ABUNDANCE AND DIVERSITY OF BIRDS ON THE FORESHORE AT BOGGLE HOLE

Introduction

                During low tide, the rocky foreshore of Boggle Hole and Robin Hood’s Day exposes excellent feeding habitat for many species of wading and coastal species of birds. The exposed rocks are covered in gastropods, limpets, crab and many aquatic plants for the birds to feed on. The cliff faces and shore is also a good breeding habitat for some species, such as the Rock Pipit (Gooders 1995), however not many bird species breed over the winter months due to the harsh weather conditions. This is a study into the diversity and abundance of the birds on the foreshore of Boggle Hole in one day in October. 

              There are two working hypotheses that will be tested. The first is that if there is more foreshore available, there will be a greater abundance and diversity of birds. This will determine whether tide has an effect on the abundance of species. The second working hypothesis is that if more foreshore is available further down the beach at low tide, there will be a higher abundance and diversity of birds there.

Methods

                Observations were carried out at five minute intervals at six 150m intervals (see figure 1) down the beach in the morning, when the tide was going out, and in the afternoon, when the tide was coming back in. The species observed landing at each section of beach was recorded in 5 minute intervals, with 5 minute gaps between each observation period.

                After the observation periods, all the data was gathered together. The total number of individuals (irrespective of species) per 5 minute observation period was calculated, then average counts for the total period and each species observed during the 2 hour session. A Shannon diversity index was calculated for each 5 minute period.

                The test whether tide has an effect on abundance or Shannon diversity of birds, Mann-Whitney U Tests were done.

                To test whether observer location down the beach has an effect on abundance or Shannon diversity, Kruskal-Wallis tests were carried out.

Results

Figure 1 shows the mean numbers of birds seen along the beach. 

Figure 1 – Mean and standard deviation for numbers of birds observed on the foreshore of Boggle Hole in the morning and afternoon.

From the graph shows the mean and standard deviation, it appears that positions 6 and 7 were much more abundant with birds, and much more so in the morning when the tide was going out. There seems to be not much variance in the afternoon results, when the tide was coming in.

Figure 3 shows the Shannon diversity of the birds along the beach

Figure 3 - The average Shannon Diversity for each position along the foreshore of Boggle Hole

                Figure 3 shows the Shannon Diversity of the birds found at Boggle Hole. From this graph it appears that further down the beach there is a slightly higher diversity of species and higher diversity of species in the afternoon, but there is not a great difference from the morning.

Table 1 shows the results of the statistical tests carried out on the data.

Kruskal-Wallis Test	MEAN	SHANNON DIVSERITY	SIGNIFICANCE
X² Value	8.665	9.649	None
P Value	0.123	0.086	None
Mann-Whitney U Test
P value	0.936	0.575	None

Table 1 – Results of statistical tests

The Kruskal-Wallis test results in table 1 show there is no significance between observer location and abundance or Shannon Diversity of birds on the foreshore. The same can be said for the Mann-Whitney U Test results for whether tide has an effect on abundance and diversity.  Therefore we can accept the null hypothesis that observer location and tide direction have no affect on bird abundance and diversity for both instances and reject both of the working hypotheses stated in the introduction.

Discussion

                Both working hypotheses were rejected, so therefore tide and position along the foreshore of boggle hole have no affect on the abundance and diversity of birds found there. It also means that if there is more foreshore available the birds are just as abundant as they would be with little foreshore.

Many factors could have affected the abundance of birds on the day the observations were carried out. These include the weather on the day. If the weather was very bad out to sea, more animals may have come to the shore to feed and the sea would have been too dangerous for them. The weather on the foreshore may also have had an effect. If the wind was too strong, for example, the birds may have flown further inland where the weather was not as strong. The time of year could also have had an effect on results. As it was the beginning of winter, many species have flown south for the winter towards the warmer climates.

Only a very limited sample was collected from one portion of the beach over a relatively short period of time in one day. If the time was extended to a period of a week or so, a lot more data would have been collected. The same can be said if we used a longer section of beach. We could also have recorded the high and low tide times during the day, as we would then have a more accurate account of when the tide was going out and coming back in.

We could also have tested to see whether there was an increase or decrease of certain species during the day. This would have given us a more accurate result on total abundance of birds. One species in the morning may have been replaced by another in the afternoon. There may have been quite a few species, but half of them replaced by the other half in the afternoon, therefore there would have been an abundance reading of half that what was actually seen.

It is also possible that the same bird could have been recorded many times, in the same position or at different positions down the beach. So this would mean birds appeared to be more abundant when in fact it was just the same bird many times.

Reference

Gooders, J. 1995. Pocket Guide Birds of Britain And Ireland.