Effects of various levels of predation and coverage on bird feeder foraging habits

A predator is an organism that consumes another organism. The prey is the living thing that the predator eats. These pairings include those between a lion and a zebra, a rabbit and a fox, or a bird and an owl (William et al. 23). Predator and prey typically coevolve together and have a significant role in each other's environments. The predator uses a variety of tactics to catch its prey, like increasing its speed, becoming sneaky, concealing while stalking the prey, and many others, because if it does not, it will perish. Likewise, the predator is an important part of the preys surrounding where the presence of the prey means danger and death can happen anytime (Gholamreza et al., 189). The prey therefore evolves the various mechanisms like speed, camouflage, having high since of smell and hearing, sharp sight, among others to evade the danger of the predator.

The natural covers with food, water, cover, and space are important for animals to survive in a cover. The amounts of these factors and their distribution have been associated with different influences on the types and distribution of wildlife found in certain areas (Adam et al., 15). It also determines the level of survival of the animals in the environment. Cover, for example, enables wild animals to make nests, escape from predators, seek shelter from cold, and to rest. Evergreen covers provide birds with nest sites during spring and cover them from thermal heat during winter. These differences in climatic changes determine the types of wildlife found in a specific area.

Characteristics of a cover determine its feeding habits, mating patterns, and adaptation to the environment. Most of the wildlife require largely underdeveloped covers for better survival and stay. Change in nature of covers has been associated with the type of species found in an area where they tend to change as the habitat changes (Georgia et al., 123). In some cases, the wildlife departments have been involved in changing the covers to suit the adaptation of specific wildlife to facilitate their survival.

Animals have been found to forage differently based on the amount risk of predation level available and the amount of ground covered in its cover. Places where the number of predators is high, research has found that the animals tend to avoid them for fear of being consumed by the predators (Pratas‐Santiago et al., 468). Different animals tend to show different foraging behaviors when the predator is around. Some of the animals would remain in the hideouts preferably in thick forests for fear of being attacked by the predators, but for the animals in areas of low coverage, the effectiveness of remain in hideouts is minimal. The animals likely to forage form areas with low coverage, they have adapted to high speed as a way to escape from the predator when danger looms.

Animals in areas of low coverage are better comfortable feeding in far areas away from the danger posed by the predator. The areas near the predators remain abandoned for fear of being consumed (Riofrío-Lazo et al., 267). The reliability of high speed is high for herbivores in covers invaded by fast running carnivores like leopard, lion, and cheetah. The herbivorous maintain huge crowds as a source of protection in case the predator attacks them. They also tend to remain under thick forests where they are not easily spotted and where there is a possibility of finding safer hideouts.

Optimally theory predicts that the hiding time is highly affected by emerging risk. Therefore, the risk time is decreased when the hiding time is increased (Weissburg et al., 145). Additionally, the cost of remaining in the hideout increases when the time of remaining in the hideout increases. Animals that stay in the hideout for long for fear of predation level are likely to die from starvation. They are therefore forced by the need to feed to come out of the hiding to get food. The areas with less risk of being preyed upon attract most of the harbors. Where the number of predators is very high, tend to be abandoned by the prey for fear of being fed upon (Chetri et al., 134). To determine the how predation level and ground cover (forested or open ground) affect how the animals (birds) feed, the following study was developed.

Methods and Materials

Hypothesis  

Null Hypothesis: Higher predation level and low coverage levels will not decrease foraging habits

Alternative Hypothesis: The presence of predators in low coverage will decrease foraging. The presence of predators in forest coverage will decrease foraging, but not as much as it appears in low coverage.

Experimental Design

The study was involved use of 18 bird feeders, 2 types of habitats (forested and open ground), and 6 plastic owls were used. 9 bird feeders were placed where 3 were placed near the owl (high predation), 3 placed 5metres from the owl (moderate predation), and 3 placed 20metres from the owl (low predation). The feeders were then filled with 200 grams of seeds and a card board placed below them to prevent rodents from feeding on the seeds.

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Data collection

The mass of seeds left in each bird feeder were measured two time in a day. The data collected and indicated as AM corresponded to the night time feeding habits while that of PM corresponded to the daytime feeding habits. After the measurements were taken by use of a scale, the feeders were refilled to 200 grams to for the nest feeding period. These took place continuously for a total of 10 days.

Data analysis

All the recordings were sorted into the various corresponding period of day either AM or PM. The data was also arranged as either having been collected from the forest of open area, whether the feeder was in a presence of low, moderate or high predation. By the use of Advanced excel analysis, a factorial ANOVA was run on all the independent variables (time, cover, predation level, time*cover, time*predation level, predation level*cover, time*predation level*cover) based on a single dependent variable, the mass of feed that was found to have been consumed by the birds. The 95 confidence intervals on all the independent variable were also run.

Results

From the findings in Table 1 below, it is evident that the predation level and cover are highly significant determining the feeding habits of birds from a bird feeder since their p-values are 0.000 and 0.049 respectively which are both less than 0.05. Also, the interactive effect of time and cover is highly significant since it has a p-value of 0.007 which is less than 0.05. The time factor is seen to be insignificant in determining the feeding habits of birds since it has a p-value of 0.541 which is greater than 0.05. Other insignificant independent variables are the interaction effect between time and predation level (p-value of 0.230 which is greater than 0.05), Predation level and Cover (p-value of 0.286 which is greater than 0.05); time, predation level and cover with a p-value of 0.252 which is greater than 0.05.

From Figure 1, the mass of feed removed during the night time (AM) was greater than that removed during the daytime (PM) although the results on time effect were not significant (p of 0.54089 > 0.05). As can be seen from figure 2, where the predation level is high, there is little feeding as compared to where the predation level is moderate to low with a high significance of (p-value 0.0000 <0.05).

From figure 3, it can be seen that forested areas had high feeding and compared to opened areas at a high significance level of 0.04877<0.05.

From figure 4, the findings on the effect of time and predation level are highly insignificant with a p-value of 0.22989 > 0.05, where the mixed effect of daytime effect on feeding have between witnessed across the three levels of predation level. The inconsistency of the results is evident.

Discussion

The results did not deviate a lot from the prediction. The greatest mean mass of seeds was fed upon where no predation level there was low predation level, followed by moderate predation level and lastly where there was high predation level. Moreover, the mean mass of seed removed was greater in the forest covers than in the open cover. Additionally, the mass of seed removed was greater in the PM than in the AM. Lastly, the only significant interaction effect was seen between time and cover (Time*Cover) upon the mass of seed removed. This suggests that their effects on foraging are not conclusive. However, an interactive effect for Cover*Predation level and Time*Cover*Predation level was not proven in the ANOVA. Nevertheless, as the P value of Cover*Predation level was below 0.05, it is likely that an interactive effect can be seen between these two independent variables on foraging if more trials were conducted. Contrary to the initial hypothesis, the effects of Time*Cover*Predation level are parallel, suggesting there is no interaction between all three variables. The lack of interaction can most likely be explained by the presence of a predator. Predation level would discourage foraging regardless of what time of day it is or what cover the prey is foraging in (Belgrad et al., 24). As predicted by optimal foraging theory, which aims to elucidate strategies that maximize resource intake, birds foraging will be the greatest in the least risky situations.

Birds are very likely to show non-lethal responses to predation level risk. Due to their large size, mobility, and behavioral sophistication, birds avoid predation level by movement or by reducing their profitability in high-risk predation level areas. These non-lethal effects are not limited to the functional response of the predator. For example, a small population of Peregrines can case a large population of Sandpipers to avoid an area even though the predators can only eat a small proportion of the available prey (Bueno‐Enciso et al. 1299). Although the per capita pre-mortality caused by predation level will decrease at high prey densities, non-lethal effects continue to increase with increasing predator numbers. In a sense, profitable predation level aversion tactics have led to the evolution of fearful behavior in gregarious animals. The consequence of this is that birds have lower diets in areas where predators are present; the risk of predation level outweighs the risk of starvation. Moreover, birds tend to regulate fat reserves and body minimizes starvation and predation level risk. Even though high body mass and fat percentages ensure against periods of food shortage, they carry risks of mass-dependent predation level (Winnie Jr et al., 104). As a result, birds will limit their body weight in areas with predators. This trend was seen in the data: the mean mass of seed removed was lower in feeders where an owl was present.

Changes in spatial and temporal patterns of abundance in birds have been shown to result from the avoidance of predators. For example, high dense forest areas are preferred for foraging, as mixed flocking, vigilance, and sentinel behavior serve to reduce predation level risk. The forest cover allots better cover from predators. The data supports this statement, as the mass of seed removed was greater in the forest than in the open environment. Birds, through predation level aversion tactics, prefer foraging in environments where they can easily flee and hide from a predator. Conversely, the very conspicuous positions of predator owl in the open environment served to discourage foraging in that area (Martínez‐Gutiérrez et al., 945). It is possible that because the owls were stationary, birds feeding in the open area could have realized that there is a lesser risk of being caught. However, the open environment makes birds susceptible to other predators as well. Through the development of this “ecology of fear,” or fearful behavior that prey will display to avoid predation level, birds simply minimize foraging in open, high-risk predation level areas (Creel et al., 775).

Vision is a vital sense in species, especially predators that search for food. Low light levels reduce the risk of predation level, by reducing the ability of predators to locate prey visually (Gerking & Shelby, 101). Thus with an increased risk of predation level, foraging and mass gain occur later in the day. In addition to the lower risk of predation level, the night provides an environment with greater food availability. Small prey in general move less during the night, causing many birds to hunt at night to supplement their diurnal diets (Lourenco et al., 2008). The mass of seed removed was greater in the PM than in the AM. This data validates the notion that birds forage more during the night, to lessen the risk of predation level as well as increase their daily food intake.

The birds in this experiment had to select their optimal level of vigilance, about their perceptions about the predator’s whereabouts. Additionally, they must establish a baseline level of apprehension that determines their level of vigilance in the absence of any evidence of a predator’s presence (Wikenros et al., 867). If the level of apprehension is set too high, the birds will miss valuable feeding opportunities. If set too low, the birds are likely to be killed by a predator. Thus by optimal foraging theory, and as supported by the data, birds chose to forage most during the night, in the forest environment, without a predator decoy present (Hayward et al., 258). The foraging pattern of these small birds can be designated to other animals as well. The fearful behavior of prey, when exposed to predators, is similar in any species; any animal will forage in the location where the risk of predation level is the least.

























References Cites

Belgrad, Benjamin A., and Blaine D. Griffen. "Predator-prey interactions mediated by prey personality and predator hunting mode." Proc. R. Soc. B. Vol. 283. No. 1828. The Royal Society, 2016.

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Chetri, Madhu, Morten Odden, and Per Wegge. "Snow leopard and Himalayan wolf: food habits and prey selection in the Central Himalayas, Nepal." PloS one 12.2 (2017): e0170549.

Creel, Scott, Paul Schuette, and David Christianson. "Effects of predation level risk on group size, vigilance, and foraging behavior in an African ungulate community." Behavioral Ecology 25.4 (2014): 773-784.

Gerking, Shelby D. Feeding ecology of fish. Elsevier, 2014.

Hayward, Matt W., Salvador Lyngdoh, and Bilal Habib. "Diet and prey preferences of dholes (Cuon alpinus): dietary competition within Asia's apex predator guild." Journal of Zoology 294.4 (2014): 255-266.

Martínez‐Gutiérrez, Patricia G., Francisco Palomares, and Néstor Fernández. "Predator identification methods in diet studies: uncertain assignment produces biased results?." Ecography 38.9 (2015): 922-929.

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Pratas‐Santiago, Luís P., et al. "Dodging the moon: The moon effect on activity allocation of prey in the presence of predators." Ethnology 123.6-7 (2017): 467-474.

Riofrío-Lazo, Marjorie, and Diego Páez-Rosas. "Feeding habits of introduced black rats, Rattus rattus, in nesting colonies of Galapagos Petrel on San Cristóbal Island, Galapagos." PloS one 10.5 (2015): e0127901.

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WARD‐FEAR, Georgia, et al. "Eliciting conditioned taste aversion in lizards: live toxic prey are more effective than scent and taste cues alone." Integrative Zoology 12.2 (2017): 112-120.

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Wikenros, Camilla, Sophie Ståhlberg, and Håkan Sand. "Feeding under high risk of intraguild predation level: vigilance patterns of two medium-sized generalist predators." Journal of Mammalogy 95.4 (2014): 862-870.

Winnie Jr, John, and Scott Creel. "The many effects of carnivores on their prey and their implications for trophic cascades, and ecosystem structure and function." Food Webs(2016).































Tables

Table 1: Factorial ANOVA results on the various independent variables.





















Figures

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