DOES BUILDING YOUR NEST ON A TREE BRANCH IMPROVE BREEDING SUCCESS?

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

that higher positions are harder to reach for predators, as dogs and some lizards cannot climb trees.

Method

Artificial birds nests were made out of half a tennis ball, with coconut fibres and/or sphagnum moss glued onto the ball and a hole drilled in the middle to avoid them flooding with water. Two air dry clay eggs were shaped and placed into each nest. These nests were placed in foliage, with some in trees and others on the ground, high and low. The nests were observed for just over a week, checking for signs of disturbance every science lesson. When initially placed out, photos were taken of the position and condition of the eggs. If there were signs of disturbance, the affected nest was brought back to the classroom. At the end of the experiment, each student in the class returned their nest to the classroom, the results and locations of their nests were placed in an excel worksheet for further analysis.

Results

Total number of nests 22

High position disturbances 10/14 (71%)

Low position disturbances 4/8 (50%)

Discussion

Predators in the neighbourhood predate the egg by leaving a mark relative to the animals’ mouth shape. This includes birds, which leave triangle marks on the eggs, where the larger the bird, the larger the triangle. Rats, mice and possums leave their teeth marked with 2 teeth at the top and 2 at the bottom, as well as frequently chewing eggs until they crumble. Moreover, lizards leave many small dots on the eggs arranged in a circular shape.

Birds in the location of the experiment include lyrebirds, cockatoos, kookaburras and tawny frogmouths. The lyrebirds’ eggs are black with small dark dots to camouflage them with dirt and the dark to protect their eggs from predation. The cockatoos’, kookaburras’ and tawny frogmouths’ eggs, however, are pale because they instead have evolved to camouflage them with their large feathers. To further increase breeding success, these birds from nests to ensure the safe development of their young. They often locate their nests in dense, hidden shrubs to prevent predation, but some larger birds build them in open areas as they are more competent in protecting their eggs. Some birds thus do not even form nests at all and instead simply lay their eggs on the ground, such as Emperor Penguins.

During breeding, the parents usually take turns incubating (i.e. the process of sitting on eggs to sustain their warmth before hatching) their eggs to maintain an ideal temperature for the normal development of their young. For kookaburras, however, the presence of additional male helpers and female helpers during incubation neutrally and negatively impacts the nesting success respectively. They typically have a longer length of incubation, as the larger the bird, the longer the incubation period.

As the results convey, 71% of the artificial eggs which were located in trees were disturbed by a possible predator, contrasted to the 50% that was located on the ground. The trees thus appear to be the usual site for birds to build their nests, as the high level isolates their young from common ground-level

20

predators such as possums and dogs. Therefore, high-level predators, such as magpies and ravens, have adapted to their environment and are aware that other birds often lay their eggs in trees, so they aim to predate up high. Some predators, such as snakes and rats, have also adapted to birds’ behaviour and are accustomed to preying for eggs in trees. Having said that, a considerable number of eggs were predated on the ground, as nests can generally be found almost anywhere and there are numerous groundlevel predators.

This data would be useful for scientists for noting the behaviours of birds when breeding in relation to where they commonly build their nests, as well as where predators often search for nests based on the egg disturbance. However, this experiment only used pale eggs, which are the easiest colour for predators to spot, thus the results obtained would be overestimated for another colour of eggs. The placement of each egg (i.e. if eggs also were placed in open, well-camouflaged or dense areas of the bush) was also dismissed, which greatly affects the likelihood of predation as explained above, thus significantly impacting the acquired data.

References

Birds In and Around Wollongong | Destination Wollongong 2020, Destination Wollongong, viewed 7 December 2021, <https://www.visitwollongong.com.au/birdsin-and-around-wollongong/>. Brakefield, PM 2009, ‘Crypsis’, Encyclopedia of Insects, pp. 236–239, viewed 7 December 2021, <https://www.sciencedirect.com/topics/agricu ltural-and-biological-sciences/crypsis>. Celis, P, Graves, JA & Gil, D 2021, ‘Reproductive Strategies Change With Time in a Newly Founded Colony of Spotless Starlings (Sturnus unicolor)’, Frontiers in Ecology and Evolution, vol. 9, viewed 7 December 2021, <https://www.frontiersin.org/articles/10.3389/ fevo.2021.658729/full>. Clarke, M 2019, Birds, nests and tree hollows, The Maitland Mercury, viewed 7 December 2021, <https://www.maitlandmercury.com.au/story/ 6328111/birds-nests-and-tree-hollows/>. Ibáñez-Álamo, JD, Magrath, RD, Oteyza, JC, Chalfoun, AD, Haff, TM, Schmidt, KA, Thomson, RL & Martin, TE 2015, ‘Nest predation research: recent findings and future perspectives’, Journal of Ornithology, vol. 156, no. S1, pp. 247–262, viewed 7 December 2021, <https://link.springer.com/article/10.1007/s10 336-015-1207-4>. LibGuides: Laughing Kookaburra (Dacelo novaeguineae) Fact Sheet: Reproduction & Development 2021, Libguides.com, viewed 7 December 2021, <https://ielc.libguides.com/sdzg/factsheets/lau ghingkookaburra/reproduction>. NestWatch n.d., GENERAL BIRD & NEST INFO, Cornell University, New York, viewed 8 December 2021, <https://nestwatch.org/learn/general-birdnest-info/nesting-cycle/>.

21

THE EFFECT OF NEST HEIGHT ON BREEDING SUCCESS

Chi Hin Elvis Suen (Year 9) Science Faculty, The Illawarra Grammar School, Western Avenue, Mangerton, 2500

Abstract

Bird nests, one of the easiest targets, have been prayed by many different predators, for instance, birds, lizards, rats etc. Since bird nests are easy to become targets, in this experiment, a fake birds nest would be made of half a tennis ball, modified by coconut fibre and shaped around the nest. After that, two counterfeit eggs made of clay will be put into the bird nests. There are 23 made, and half of them would be placed on the ground, and another half would be placed on the tree around 1.6 m from the ground. This would test the hypothesis that there are differences between putting the nest on the ground and on the tree. According to data, the study suggests that the higher the nests located, the more difficult to breed successfully.

Introduction

These are a few studies that have been conducted to explore the relationship between the height of the nest with breeding success. According to the study; The effect of nest height on the seasonal pattern of breeding success in blackbirds. This study has found out that height is critical for breeding. Height over 3m has the most success percentage compared to the other two types of nests put lower. Furthermore, according to the study, Seasonal increase of nest height of the Silver-throated Tit (Aegithalos glaucogularis): can it reduce predation risk? This investigation suggests that putting the nest lower will increase the rate of breeding success. However, refer to the study, The effect of nest height on the seasonal pattern of breeding success in blackbirds suggests an opposite result. This study completed by Ludvig et al. indicates that the breeding success will increase when the nest is put higher. In this study, nest predation is examined according to the height of the nest, and predators will be identified. This investigation hypothesises that the higher the nest are, the higher breeding success will be.

Method

Each student would make a nest with half a tennis ball and fibre to create the nest as natural as possible. Moreover, two eggs would be made with clay. When students have a science lesson, observation would be done and recorded. According to different observations, different actions would be done; when an animal attacks the nest, the nest would be taken back to the lab for a closer look. If animals did not attack the nest, the nest would not be moved or touched. The result will be collected after a week, and the result table will construct.

Results

In this experiment, the data showed that nests that had been disturbed were significantly greater than nests that had not been disturbed. However, nests that have been disturbed were concentrated in a high place; around 71 % of disturbed nests were located on trees and ground only have around 29%. According to the data, there was no effect on breeding success in low positions, by compare using diagram, the numbers of disturbed and disturbed had no difference. These numbers suggested that putting the nest in high places would increase the chance of being disturbed and

22

diminish breeding success.

Position of nest

High Low Total

Disturbed 10 4 14

Not disturbed 4

Total 14 4

8 8

23

Discussion

The result was opposite to the hypothesis and the study “The effect of nest height on the seasonal pattern of breeding success in blackbirds” but agree with the study “Seasonal increase of nest height of the Silver-throated Tit (Aegithalos glaucogularis): can it reduce predation risk?” In the experiment environment, predators like birds, rat and lizards are around as neighbours since the environment is more likely to be their habitat while doing the experiment. The data have shown there were more nests located at high places being disturbed; this is more likely because the number of birds that live around the area is many, which cause an increase in the chance of being disturbed. On the other hand, the result might have shown that birds could discover nests located in high places than low places even on the ground; however, these birds' behaviour has not been investigated in the experiment.

Even though the result suggests the nests being set on the tree have a higher chance of being disturbed, those birds who choose to locate their nests on the tree are related to their size. According to the article, “growing Illawarra natives”, this website showed 13 types of bird that put their nests on ground and most of their sizes are big. This suggests that when birds are large, they are keen to set their nests on the ground. In Wollongong, the most of the

23

birds are small and trees are able to take their weight. Therefore, the research shows that the height of the nests might have a relationship between, but further research and experiment should be complete before make the judgement. If the idea was correct, that might explain the reason there were more nests being disturbed on the tree. Since there are more birds that are small, according to the ideas, more birds will keen to look for bird nests from the tree. However, this was a though and should be seen as correct after investigation. This result might be helpful for this type of experiment because this provided an example that helped their predation become better, moreover, suggest there were more investigation should be complete before the understanding of birds is clear.

The disadvantage of this experiment female birds was not in the nest to guide and protect the eggs. Further investigation and research may set a fake bird to protect the eggs. In addition, even predators will leave marks for identification but setting a camera to recognise the specific predators can provide detail about that predator

References

Guan, H., Wen, Y., Wang, P. et al. Seasonal increase of nest height of the Silver-throated Tit (Aegithalos glaucogularis): can it reduce predation risk?. Avian Res 9, 42 (2018). https://doi.org/10.1186/s40657-018-01354 LUDVIG, e., 2021. [online] Avibirds.com. Available at: <https://avibirds.com/wpcontent/uploads/pdf/merel3.pdf> [Accessed 7 December 2021]. Bird Feeder Hub. 2021. 13 Examples of Ground Nesting Birds (With Pictures) - Bird Feeder Hub. [online] Available at: <https://birdfeederhub.com/groundnesting-birds/> [Accessed 7 December 2021]. Growing Illawarra Natives. 2021. Illawarra birds. [online] Available at: <http://blog.growingillawarranatives.org/p /local-native-birds.html> [Accessed 7 December 2021].

24