Magnolia Warbler (Dendroica magnolia)

Magnolia WarblerMagnolia Warbler distribution map

Status/Protection

Population Information

The Federal BBS information can be obtained at http://www.mbr-pwrc.usgs.gov/bbs/bbs.html by clicking on Trend Estimates and selecting the species in question. All estimates are for time period (1966-2005).

Life History

Habitat Selection

During the breeding season, the Magnolia Warbler chooses dense, upland stands of young balsam firs, spruces, white pines, and hemlocks, in both coniferous and mixed forests. Pearson and Niemi (2000) describe MAWA as being strongly correlated with young balsam fir stands, and young conifer stands generally, in areas of trees 5-10 meters (16-32 feet) in height.Nests are poorly-built cups of grasses and other plant stalks with a base of twigs. Nests are positioned on horizontal branches usually near the trunk of a small tree, (but sometimes further out on a branch), and 0.15 to 10 meters (0.5 to 32.5 feet) above ground, although usually below 3 meters (10 feet) above ground. If initial broods are lost or fail, second nesting attempts are not uncommon. Unlike several other warbler species (Blackburnian and Black-throated Green Warblers) typical of conifer forests, Magnolias nearly always choose to nest in low conifers instead of high in the canopy (Hall 1994).

Habitat Availability

Magnolia Warbler is associated with “intermediate stages of coniferous forest regeneration” (Pearson and Niemi 2000, p. 90). Although conifer forest regeneration is low is some areas, and spruce-fir as a forest type has declined in northern WI since presettlement times (Snetsinger and Ventura n.d.), there is apparently sufficient habitat for this species in northern WI, since population information (see section above) demonstrates that this species seems to be increasing in WI. MAWA is mostly found breeding in WI in the northern two tiers of WI counties (see WBBA map, above). Magnolia Warbler is found in boreal forest in WI (Mossman et al. 1990). Although it is present in some other habitat types, it is generally uncommon to rare in northern mesic forests that lack a conifer understory, (Hoffman 1989) and northern swamps and bogs (Hoffman and Mossman 1993). It is a common species on some of the Apostle Islands, (Temple and Harris 1985) with especially high numbers found on North Twin Island (Mossman et al. 1990, Temple and Harris 1985).

Population Concerns

Some increases in population numbers for this species are noted (Hall 1994). An 18.6 % increase (p<0.10) is described for the period 1984-1993 (Price et al. 1995), and a 2.1 %/year increase (P=0.06) is given for Bird Conservation Region 12, with populations in WI showing increases also (see Population Information section, above). Local declines have been noted in areas after spruce-budworm outbreaks, perhaps due to competition with budworm specialist species (Askins 2000). On the whole, clearcut areas that show conifer regeneration can support healthy populations of MAWA, but as trees mature, habitat becomes less favorable to this species (Hall 1994). Askins (2000) states that areas in ME that had experienced damage due to spruce-budworm infestations had subsequent increases in Magnolia Warblers in the years post-infestation, due to dense young conifer regrowth.

Recommended Management

Magnolia Warbler is most common in areas of conifer regeneration, and especially in stands containing balsam fir. Because it is very shade tolerant and requires little or no seedbed disturbance to become established, balsam fir naturally regenerates in the understory of many forest cover types in northern Wisconsin. This dense understory fir component provides important nesting habitat for the Magnolia Warbler and can be fairly easily obtained when a fir seed source is present. Providing this habitat is the best strategy for managing for this species (Pearson and Niemi 2000). Within deciduous forests, removal of all conifers as part of clearcut regeneration harvests will have a negative impact on habitat for MAWA and other conifer-dependent species. Use of a system involving “partial cutting with an extended rotation and a two-phase cutting cycle” (Pearson and Niemi 2000, p. 93) would help to retain conifers. This type of partial cutting should especially encourage balsam fir and white spruce regeneration in both deciduous and mixed stands and will provide breeding habitat to benefit the Magnolia Warbler (Mladenoff and Pastor 1993).

Research Needs

As with numerous other forest birds in the Midwest, data on reproductive success is needed for the Magnolia Warbler. Monitoring and evaluating forestry techniques that encourage habitat for this and other fir-spruce bird species would inform conservation efforts. Additional research needs include study of cowbird parasitism on this species (Hall 1994).

Information Sources

References

Contact Info

Kreitinger, K., Y. Steele and A. Paulios, editors. 2013.
The Wisconsin All-bird Conservation Plan, Version 2.0. Wisconsin Bird Conservation Initiative.
Wisconsin Department of Natural Resources. Madison, WI.

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