Aves (Birds): Ciconiiformes, Falconidae
Merlin (Falco columbarius)
Potential Occurrence: Wintering Unlikely to Occur
Status: (Nonbreeding/Wintering)
Federal: none
State: Watch Listed
Other: G5 S3
Species Description:
Photo: Nick Dunlop
Photo: Nick Dunlop
Small
falcon.
Sexually
dimorphic in size and plumage (adults but not juveniles). Total body length varies from 24 to 30
cm, wing span from 53 to 68 cm, depending on sex and subspecies. Mass: (on average) males
160–170 g; females 220–240 g. Iris dark brown, beak dark blue-gray, and cere and legs bright
yellow (breeding males have noticeably orange legs). Adult males 24% to 30% smaller in body
mass than females, with dorsal plumage varying from blackish gray to pale blue-gray. Undertail
coverts typically whitish with dark feather shafts. Leg feathers often have a distinct rufous wash;
adult males have rufous wash on sides of breast. Tail black with white terminal band; generally 2
(Black Merlin), 3 (Boreal), or 4 (Prairie) lighter bands, usually gray. These bands reduced or
nearly absent in Black Merlins. Females have similar breast pattern, but are brown on the back
and lack rufous leg feathers (rump and uppertail coverts have grayish cast in Boreal Merlins).
Female tail dark brown with buffy to white light bands and a terminal white band. Yearlings of
both sexes resemble adult females in coloration, but are sometimes darker on back (Boreal
subspecies) and lack grayish cast on rump and uppertail coverts. Like adults, yearlings show
reversed sexual size dimorphism (females larger than males). Juvenile females separable from
juvenile males by larger size and more tawny dorsal tail bands; from adult females only in late
summer and fall by lack of molt…Most individuals lack the distinct mustache mark that is typical
of most other North American falcons and are readily distinguished from the American Kestrel by
their lack of rufous coloration on back and tail…(From Warkentin et al 2005)
Distribution: Breeds in Canada and northern US, and is a year around resident in coastal
western Canada and Alaska and northwestern central US (Warkentin et al 2005). This species
is an uncommon winter migrant in California from September to May (Zeiner 1990).
Life History & Threats:
Yearlong, diurnal activity…Winters in California from September to May. Wanders in search of
abundant prey. Some individuals migrate as far as South America in winter….During winter,
mean home range size of adults was observed to be 196 ha in Saskatoon (Warkentin and
Oliphant 1990)….Aparently do not defend feeding territories (Becker and Sieg 1987, Warkentin
and Oliphant 1990, Sodhi and Oliphant 1992). Feeding home range tend to overlap.
Intraspecifically aggressive while nesting…Clutch of 4-5 eggs laid from late May into June.
Incubates 28-32 days, and chicks fledge at about 24 days (Trimble 1972)…Because feeds mostly
on birds, numbers probably have been reduced by pesticides. Potential avian predators are
driven away as soon as they enter the territory; particularly intolerant of accipiters (Fox 1964,
Bent 1938, Oliphant 1974). (From Zeiner et al 1990)
Wintering Merlins feed heavily on various species of small shorebirds in areas where they are
abundant; e.g., Least Sandpiper (Calidris minutilla) and Dunlin (C. alpina) each made up nearly
40% of the diet of Merlins wintering at Bolinas Lagoon (Page and Whitacre 1975; Buchanan et al.
1988). (From Warkentin 2005)
In North America, loss of suitable habitat may be the major factor affecting Merlin numbers (Cade
1982, Oliphant 1985)…The effects of habitat loss and change on… wintering grounds are still
unknown… Although most Merlin populations are no longer affected by pesticide contamination
and are reproducing well (see Demography and Populations: measures of breeding activity),
some individuals may still be impacted…Contaminants remain higher than levels suggested to
cause abnormal behavior (Fox and Donald 1980) … Merlins from North America continue to be
exposed to DDT through prey either on wintering grounds in Central and South America, or via
the prey that they consumed on the breeding grounds (e.g., Schick et al. 1987)... (From
Warkentin 2005)
Habitat & Habitat Associations:
General Wintering Habitat:
Poorly documented, but appears similar to breeding habitat, e.g., open forest and
grasslands…Regularly hunts prey (e.g., shorebirds) concentrated on tidal flats (Page and
Whitacre 1975, Boyce 1985, Buchanan 1988)… Often winters in cities throughout its range,
where frequently perches on buildings, power poles, and tall trees (Oliphant 1974, Servheen
1985, Warkentin and Oliphant 1990). (From Warkentin 2005)
Winters in open woodland, grasslands, open cultivated fields, marshes, estuaries, and seacoasts.
(From Sodhi et al 1993)
Seldom found in heavily wooded areas, or open deserts. Frequents coastlines, open grasslands,
savannahs, woodlands, lakes, wetlands, edges, and early successional stages. Ranges from
annual grasslands to ponderosa pine and montane hardwood-conifer habitats…Frequents open
habitats at low elevation near water and tree stands. Favors coastlines, lakeshores, wetlands.
(From Zeiner et al 1990)
Roosting Habitat:
May roost communally (L. Powers pers. comm.) but usually singly in conifer trees; tall trees with
greater crown volume selected for roosting (Warkentin and James 1990). ( From Warkentin
2005)
Foraging Habitat:
Regularly hunts prey (e.g., shorebirds) concentrated on tidal flats (Page and Whitacre 1975,
Boyce 1985, Buchanan 1988). (From Warkentin 2005)
Frequents shorelines in winter and catches shorebirds. (From Zeiner et al 1990)
Conceptual Basis for GIS Model Development: Potential nonbreeding/wintering habitat in the
Study Area was mapped as:

coniferous forest types (i.e. Redwood-Douglas fir mix (Sequoia sempervirensPseudotsuga menziesii) or Pacific Douglas fir (Pseudotsuga menziesii var.menziesii)
with canopy cover < 40%

cismontane woodland (i.e., mixed hardwoods, montane mixed hardwoodsj, single
dominant hardwoods with canopy cover < 40%)

grasslands

agricultural areas
Potential Occurrence in the Galbreath Wildlands Preserve: Protection status for this species
applies to nonbreeding/wintering individuals.
Habitat: Merlins winter in open woodlands, grasslands, open fields on or near marshes,
estuaries and seacoasts (Sodhi et al 1993). Appropriate seacoast habitat is 15 to 20 miles west
of the Preserve. Merlins, however, are strong fliers and may on occasion visit the Preserves
open woodlands and grasslands. These habitats are patchily distributed in through the center of
the Preserve (Figure 80). More extensive grasslands and agriculture areas are located north of
the Preserve boundaries. It is unlikely that this species would spend much time on the Preserve
due the poor quality of wetland areas where Merlins prefer to forage (e.g., freshwater marshes,
lakes). Areas with emergent vegetation are very rare and riparian vegetation along Rancheria
Creek is poorly developed.
Nearest Occurrence:
Documented Occurrences in the Galbreath Wildlands Preserve: This species has not
been documented on the Preserve. To our knowledge no surveys have been conducted.
Nearest Occurrence to the Galbreath Wildlands Preserve: This species has not been
reported to occur in USGS quads adjacent to the Preserve.
Summary: We anticipate that nonbreeding/wintering Merlins are “Unlikely to Occur” in the
Preserve. Merlins are uncommon winter migrants in California and prefer coastal areas. The
Preserve lacks high quality wetland foraging habitat and location of the Preserve roughly 20
miles inland of preferred winter foraging areas.
References
Sodhi NS, Oliphant LW, James PC, Warkentin IG. 1993. Merlin (Falco columbarius). The Birds
of North America, No. 44. Philadelphia: The Academy of Natural Sciences; Washington, D.C.:
The American Ornithologists' Union.
Warkentin IG, Sodhi NS, Espie RHM, Poole AF, Oliphant LW, James PC. 2005. Merlin (Falco
columbarius),The Birds of North America Online <http://bna.birds.cornell.edu/bna/species/044>.
Accessed 2010 Jul 29.
Zeiner DC, Laudenslayer WF, Mayer JE Jr., and White M, eds. 1988-1990. California's Wildlife.
Vol. I-III. Sacramento: California Depart. of Fish and Game.
Species Account Description: Linden Scheider & Emily Harvey