Download Bird community changes and habitat succession

Bird community changes and habitat succession: How does the restoration of the
Cache River Wetlands affect the avian communities?
Fran Wachter
PLB 570 Interdisciplinary Science Seminar Spring 2012
INTRODUCTION
In the Midwestern United States, fragmentation of once large and continuous tracts of
bottomland hardwood forests has significantly decreased wetland habitat available to
avian communities. (Andren, 1994) Restoration efforts to remediate this habitat loss often
rely on the processes of succession for reforestation to gradually connect and enlarge
existing tracts of bottomland forests. Since restoration began in the bottomland forests of
Cache River Wetlands and the Cypress Creek National Wildlife Refuge in Southern
Illinois in the 1990’s, biologists have been studying the relationship between forest
fragmentation, avian communities and nest predation of the neo-tropical migratory
songbirds that breed in the wetland (e.g. the Prothonotary warbler) (Hoover, 2009).
Additionally, Brown-headed cowbirds parasitize the nests of the Prothonotary
warblers. (Hoover & Reetz, 2006) This high level of brood parasitism can be directly
linked to forest fragmentation. My study will focus on surveying the songbird
communities in four distinct levels of succession and to determine how the songbird
community changes with habitat succession.
Habitat Fragmentation
Habitat fragmentation is the reduction or loss of habitat as it is subdivided into smaller
sections. This can occur due to natural causes such as hurricanes, fires, etc. but most
often it is the work of human actions. There are three major components to habitat
fragmentation: loss of the original habitat, reduction in habitat patch size, and an increase
in isolation of habitat patches. Biological diversity is reduced by all three of these
components. (Wilcox 1980, Wilcox and Murphy 1985). In landscapes that are highly
fragmented, the distribution or arrangement of the habitat patches is critical. The species
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diversity decreases exponentially as the distance between habitat patches increases when
only 10%-30% of the original landscape remains. The total area of habitat is of greater
importance to biological diversity than the position of the individual “islands” of habitat
when more than 30% of the original landscape remains. (Andren, 1994)
Whether a single large area of habitat or several small areas will protect more
biological species (SLOSS) addresses conservation of populations after habitat
fragmentation. (Wilcox & Murphy, 1985) Also important are the community interactions
between species at the time of the fragmentation. For example, one must consider how
the elimination of one species directly affects the survival of another.
Reforestation
The stages of succession and habitats as they change over time (Clements, 1916) have
been documented on landscapes across the planet. The directional change in vegetation
over ecological time can be predicted and monitored. Primary succession includes
landscapes with no biological legacy such as a newly formed island differs greatly from a
secondary succession landscape which has a biological legacy in the form of seeds, roots,
and some live plants such as Mt. St. Helens after its eruption. However, the restoration of
an entire watershed is a project at such a grand scale that it is quite rare. Reforestation of
bottomland forests in wetland areas can have positive impact to reduce nest predation and
brood parasitism. The concern is that more often than not, the management plans for
restoration projects are based more on speculation and less on true data from the
restoration site (Hoover & Robinson, 1999). Long-term restoration studies allow
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scientists to track biological populations over the lifetime of many species and document
their responses to the levels of succession (Hoover & Robinson, 1999).
Nest Predation
The number one cause of reproductive failure in birds is nest predation. (Nice, 1957,
Ricklefs, 1969, Martin, 1993.) In fragmented landscapes, the number of nest predations
increases and often allows the predators to come into contact with a larger number of
nests. In fact, in highly fragmented habitats, there may be very few nest sites safe from
predation. (Robinson, et al., 1995, Heske at al., 2001) The principal that disturbed
habitats are invaded more easily than pristine landscapes refer specifically to the richness
of the home species. (Simberloff, 1986)
In a fragmented bottomland forest, the three predators that are most effective hunters
are raccoons (Procyon lotor) snakes, and southern flying squirrels (Glaucomys volans) In
a study of 1156 nest predation events, raccoons were responsible for 73%, snakes were
responsible for15%, and southern flying squirrels were identified with 7% (Hoover,
2005). However, rates of nest predation decreased when the nests were over water
deeper than 60 cm. Primarily, it was the raccoons, the most prevalent predator, that were
reluctant to swim through the deep water to reach the nests. (Hoover, 2005) For birds
breeding in bottomland forests, the draining of wetlands can be detrimental to their
reproductive success.
Brood parasitism has a negative effect on the reproductive success of host birds. The
cuckoo (Cuculidae) in Europe and the Brown-headed cowbird (Molothrus ater) in North
America are two such avian parasites. The Brown-headed cowbird once followed huge
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bison herds across the Great Plains feasting on the available insects accompanying the
migration. Not having time to make a nest and incubate their own eggs, the cowbird
would fly into the edge of the nearest forest and deposit their eggs into the nest of a host
species. Today cowbirds continue to feed in pastures and row crops. Many shrubland
birds will eject cowbird eggs from their nest or abandon the nest altogether. The
Baltimore Oriole, American Robin, and Warbling Vireo are examples of these shrubland
species (Robinson & Herkert, 1997). In forests, however, the evolution of defense skills
has been much slower and 30-90% of migratory songbirds are parasitized.
Three arguments have been addressed by scientists to why the host bird accepts
parasitic eggs. They do not choose nest sites inaccessible to cowbirds, nor do they
defend their nests or desert nests that have been parasitized (Hoover, 2002).
Evolutionary lag or the short time of coexistence is one school of thought. (Hoover &
Robinson, 2007). The inability to recognize or reject parasitism is explained by
evolutionary equilibrium. A more recent discovery may include “mafia-like” behavior by
the cowbird to the nests of the host. In a study of 472 nest boxes, researchers discovered
that when they removed the cowbird eggs from the host nest, 56% of the time, the
cowbird would return and destroy the host eggs. Only 6% of the hosts that accepted the
parasitic eggs were depredated (Hoover & Robinson, 2007). This “mafia-like” behavior
has also been recorded in one species of cuckoo. This predatory behavior may slow the
evolution of rejection behaviors of the cowbird hosts that live in the bottomland forests
(Hoover, 2003). There are at least 100 species of cowbird hosts.
Prothonotary Warblers in the Cache River Wetlands
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The Prothonotary warbler (Protonotaria citrea) is a neo-tropical migratory songbird
that prefers to breed over water within forested wetlands. The Cache River Watershed
provides this unique habitat. The Prothonotary warbler is also an indicator of the
hydrological condition of the bottomland forest. Research implies that conservation
activities such as plugging lateral gullies, and natural processes such as beaver built
structures that hold water in forested areas contribute to the success of the reproductivity
of the warblers (Hoover, 2010). It has also been studied that the site fidelity of the
Prothonotary warbler is directly related to the rate of brood success (Hoover, 2003).
Over 80% of the double-brooded individuals, returned to the site in following years.
There is a relationship between the reproductive success and the decision to return to a
specific nesting site (Hoover & Hauber, 2007). Clutch size decreases with the number of
parasitic eggs in the nest. The success of both the warbler and the cowbird eggs
decreased for both, but were always higher for the cowbird nestlings (Hoover, 2002).
Nest predation is not affected whatsoever by the number of host or parasitic eggs in the
nest.
Study Description
The Cache River Wetlands include the Cypress Creek National Wildlife Refuge and the
Cache River State Natural Area in southern Illinois. This provides an outstanding
opportunity to study the relationship between the restoration of the bottomland forest and
the avian community. The natural processes that affect value and function of the bird
habitat can be evaluated. This study will include a bird survey in restored fields at
varying ages. The research will survey fields from corn fields (age 0 years) to early
successional grasslands (age 1-3 years) to shrubby/old field habitat (age 5-10 years) to
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young forest (age 11-15 years). Some plots would be next to bottomland forest; some
would not.
In particular, the study will be:

Documenting how the bird community changes with habitat succession

Documenting the songbird host community (those species present that could be
parasitized by cowbirds) in restored areas

Documenting whether any female cowbirds are detected by the surveys and if so
at what age of succession

Shedding light on how long it takes for bottomland forest restoration plots to start
functioning as forest habitat for breeding birds

Shedding light on how the restoration may reduce the severity of cowbird
parasitism for songbirds in nearby mature forests.
Additionally, the researcher will be learning to identify by sight and by song
approximately 20 of the main species that would be encountered.
Objectives
The objective is to determine how the communities of songbirds change with habitat
succession and to understand how the restoration of the fragmented forest may reduce the
severity of cowbird parasitism for songbirds nesting in nearby mature forest. It is
predicted that the survey of bird communities will show a relationship between the age of
forest succession and the species of bird present. An additional prediction is that the
severity of brood parasitism in the mature forest will be reduced by the restoration of the
bottomland. Therefore, if the severity of brood parasitism has been reduced by the
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restoration of the bottomland forest, then there will be fewer female Brown-headed
cowbirds detected by the survey.
Methods
Fields to be surveyed will be identified using ARC Maps and field tours
Figure 1. Sites Add’s Branch Corridor and Hickory Bottoms
Figure 2. Sites Main Tract, Porter Bottoms and Porter Bottoms East
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Figure 3. Sites Buttonland Swamp & Limekiln Slough
Figure 4. Sites Boss Island, Wildcat Bluff, Heron Pond 1 & 2
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Bird identification will utilize visual sightings as well as song recognition. The data
collected in each of the successional areas will be monitored on a daily basis for the
duration of the study. The data recorded will first compare the similarly aged
sample plots to each other and also compare younger restoration areas to older
restoration habitat.
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