Overview

Introduction

Wildlife Studies

• Amphibians
• Birds
• Small Mammals
• Large Mammals

Possible Solutions

Literature Cited

Amphibians

Northern Leopard Frog (Rana pipiens), American Bullfrog (Bufo americanus)

Twenty percent of frog species in the Great lakes area are marked with special conservation status.  Therefore, it is imperative to research the cause of rapid decline of amphibians.  The dramatic loss in wetlands due to urbanization and the building of roads have isolated frog populations and created barriers to necessary movement.  Because subpopulations will be blocked from neighboring wetlands, the effectiveness of dispersal decreases; metapopulations (spatially separated populations of the same species) will not be able to re-establish their populations.

Birds

Ground Nesting Birds

Ovenbird Hermit Thrush

Over the past decade there have been numerous reports of a correlation between forest fragmentation and nest predation on songbirds in Minnesota. These studies suggest that small fragments of forests are becoming “sink” populations, because they are unsustainable and rely on “source” populations for survival. Forest fragmentation size may also play a role in nesting success, because the smaller the fragment the greater proportion of “edge” there is to its interior. However, even if a parcel of forest is considered a population source, such as forest-dominated areas this does not mean that it is completely unfragmented. Logging and development within these sectors still create a variety of edges and openings that can effect the local bird population. Manolis et al. (2002) studied the effect of clearcut edges on nesting success of ground-nesting birds in such a region. They found evidence of an edge effect near regenerating forests. 94% of nest failure was caused by predation and nesting success increased with distance away from the edge in ovenbirds and hermit thrushes. Nesting success was lower in the 0-100 and 101-500m from edge. Additionally, Ovenbirds within 0-500m from the forest edge appeared to be “sink” habitats, while birds further than 500m were in “source” habitats.

Their results suggest that certain ground-nesting songbirds are negatively affected from fragmentation in forest-dominated areas. Predator activity increases at edges of regenerating clearcuts and may enter the forest interior and increase predation. Therefore, continuous and large tracts of forest need to be protected to protect ground-nesting birds.

Additionally, Manolis et al. (2000) documented edge effects near clearcuts using artificial and natural ground nests in Northern Hardwood-Conifer Forest (NHCF) in Minnesota. Timber harvest in this area has dramatically increased in the last decade, leading to a number of open gaps and forest edges. They found that daily mortality rates for natural ground nests were greater near edges than in the forest interior. The artificial nest experiments suggested that predation rates were also greater at edges than in the interior. 75% of 177 nests 0-10m from clearcut edge and 46% of 174 nests 200m away from the edge were preyed upon. The results led to clear evidence of an edge effect in nesting success in an extensive forested area.

Robinson et al. (1995) found that forest fragmentation and cowbird parasitism correlates to ground nesting bird success. As previously stated, habitat fragmentation has led to a negative impact on populations of migrant birds. In addition fragmentation raises the rates of brood parasitism by brown-headed cowbirds. Cowbirds lay their eggs in other bird nests, which then raise cowbirds at their own expense. Cowbird populations are higher in fragmented landscapes, if habitats become more fragmented this care taking problem could lead to declines in migrant bird populations. The study focused on nine different landscapes within the Midwest region. They found that nest parasitism was negatively correlated to the amount of forest cover. Woodthrush nests with less than 55% forest cover were parasitized. Areas that were heavily forested had low levels of parasitism. Nest predation as well declined with increased forest cover. The ovenbird, hooded warbler, and indigo bunting had high daily predation rates in the most fragmented land. This study also gave significant evidence that “source-sink” population models could be applied due to predation and parasitism in fragmented landscapes.

All three studies supported and indicated that increased levels of fragmentation could lead to widespread population declines of several bird species. In conclusion, unfragmented regions need to be protected and large-scale restoration efforts to reduce edge effects are needed to reduce nest predation and parasitism.

Small Mammals

North Weastern Chipmunk (Tamias amoenus), Red Backed Vole (Clethrionomys gapperi)

Small mammals are important to forest ecosystems because they are a prey source for larger carnivores and a consumer of plants and invertebrates. However, high populations may be a poor indicator of habitat quality. Sulivan et al. (1999) researched the effect of clearcutting on small mammal abundance and species richness in British Columbia. The study found that deer mice, long-tailed vole, north-western chipmunk, and weasels were more abundant in clearcut sites than on forest sites. The mean species richness of small mammals was also higher on clearcut areas than on forest sites. Clearcut sites had four rodent species (long-tailed vole, meadow vole, chipmunk, jumping mouse, and weasel) that occurred only rarely in uncut forests. The southern red-backed vole was the only species found that had a higher mean abundance in forested areas than clearcut sites.

The research advocates that clearcuts supply diverse habitats for a variety of small mammal species. The results of the study also suggest that tracts of old growth forest and clearcuts of various ages should provide for sufficient abundance and diversity of small mammals in northern forests.

Meadow Vole(Microtus pennsylvanicus), Deer Mouse (Peromyscus sp.)

Another Canadian study by McDonald and St. Clair (2004), researched the effects of anthropogenic barriers, such as roads like the Trans-Canada Hwy (TCH), on the movement of small mammals, including meadow voles, deer mice, and red-backed voles. Barriers can impinge on animal movement between habitat patches and lead to isolated patches (habitat fragmentation), which significantly reduces immigration and emigration rates. The results show that small mammals were 20% less successful in crossing the TCH than in natural barriers (forest and prairie land). Generally deer mice were more success in crossing the road barrier than the other two rodents. The results show that road crossing only presents a moderate impediment to their movement. However, such moderate findings are unusual to past research. Certain factors may have had an affect on the overall study. Deer mice results may have skewed the data to a more neutral side because of their natural characteristics. Deer mice are nocturnal, therefore, less predation and traffic were occurring at the time of the study. The study also indicated that path complexity was highest inside the artificial barrier, may be caused by rodents quickly attempting to avoid traffic and predators. In summary, small mammals crossing the anthropogenic barrier had a moderately lower return success and more complex path structures compared to crossing natural barriers. Further studies are needed to fully understand the correlation between artificial and natural barriers on small mammal movement.

Even though the study sites were located in Canada the natural characteristics of both areas were similar to Northern Minnesota. Overall, these two studies suggest that small mammals are affected by habitat fragmentation in respect to clearcutting and artificial barriers. However, further research is needed to understand the impacts of these anthropogenic activities.

Large Mammals

Grizzly Bear (Ursus arctos)

Grizzly bear population numbers are so low they are considered threatened in the United States. Their habitat is also decreasing at alarming rates due to mining, timber harvest, and other resource extracting industries. For these reasons I focused my attention on this large carnivore, however, I was unable to find any research on grizzly bears in Minnesota. Nevertheless, I believe the findings from British Columbia and Montana can be applied to the bear population in Minnesota because of the similar habitat characteristics.

In order to calculate the response of grizzly bears to timber harvest, McLellan and Shackleton (1989), compared four radio collared bear’s location before, during, and after the extraction event occurred. They researched the amount of displacement from the bears to their natural habitats by dividing the habitat into three zones. The study showed that there was no significant difference in the bear’s use of designated zones. Only two out of the eleven were there differences in bear behavior due to industrial activity. Bears in close proximity (200m) to industrial activity in timbered habitats responded by avoidance and little displacement. It may be possible that bears are habituated to human activity and therefore show little or no response. Even though the bears showed no significant impact on human activities, further studies need to be conducted to measure the physiological effects on individual bears.

Cougar (Felis concolor)

Indicator species such as cougars can be analyzed to address the viability of a whole ecosystem, because they exist at low densities and require large areas. Beir (1993) studied several sites in California to determine the minimum amount of habitat and corridor size needed to maintain cougar populations. The statistical results showed that without immigration, extinction increases as area of habitat decreased. Additionally, a habitat area of 1000-2200km squared could support 15-20 cougars for 100 years; however, these minimum areas will no guarantee long-term survival. The study also indicated that if a wildlife corridor was available to immigrate three males and one female every ten years, an area of 600-1600 km squared would also be able to support a cougar population for 100 years. The research implies that with out available space and wildlife corridors cougar populations will eventually go extinct.

Moose (A. alces)

A 6.2 million-km network of public roads in the last four centuries have been placed on this land for human mobility. Ecological “road-effect zone,” the area that extends outward from road and has ecological effects on the surrounding ecosystem, needs to be determined.

Most moose migration occurs in the fall when young males disperse in search of available females. In Forman and Deblinger (2000) study on road-effect zones it indicated that moose populations do not avoid road areas due to noise or traffic. Fourteen moose were spotted crossing major highways in Massachusetts. They also tended to use human made objects as routes in fragmented land, such as railroads and power lines. It was suggested that moose might move through landscapes with no regard to human activity because of their low metabolic rate and hefty size.

Eastern Timber Wolf (Canis lupus lycaon)

In the late 19th century and early 20th century Eastern Timber wolf populations were extremely low due to logging, human settlement, and clear cutting. Because of this drastic decrease in habitat the wolves were forced into the northeastern corner of Minnesota (Fig.1). For this reason (low population numbers) the wolves went on the endangered species list. Now the population has been increasing steadily. In 1974 they have been listed as a threatened species instead.

Recent studies have found that timberwolves are moving into areas in northern Minnesota that were previously deemed uninhabitable because of close poximity to human activities. Wolves are considered one of the top predators in Minnesota, therefore, they are not limited to a specific ecosystem. Their distribution usually results in prey density, however, it has been found that areas with less human influences has more wolves then urbanized areas. Mladenoff et. al (1995) found that wolf pack territories are found more often in a mixed conifer-harwood forest and forested wetlands then in agricultural or lake areas. They also found that pack territories had a lower percentage of road density then nonpack areas, but neither contained more then 1.0 km/km2.

The study states that wolf populations are moving into Wisconsin and Michigan from Minnesota. But Wisconsin's highly fragmented land and road density could reverse current population trends. The fragmented areas may not give enough security to wolf packs like Minnesota and Michigan does. Therefore, it is imparative that Minnesota starts a long-term land management plan in relation to wolf populations so that Minnesota does not have the same problems as Wisconsin. Even though the study states that the timberwolf population in Minnesota is strong that does not mean that the growing population can be sustainable in decreasing forests.