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During the initial data collection efforts at Surrey Bend Regional Park, there were no difficulties in implementing my sampling strategy. However, after consultation with the professor we decided that the habitats being examined were not similar enough to compare, and that the anthropogenic influences on them were too different to be able to effectively account for any changes in bird species presence and abundance to only one explanatory variable. As a result, I have decided to change the location of my research project to Burnaby Lake Regional Park and the surrounding area, and focus the study on examining bird species presence and abundance at three sites along an urbanized gradient.
My revised hypothesis is: Bird species presence and abundance is impacted by the percent cover of natural habitat at a site.
My revised predications are:
- Bird species richness will be highest in areas with the highest percent cover of natural habitat.
- Bird species abundance will be highest in areas with the highest percent cover of natural habitat.
My response variable will remain as bird species presence and abundance (continuous variable), and my explanatory variable of percent cover (categorical variable) of natural habitat (forest, wetland, etc…) vs. anthropogenic habitat (roads, buildings, trails) at each site as a whole will also remain the same.
In addition the followings changes will be made in the experimental design in regards to the way data is collected:
- Initial sampling took place mid-day and overall detectability was low. It is standard bird inventory procedure to sample only between dawn and 10:00am to increase detectability. I will now perform all my surveys during this period to maximize the birds being detected by sight and song.
- My new sampling strategy includes two survey sites (point count surveys) in each of the three habitats along the gradient. During the replicate exercise, I expanded the number of point count surveys in one of the sites to five. While it would be ideal to maintain this type of replication it is too time consuming to perform five replicate surveys in each of the three sites. As a result, I will perform two replicates per site, and will conduct surveys at each site on at least three different days.
During the next blog I will go into more detail on the sampling strategy, sample unit, how these changes have impacted the data collection, and any ancillary patterns that appear in the data to support the new hypothesis and predictions.
Hi Brian,
It sounds like you have a very well thought out study and that you have adapted your study design and sampling methods appropriately for the field conditions that you encountered.
I noticed that your hypotheses refer to bird species richness and abundance in relation to percent cover of natural habitat. You then mention that the percent cover is a categorical value. As percent cover is on a continuous scale, have you considered looking at this as a continuous variable as well? I would be curious to know if that would show different results or trends.
Also, will you be differentiating between the different types of natural habitat? You may want to consider limiting your study sites to areas having similar natural habitats as much as possible, as there can be enormous variation between say, a young regenerating forest with little understorey vegetation and a wetland, for instance.
Good luck!
-Kersti