Terrestrial Birds in the Lower Coos Watershed

What’s Happening?

Raptors

This section summarizes the status and trends of raptor populations, including hawks, eagles, and other birds of prey. Regional data are presented at a statewide level using breeding population estimates as a proxy for abundance. A discussion of Coos estuary data, which use Audubon Christmas Bird Count (CBC) sightings to project trends in local raptor abundance, follows (Figure 1). The Local Raptor Trends section describes the status of raptor species that display the most apparent abundance trends since the 1980s.

Statewide Raptor Trends

The United States Geological Survey (USGS) Patuxent (MD) Wildlife Research Center (2014) conducts the North American Breeding Bird Survey (BBS), which includes 144 survey sites in Oregon. One of the Oregon sites is located within the project area and three sites are located near the project area (Figures 1 and 2). This survey is conducted annually along preselected observational “routes.” The BBS data are used here as indices of relative bird species abundance and should not be interpreted as estimates of the total population size (D. Ziolkowski, pers. comm., November 24, 2014).

Figure 3 displays the BBS abundance data for six raptors species that have displayed clear trends (1966-2012) in Oregon. It should be noted that some of these trends are subject to data limitations (e.g., small sample size) that can reduce the reliability of the results. Please see the chapter summary for more information about these limitations.

Local Raptor Trends

Below we focus on raptor species in the Coos estuary that show strong evidence of changing populations:

Osprey (Pandion haliaetus)

From 1980-1997, there were no Osprey sightings in the Coos estuary during the CBC (Audubon 2014, Rodenkirk 2012b, Cornu et al. 2012). However, since 1997, Ospreys have been sighted consistently, with 1-3 birds wintering annually (Audubon 2014; Rodenkirk 2012; T. Rodenkirk, pers. comm., January 19, 2012; Cornu et al. 2012, )(Figure 4).

Figure 6. USGS Patuxent Wildlife Research Center conducts the North American
Breeding Bird Survey (BBS) along observational routes at 144 sites in Oregon
(white), including one site within the study area (yellow). The project area (cross hatch)
has been highlighted for reference. Habitat within proximity to the project area (less than
20 miles) is also highlighted (see Figure 1). Data: USGS 2014

Bald Eagle (Haliaeetus leucocephalus)

Historically, bald eagle populations were in danger of extinction throughout their range, but they have since recovered (USFWS 2013). The CBC data, which show a generally increasing trend of midwinter eagle abundance in the Coos estuary, suggest that the overall recovery of this species may be mirrored by the recovery of local bald eagle populations (Figure 5).

Red-shouldered Hawk (Buteo lineatus)

Red-shouldered hawks were not sighted during the Coos Bay CBC until 1993. Sightings have generally increased since then, averaging nearly 12 sightings annually from 2006-2013 alone (Figure 6).

Other Raptors

Many raptors species are abundant in the Coos estuary, but most of these birds have displayed neither clearly increasing nor clearly decreasing population trends over time. Figure 7 summarizes CBC data for commonly sighted raptors in Coos Bay.

This section discusses trends in owl abundance at a statewide level as well as locally. Emphasis is given to species whose populations have displayed clear trends over time.

The northern spotted owl (Strix occidentalis caurina) and the northern barred owl (Strix varia varia) are mentioned here briefly. Trends for these species are discussed in further detail in the Birds of Special Concern data summary.

Statewide Owl Trends

The great horned owl (Bubo virginianus) is the only owl species surveyed by BBS to exhibit a clear trend (Figure 8). It appears great horned owl populations are decreasing, though the trend is not statistically significant.

Research suggests that the northern barred owl and northern spotted owl have exhibited clear trends at a regional level. Since the early 1990s, the barred owl has expanded its range into southwestern Canada, the northern Rockies, and Pacific Northwest, while the spotted owl has declined throughout its range (Courtney et al. 2004, Davis et al. 2011, Zabel et al. 1996, Forsman et al. 2013).

Owls in the Lower Coos Watershed

Few owl species appear to exhibit either clearly increasing or clearly decreasing population trends in the project area. The exceptions are the northern spotted and barred owls. In upland habitats associated with the lower Coos watershed, spotted owl populations have declined while barred owl populations have grown (Figure 9).

Table 1 summarizes local CBC count data for the most commonly observed owl species. In some cases, the CBC owl species data are relatively sparse, because not all owls are observed every year (e.g., northern saw-whet owl, northern pygmy owl). Available data indicate no clear abundance trend for commonly sighted owl species (Figure 10).

What’s Happening?

Songbirds

This section summarizes data for “passerines,” meaning bird species of the order Passeriformes, commonly referred to as “songbirds.” Songbirds comprise a diverse group of many recognizable bird species (e.g., chickadees, tits, warblers, finches, thrushes, sparrows, etc.). Statewide abundance trends are presented briefly followed by a discussion of local songbird population trends. Emphasis is given to species that have displayed clear trends over time.

Songbirds in Oregon

The BBS indicates that 21 songbird species have shown statistically significant declines since 1966. Only 2 species have had statistically significant increase. Figure 11 summarizes the BBS data for 27 passerine species exhibiting clear population trends in Oregon since 1966.

Songbirds in the Lower Coos Watershed

Below we focus on passerine species in the lower Coos watershed that show strong evidence of changing populations:

Black Pheobe (Sayornis nigricans)

Black pheobes were not sighted during the local CBC from 1980-1995. However, starting in 1996, this species has been sighted every year and has become increasingly abundant (Figure 12).

Common Yellowthroat (Geothlypis trichas)

From 1980-2001, the Coos Bay CBC did not record any common yellowthroat sightings. Since 2002, the species has been sighted in the Coos estuary 5 times during the local CBC, and is now frequently found overwintering in several Coos County locations (Audubon 2014, Rodenkirk 2012)(Figure 13).

Yellow-breasted Chat (Icteria virens)

In 2012, a yellow-breasted chat was sighted at a feeder in Coos Bay, representing the first winter record of this species in Oregon (Cornu et al. 2012). This bird is a neotropical migrant, which means that its midwinter presence may be indicative of a changing climate, although more data are needed to determine if a cause and effect relationship exists (see Why is it happening?)

Cedar Waxwing (Bombycilla cedrorum)

The CBC has sighted cedar waxwings periodically from 1980-2005. However, beginning in 2006, local midwinter sightings have become more consistent and often more frequent (Figure 14).

Swamp Sparrow (Melospiza georgiana)

The local CBC rarely sighted swamp sparrows prior to 1996, but volunteers have recored sightings every year since then (Figure 15).

Red-winged Blackbird (Agelaius phoeniceus)

Red-winged blackbirds are historically abundant in the Coos estuary. This species has been sighted every year during the local CBC since 1980, but the frequency of sightings has increased overtime (Figure 16).

Sparrow species

Many sparrow species have been historically abundant in the Coos estuary. Six sparrow species have been sighted with increasing frequency during the local CBC, including the golden-crowned sparrow (Zonotrichia atricaplillia), house sparrow (Passer domesticus), song sparrow (Melospiza melodia), white-crowned sparrow (Zonotrichia leucophrys), white-throated sparrow (Zonotrichia albicollis), and Lincoln’s sparrow (Mesospiza lincolnii). Summary statistics describing trends in the raw CBC count for these six species are found in Table 2.

American Crow (Corvus brachyrhynchos), Common Raven (Corvus corax), and Stellar’s Jay (Cyanocitta Stelleri)

These three species belong to the family Corvidae and have shown clear increasing trends since 1980. All three birds are historically abundant in the Coos estuary, with multiple sightings occurring every survey year since 1980. CBC sightings are becoming more frequent and may indicate increasing abundance in the project area (Figure 17).

Other Common Songbirds

In addition to the songbird species mentioned above, there are many other passerines commonly found locally. Most of these species do not exhibit a clear abundance trend over time. Table 3 summarizes raw CBC data (1980-2013) for 27 of the most commonly counted songbirds in the lower Coos watershed.

What’s Happening?

This section summarizes data for fowl-like birds of the order Galiformes that are closely associated with terrestrial habitats, including quail, pheasant, grouse, and turkey species. Statewide abundance trends are presented, followed by a discussion of songbird population patterns in the Coos estuary. Emphasis is given to species that have displayed clear trends over time.

Fowl-like Birds in Oregon

The BBS data indicate that two fowl-like bird species, including the wild turkey (Melegris gallopavo) and ring-necked pheasant (Phasianus colchicus), show clear abundance trends (1966-2013)(Figure 18). In Oregon, turkeys are becoming more abundant, while pheasants are becoming less abundant.

Fowl-like birds in the Lower Coos Watershed

The California quail (Callipepla californica) is the only fowl-like bird that is sighted nearly every year during the local CBC. Raw CBC counts for this species indicate no clear abundance trend (Figure 19). In addition to the California quail, ring-necked pheasant and ruffed grouse (Bonasa umbellus) have been sighted on rare occasions (i.e., 1-3 sightings periodically from 1983-2003). Mountain quail (Oreortyx pictus) was counted in 2006-2008 ( < 10 sightings annually). Historically, wild turkeys have not been counted during the local CBC. However, the CBC in 2011, 2012, and 2013 reported 28, 10, and 12 turkey sightings, respectively. More data are needed to determine if these sightings are indicative of a trend (e.g., increasing local abundance or range expansion). Figure 20 summarizes the raw CBC data for all fowl-like birds observed in the study area from 1980-2013.

What’s Happening?

This section summarizes data for birds of the order Columbiformes, which are commonly known as doves and pigeons. Regional data are presented at a statewide level using breeding population estimates as a proxy for abundance, followed by a discussion of Coos estuary data, which use CBC sightings to project trends in local abundance. The local data section highlights dove and pigeon species that display the most apparent trends since the 1980s.

Doves and Pigeons in Oregon

The BBS data indicate that only the mourning dove (Zenaida macroura) shows a clear abundance trend (decreasing abundance) at the regional level (1966-2013)(Figure 21).

Doves and Pigeons in the Coos Estuary

Below we focus on Dove and Pigeon species in the lower Coos watershed that show strong evidence of changing populations:

Eurasian Collared Dove (Streptopelia decaocto)

The Eurasian Collared Dove was first sighted during the CBC in 2007 (Audubon 2014, Rodenkirk 2012). Since then, they have become increasing abundant; CBC sightings have increased notably (Audubon 2014, Rodenkirk 2012)(Figure 22).

Band-tailed Pigeon (Patagioenas fasciata)

Band-tailed pigeons were sighted in three mid-1980s CBC’s and again from 1998-2009 (Aubuon 2014). They have not been counted during the CBC since 2009; scientists indicate they’re very rarely sighted in the winter (Audubon 2014, Rodenkirk 2012).

What’s Happening?

This section summarizes available data for hummingbird species of the order Apodiformes that have shown clear abundance trends either statewide or locally.

Hummingbirds in Oregon

The BBS data show a clear abundance trend over time for the rufous humingbird (Selasphorus rufus), which appears to be decreasing in abundance (Figure 23).

Hummingbirds in the Coos Estuary

Anna’s hummingbird (Calypte anna) is the only hummingbird species regularly sighted during the Coos Bay CBC. The frequency of Anna’s hummingbird midwinter sightings has increased over time, suggesting the species is becoming more locally abundant (Figure 24).

What’s Happening?

This section summarizes available data for birds of the order Piciformes, which are commonly referred to as woodpeckers, sapsuckers, and flickers. The data summary focuses on birds that have shown clear abundance trends either statewide or locally.
Woodpeckers in Oregon

The BBS data indicate that five woodpecker species of have shown clear abundance trends statewide since 1966 (Figure 25). Pileated woodpeckers, yellow-bellied sapsuckers, and re-breasted sapsuckers appear to be increasing in abundance over time, while northern flickers, and red-naped sapsuckers appear to be decreasing in abundance in Oregon.

Woodpeckers in Lower Coos Watershed

Several woodpecker species are commonly sighted in the Coos estuary. However, it’s difficult assess any abundance trends. CBC sightings of some species (e.g., northern flicker) are rare and do not show any apparent trend. Table 4 summarizes the raw CBC data for woodpecker species in the Coos estuary.

Figure 25. BBS abundance data for woodpecker species that have shown clear abundance trends statewide (1966-2013). Data: USGS 2014

Multiple factors can often work together to determine local bird abundance trends (e.g., land use changes occurring simultaneously with climate anomalies may work to the detriment of some species while favoring others). Similar to aquatic birds, some terrestrial bird species are highly migratory. Therefore, factors affecting distant habitats may affect bird species survival rates which will be reflected in local abundance data.

Birds expand their ranges when the resources they rely on for survival become available to them in different geographic areas (Cornu et al. 2012). Habitat alterations related to human activities and climate change are also leading factors in bird range expansions (Askins 2000). This might explain the range expansions of black phoebes and red-shouldered hawks, which have moved northward toward Tillamook County and east to the Williamette Valley over the past 30 years (T. Rodenkirk, pers. comm., January 19, 2012).

Human population growth and urban development may benefit birds in some cases (Cornu et al. 2012). Peery and Henry (2010) explain that “The expansion of human activities into rural areas and natural landscapes has resulted in widespread increases in the abundance of synanthropic species (birds that live near humans and benefit from an association with human habitat).” In fact, some birds that have the ability to adapt to a wide range of habitat conditions (e.g., crows, ravens) have been observed in higher density in urban settings (Kelly et al. 2002). Doves and pigeons are also famously synanthropic species. The Eurasian collared-dove, an introduced species, was first recorded in Oregon in 1999 (Cornu et al. 2012). By 2006, Eurasian collared-doves had established themselves in all 36 Oregon counties, including Coos (R. Namitz, pers. comm., January 19, 2012; T. Rodenkirk, pers. comm., January 19, 2012).

In some cases, active habitat management and restoration have resulted in species recoveries. Similar to the brown pelican (see Aquatic birds), the bald eagle and peregrine falcon have benefited from the efforts of volunteers and avian professionals alike (Cornu et al. 2012). In both cases, the effort has been substantial enough to remove the species from the federal Threatened and Endangered Species List (USFWS 2014).

Some evidence suggests that the overwintering population of neotropical migrants (e.g., common yellowthroats, orange-crowned warblers, and yellow-breasted chats) in Coos County may be increasing (R. Namitz, pers. comm., January 19, 2012; T. Rodenkirk, pers. comm., January 19, 2012; Rodenkirk 2012a; Audubon 2014). Neotropical migrants are birds that spend the summer in the northern temperate and polar latitudes and migrate south to the tropics where climate and food availability is more agreeable in the winter months (Cornu et al. 2012). This trend could be indicative of a general warming pattern in the temperate latitudes, although more data are needed to determine the exact correlation between climate change and neotropical migrant abundance.

Habitats availability also influences local abundance trends. The Coos estuary and associated uplands represent important breeding, foraging, and roosting habitats for many bird species. As habitats are lost or restored, bird distributions may shift to reflect changes in the availability of important resources (e.g., food/prey, cover, etc.) and changes in the presence/absence of predators.

Oregon’s total wildlife diversity accounts for more than 42% of all terrestrial vertebrates in the United States and Canada (Csuti et al. 1997). Birds species comprise much of that diversity; many remain in Oregon year-round and others visiting the state during migration.

Because birds use the lower Coos watershed and estuary for a variety of activities (breeding, nesting, roosting, foraging, etc.), trends in local bird abundance and migration timing can signal important changes to habitat availability or suitability; these habitat changes have the potential to affect both birds and other wildlife (Cornu et al. 2012). Birds can often be considered “indicator species,” because changes in their status can provide an early warning about less detectable trends in local environmental conditions.

Changes in the abundance of one bird species can sometimes directly affect other species. For example, the range expansions of the northern barred owl are likely to negatively affect local populations of northern spotted owls (see Birds of Special Concern data summary in this chapter). However, this kind of direct cause/effect relationship doesn’t always exist. In the case of the Eurasian collared-dove, some concern exists about competitive pressures on native mourning doves (Zenaida macroura). However, research suggests that although the two species have similar diets, the Eurasian collared-dove “does not appear more behaviorally aggressive or competitively successful than mourning doves” (Poling and Hayslette 2006).