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Merlin (Falco columbarius) Potential Occurrence: Wintering Unlikely to Occur


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Aves (Birds): Ciconiiformes, Falconidae

Merlin (Falco columbarius)

Potential Occurrence: Wintering Unlikely to Occur



Status: (Nonbreeding/Wintering)

Federal: none

State: Watch Listed

Other: G5 S3



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Photo: Nick Dunlop

Photo: Nick Dunlop
pecies Description:

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 sempervirens-Pseudotsuga 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 . 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


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