a few years earlier, the estimate was 900,000 (Partners in Flight Science Committee 2013). Because screech-owls only have been detected on six occasions on Minnesota BBS routes, the number was too low to generate a statewide population estimate (Sauer et al. 2017).

At the local scale, densities of breeding pairs were reported to be 0.1 to 0.6/km2 in rural Connecticut and in rural landscapes in the Midwest. Further south, in Texas, densities as high as 4.4 to 7.4 pairs/km2 were reported in suburban localities (Ritchison et al. 2017).

The species’ low detectability on Minnesota BBS routes is not unique. No single state, province, or ecological region has an average number of birds detected per route per year that exceeds 0.08. The BBS protocol is designed for diurnal songbirds, not nocturnal owls. Only common species that occasionally call in the pre-dawn hours of the survey, such as Barred Owls and Great Horned Owls, are usually detected but even then at very low rates. As a result, projected population trends have little statistical reliability, even survey-wide (Sauer et al. 2017).

The Western Great Lakes Owl Monitoring program, conducted from 2005 to 2014, was organized by the Hawk Ridge Bird Observatory and was one of the few projects designed to improve monitoring efforts. Surveys were conducted by volunteers during the first two weeks of April, beginning at least one half hour after sunset. Each route consisted of ten stops located approximately one mile apart. Although coverage was intended to be statewide, more routes were conducted in east-central and northeastern Minnesota than elsewhere in the state.

In the 2014 breeding season, a total of 81 routes were surveyed in Minnesota. Eastern Screech‑Owls were not detected on any of the routes. By comparison, 69 routes were surveyed in Wisconsin and screech-owls were detected on 10 of the routes (Grosshuesch and Brady 2015). The annual results since 2005 are depicted in Figure 5.

Whether or not the Eastern Screech-Owl is declining is a matter of some debate given the current monitoring data. Based on the limited BBS data available, biologists have estimated the species has declined 41% since 1970 across North America (Rosenberg et al. 2016). Ritchison et al. (2017), however, suggested that biologists are confusing declines with population cycles, which were documented in the only long-term study conducted in Texas. He asserted that the species has demonstrated a fairly stable population.

Relative to populations in Minnesota, anecdotal evidence suggest a statewide decline in numbers. The only numerical data that points to the bird having declined since the mid-twentieth century is the BBS data from Minnesota. When the survey began in 1967, screech-owls were reported the first three consecutive years of the survey: in 1966 (one bird); in 1967 (two birds), and in 1968 (one bird). During the next 50 years, from 1969 to 2015, there were only two reports: one in 1976 and one in 1995 (Sauer et al. 2017).

It remains unclear if the apparent decrease in the species’ abundance in Minnesota reflects a cyclic fluctuation in response to prey abundance, a more permanent decline in response to irreversible habitat changes, increased competition for suitable nest cavities, or other unknown factors. The species adaptability to urban and suburban landscapes would suggest that increased residential development would positively impact local populations.  Studies in Texas, for example, demonstrated that populations residing in urban and suburban habitats were more stable and reproductively successful than populations residing in rural areas (Gehlbach 1994).  On the other hand, increased populations of species that prey on adult and young screech-owls, including both Barred Owls and Great Horned Owls, could result in local declines.  As the MNBBA data illustrate, both predators were nearly twelve times more abundant than the Eastern Screech-Owl.

Figure 5.

Mean Number of Eastern Screech-Owls per Route for Minnesota and Wisconsin, as detected in the Western Great Lakes Owl Monitoring program (Grosshuesch and Brady 2015).

Conservation

Although it has a large breeding range, concern regarding its apparent population decline and relatively small population size influenced the species moderate Continental Concern Score of 10/20 by Partners in Flight (Rosenberg et al. 2016). The species, however, has adapted well to human-dominated landscapes, leading Ritchison and his colleagues (2017) to conclude that “Long-term negative human impacts on this species as a whole are doubtful.” With the prospect of warming temperatures in the years ahead, the screech-owl also has been rated as having a low vulnerability to climate change (North American Bird Conservation Initiative, U.S. Committee 2010). Indeed, warming temperatures are predicted to further facilitate the species range expansion northward.

Efforts to protect and restore local populations should focus primarily on the retention of mature trees and nesting cavities in deciduous woodlots adjacent to open areas. Nest boxes are an effective tool for encouraging occupation of younger forests, where cavities may be lacking, but proper maintenance of nest boxes is strongly encouraged.

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  • Sauer, John R., Daniel K. Niven, James E. Hines, David J. Ziolkowski Jr., Keith L. Pardieck, Jane E. Fallon, and William A. Link. 2017. The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 12.23.2015. Laurel, MD: U.S. Geological Survey Patuxent Wildlife Research Center. https://www.mbr-pwrc.usgs.gov/bbs/