Catharus Bicknelli - Decline of a New Hampshire Bicknells Thrush Population - Assignment Example

Decline of a New Hampshire Bicknell’s Thrush Population, 1993-2003 Catharus bicknelli is a forest dwelling songbird, found at altitudes of 740m and above in New York, New Hampshire, Vermont and Maine, as well as in southeastern Canada. Its survival is threatened due to its restricted habitat, highly specific distribution and small surviving population (estimated maximum of 50,000). One third of potential C. bicknelli habitat lies in White Mountains. The preferred habitat of C. bicknelli is young or regenerating forests of Abies balsamea, Picea rubens and Betula papyrifera var. cordifolia. These alternative habitats of forests with recent history of fire or tree felling are characterized by dense vegetation and less than 6m canopy. In winters C. bicknelli migrates mainly to montane broadleaf forests of Dominican Republic. It has been listed as a priority species for most ornithological organisations of the locations where it is still surviving. This study aims to estimate the decline in the population of C. bicknelli during the period of 1993 to 2003. The area selected for the study was White Mountain National Forest in north central New Hampshire. Routes were charted to enable observation of maximum geographical area covered with coniferous forests and adjacent mixed forests, at elevations ranging from 740 to 1470m. Trained observers conducted annual point counts from June 5 to June 28, between 0500 and 1100 hrs EST; starting at one point and then using rope to station at point two, 250m apart. Observations were taken consistently in silent period of 5 minutes for 10 days every year, excluding days with rain or wind velocity above 40km/h. Annual trend of birds spotted or heard in all routes was fitted against time, for a common set of routes and points. The count in year y (Cy), was assumed to follow the following model: E(Cy)=A*by, where, b is the trend coefficient for the annual rate of change in population size. The model was fitted using non linear least squares, or in other words, Poisson regression allowing for over- or under-dispersion. The study revealed a substantial decline of the population of C. bicknelli during the study period; being maximum in small patches of Terrace Mountains and Mount Crawford while in expansive habitats of Carter Moriah Range and Presidential Range, least decline was estimated. Previous studies have revealed the eradication of C. bicknelli from several Island and coastal areas of Canada, Mount Greylock, Dixville Notch, NH and Brook Notch, ME. The population decline has also been reported from Massachusetts, New York, Vermont, New Hampshire and Maine. Cumulative data of observations of C. bicknelli from US as well as Canada are too scanty to enable deductions of any specific trends. Local disappearance of C. bicknelli might indicate a declining population; however this may also be due to a change in habitat. Site specific observations are also difficult to gather for C. bicknelli since it inhabits areas that have undergone disturbance in past and are regenerating, which in itself is a transient feature. It could be a possibility that the observed decline in population of C. bicknelli in White Mountain be due to a migration, which can be seen as an increase in population elsewhere, and the trend might reverse in post study period. In fact an increase has been reported by VCE (unpublished data), for the year 2005-2007 in New York and northern New England. However the same has been hypothesized to be improbable for three reasons: No increase seen in any of the routes in any survey during the entire span of 10years of study. The positive changes in population have been reported for a 3 to 6 year period, which is too short for a habitat location shift. High site fidelity of C. bicknelli. The major factors contributing to decline of C. bicknelli population are: 1. Winter Habitat Loss: The main wintering location of C. bicknelli, Dominican Republic, has undergone extensive deforestation. However further details of the use of existent winter habitats being unavailable no conclusive statement as to influence of this factor on population decline can be made. 2. Atmospheric Pollution: High incidents of acid rains in White Mountains, leading to leaching of Calcium from soils has been suspected to harm C. bicknelli. Since similar studies for other forest birds in Europe showed a decline in reproductive ability. Also accumulation of toxic methyl mercury in biological systems is a direct consequence of acid rain. Relevant studies are lacking for C. bicknelli. 3. Climate Change: Global warming has a negative impact on C. bicknelli population due to change in its habitat, leading to gradual replacement of Abies balsamea and Picea rubens with Betula alleghaniensis and Fagus grandifolia at lower elevations, thus restricting C. bicknelli to highest peaks. 4. Human interference: An increase of foot traffic in lower regions of White Mountain can be correlated with this factor too. To enable accurate estimates of C. bicknelli population, improvised research involving discrete route selection, sampling enabling tracking of location change, and better point counts methods are suggested. Finally, the conservation strategy of C. bicknelli should be intensified in the light of the declining population data. Effect of Forest Management On A Rare Habitat Specialist, The Bicknell’s Thrush (Catharus Bicknelli) The survival of forest dwelling birds is endangered by manipulation of forest ecosystems. Worst affected are the habitat specialists, e.g. Dendroica kirtlandii, thus resulting in a rapid fall in their population. Catharus bicknelli is a medium sized, rare bird with restricted habitat, found in northeastern United States and Canada. It migrates to Greater Antilles in winters and breeds in New York state, New England, Nova Scotia, Quebec and New Brunswick; in the dense coniferous forests and forests with trees regenerating post forest fires or tree felling. The home ranges of males are widely overlapping and both sexes have multiple mating partners the peak mating season being in June. A rapid decline in the population of the C. bricknelli demands an in depth study of the factors effecting its survival and breeding. Hence, research was conducted to study the effect of forest management practices, specifically during the various stages of a forest managed for silvicultural practices. The effect of forest stands as well as surrounding area on the habitat characteristics and abundance of C. bicknelli were studied. The location chosen for the study was Northumberland County of New Brunswick, which has an abundance of Abies balsamea, Betula papyrifera and Prunus pensylvanica. The study was done in June and July of the year 2003 and 2004. Stands in 5 different stages of a regenerating forest, were selected i.e. early stage or within 6-12 years after clear cut, prethinning stage or 11-13 years later, post-thinned stage or 13-14 years later, 2-5 years post-thinning and 14-17 years later; and finally, 7-12 years post thinning or 19-24 years later. Overall 29 stands were selected and surveyed 4 times during the 4th and 26th of June of 2003 and 2004, keeping the time (at dawn between 0425-0619ADT and at dusk 2050-2208ADT) and weather conditions (dry day, wind Read More