DOES BUILDING YOUR NEST ON A TREE BRANCH IMPROVE BREEDING SUCCESS? Tania Kalsi, Linda Lyu and Alexa Stutchbury (Year 9) Science Faculty, The Illawarra Grammar School, Western Avenue, Mangerton, 2500 Abstract Nest predation from other animals is a biotic factor that can have a major impact on bird populations, the study of nest predation can help scientists find out more about the bird species as well as the predators of nests. Two clay eggs were placed in nests made of halved tennis balls, coconut fibre and sphagnum moss, and then later were placed either in trees or on the ground to test which is at more risk to be preyed upon. These nests were observed and checked for disturbances over the next week and two days. 71% of the artificial eggs that were located in trees were disturbed by a possible predator, contrasted to the 50% of disturbed nests located on the ground. The reason behind this may be because nest predators have adapted to birds’ behaviour and tend to search for eggs on trees, rather than on the ground. This data would be useful for scientists in noting breeding behaviours of where birds commonly build their nests, as well as how the predators have adapted for survival. Introduction Nest predation from other animals is a biotic factor that can have a major impact on bird populations. Nest predation can be from many different species of animals, such as other birds, rats, possums, cats and lizards as eggs are a vulnerable and nutritious target. To protect their eggs from predation and increase breeding success, different birds have evolved different strategies, such as hiding the eggs in dense shrubs, building the nests on tall, open branches, or changing the colour of their eggs to avoid detection by predators, called “egg crypsis”. Nest predation is a key factor in the selection of birds that has attracted increasing attention from ornithologists. The study of nest predation can help scientists determine a bird species’ behaviour, population ecology, evolution and conservation biology.
In this practical activity, we will experiment to test if the second strategy (building nests on tree branches), will increase breeding success. We will build a bird nest, add plasticine eggs, position the nests outside, and check on the nests every lesson for signs of predation. Experiments like this one had been conducted since the 1980s, to find out more about the bird species as well as the predators of nests. Angelstam (1986) discovered in his studies that other birds were the most common predators of nests. Later in 1998, it was found out that nest predation in forests affects nests that are built above the ground more than nests that are on the ground, suggesting that nests built on trees are at more risk than nests on the ground. Hypothesis Despite the research done for the introduction, stating that nests built on trees are more likely to be disturbed, the original hypothesis is that nests positioned on the ground will be at more risk than nests positioned on trees, more nests on the ground will be disturbed. The reason is 19
