The Magpie Foraging and the Herbivory - Research Paper Example

The magpie foraging and the herbivory Table of contents The magpie foraging and the herbivory Table of contents 2 Vigilance in birds 3 Introduction3 Methods 3 Results 4 1.The correlation coefficient between the average number of birds in each flock observed and the average vigilance among birds in the same flock is -0.4, implying that the size of flocks indeed has a negative impact on the vigilance level among the birds. 4 2.Yes, the flocks are found to have a lower vigilance level as they fly to greater proximities. 4 Discussion 4 Patterns of herbivory on native and introduced plants 6 Introduction 6 Methods and Data Collection 6 Results 7 Discussion 7 Vigilance in birds Introduction The birds that forage or roost on the ground are prone to risk of predation. Their need to scan their surroundings before settling, reduce the amount of time that they can allocate to feeding, which is why they prefer to stay in flocks. This field exercise aims at investigating vigilance behaviour in ground foraging and ground roosting birds in nearby parkland areas. Methods First locate a group of birds on the ground and record the number of birds present in the flock along with the species. Scan the flock with binoculars and record the number of birds that have their heads up as well as the birds with their heads down or tucked under wings or feathers if roosting. Repeat the counts ten times at intervals of about 10 seconds, recording the number each time. Now move 10m closer to the birds (pace out the 10m) and repeat the 10 counts of vigilant birds recording the information, move closer again and continue to repeat the 10 scans for vigilant birds, noting whenever birds leave or join the flock. Continue to do this until the flock of birds takes flight. When they do that pace out the remaining distance to where the birds were and record this and also pace out the distance to where the majority of the flock resettled and record the average height of the birds when perched to the nearest meter. Continue the procedure until data have been collected on a range of flock sizes and species. Results 1. The correlation coefficient between the average number of birds in each flock observed and the average vigilance among birds in the same flock is -0.4, implying that the size of flocks indeed has a negative impact on the vigilance level among the birds. 2. Yes, the flocks are found to have a lower vigilance level as they fly to greater proximities. 3. Yes, the proportion of a flock that is vigilant at any one time increase when a possible disturbance (e.g. a person walking towards them) is advanced towards them. 4. Yes, different species have different ratios of vigilant to foraging birds. 5. Yes, different types of disturbance provide a different response. 6. Yes, the distance at which a flock takes flight differs depending on flock size or proximity to cover. 7. When the flocks disperse, they settle down in their nests. Discussion Analyzing the results, it could be concluded that among all the flocks of birds being considered, those for the Australian Wood Duck and the Crested Pigeon are found to be the largest of all. However, it is also noted that the larger the flock size gets, the lower is the average vigilance of the birds in the flock. The average vigilance level for the largest flock, i.e., the crested pigeon is found to be 33 percent, while that for the Australian Magpie, which stays in the smallest of flocks, is found to be as high as 81 percent. Another factor that is notable is that the flocks are found to get less vigilant as they travel more. On an average, i.e., taking all the flocks of birds together, it is found that the birds are most vigilant, viz., by 63 percent, when they are traversing a distance less than 5 meters that gradually decreases and finally are found to display just 23 percent vigilance when they are traveling a distance more than 40 meters. The main reason behind this could be that while the birds cover a smaller distance through walking, they usually fly when they need to travel longer distances. However, the distance that the birds travel by foot are prone to be more frequented by obstacles like, a person walking towards them, and this could be a very significant reason why they get more vigilant. However, it is also found that apart from the distance covered, the levels of vigilance among birds also are a function of the species that the bird belongs to. For example when the distance covered is below 5 meters, Noisy Miner, is found to display a vigilance of 92 percent compared to that of the Magpie Lark that exhibits a vigilance of just 50 percent even when the number of birds in each flock is found to be the same for both species. It is also found that the greater the flock size is, the lower is the tendency of the birds to take a flight. This is because the birds feel more secure when they roam about in larger flocks and that is why do not mind covering the distance through a walk rather than taking a flight that they usually do when they are more dubious about their surroundings and about their combined strength to protect themselves as well. Moreover, the birds are also found to prefer taking a flight when they have to cover greater distances since a flight can cover the same distance within a lower time span. When the flocks fly off, they are found to settle down on trees or their nests. Since the flocks mainly belong to the category which builds its nest on the ground, so they prefer to stay in a cohesive group in order to stay more protected and secure from the clutches of predators. Patterns of herbivory on native and introduced plants Introduction Plants evolve various morphological and chemical mechanisms for preventing herbivores from eating them. Herbivores, however, also evolve mechanisms by which they can counter the defenses of plants. This section of the practical involves documenting the patterns of herbivory found on the leaves of trees and using these data to infer something about past herbivory. For many plants herbivores are often inconspicuous but the damage they do to foliage is often conspicuous. We will document the distribution, abundance and types of damage found on samples of leaves and compare the rates and extent of damage between several individual trees of the same species and between several different species, particularly between Australian and non-Australian plants growing in nearby parklands. Methods and Data Collection First locate a number of individual trees belonging to the genus Eucalyptus that have low branches with foliage that could be examined on the plant. Select and grab hold of the branch at a point below which (out towards the tip of the branch) there will be about 100 leaves. Now systematically score the condition of each leaf from the point that you have selected and work towards the tip of the branch. For each leaf record the proportion of the leaf blade that has been damaged as 0%, < 10%, 10-30%. 30-70%, 70-90% and >90%. In addition for each leaf, record the numbers that has the edge of the leaf eaten; a central region that is necrotic or has been eaten, and record the number of any galls present. A suitable data sheet to record the data is attached. Try to score this information for three native trees (eucalypts) and three introduced trees. Results The level of damage (eg % leaves damaged) was not similar for all plants. Nearly 11% of the leaves of all plants on an average are damaged. The average level of damage for native trees is found to be a little above 14%, while that for newly introduced ones is about 9%, implying that the native trees are more damaged. Discussion Following the analysis from the results, it could be summarized that the plants on which the data are being collected, do not exhibit similar levels of damage as is prominent from the raw data collected on each plant belonging to two different types. From the summary data on each plant type, it is obvious as well that the percentage of plants damaged and not damaged also differ widely; rather the plants newly introduced are less damaged than those which are native. The number of damaged leaves of the plants newly introduced and those that are native are approximately 43 and 72 percentages of the total number of trees of each variety being considered. Thus the overall percentage of damage is higher for the native plants than those for the introduced lot. The reason behind this difference is that the introduced plants are basically non-Australian in nature and thus it seems that they had specially been planted which implies that the care under which they grow are much higher than those which are native to the land that often grow on their own. Besides emitting defensive chemicals, the plants also have other ways to protect it from the herbivores. One such way is the shapes that the leaves take. The thicker they get, it becomes more and more difficult for the animals to devour them and thus the latter ignore such category of plants. This is quite evident from the way the cactus leaves are shaped preventing animals from sustaining on them unless equipped with certain features. Read More