Handling Time Behaviours In Poecile Atricapillus Biology Essay

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Animals foraging behaviour involves a series of unconscious decisions which have a perceived cost and benefit. Animal foraging behaviour seeks to maximize the benefit and minimize the cost which results in the most optimal foraging strategy available to the individual. We chose to design an experiment to test certain foraging strategies in Poecile atricapillus, more commonly known as the black-capped chickadee. More specifically we tested two specific foraging strategies, distance to food patch, and handling time at patch using covered and uncovered feeders at different distances to cover. Chickadees forage for food often and have easily observable strategies and thus made good test subjects for this experiment. We predicted that chickadees will favour the the uncovered feeder near cover and the least selected feeder would be the covered feeder far from cover. We used two statistical analyses to determine the significance of our results. In each of our test treatments as well as the interaction between distance to patch and handling time we found very small probabilities that our results were due to chance and a that our results were actually highly significant. Our hypothesis was supported by our results and we were able to conclude that chickadees perceive distance to patch to be a more important factor than handling time when deciding to forage for a food source. We also found that the most optimal foraging strategy for chickadees was the shortest distance to patch with the shortest perceived handling time. Finally we found that an increase in distance to patch and an increase in handling time negatively correlate to chickadee foraging behaviour.

Introduction

Foraging for food is something most animals have to do everyday. This involves certain behavioural decisions on where to get food from and how to get it. Animals have to decide how long they should forage in a certain area before moving to another spot. They also have to decide on the costs and benefits as to which kinds of food to choose and which to leave behind. Even more choices face animals such as how much time they should spend searching for food rather than doing other activities such as mating or resting. These are daily decisions animals make and there are certain ecological factors which affect their decisions such as the ability to survive. Animals don't make decisions in the same conscious ways that we do. Instead they have to weigh the costs and benefits of their behaviours and make changes depending on environmental changes or conditions such as weather or presence of predators. Even though behavioural decisions are measured on a scale of lifetime reproductive successes or fitness, we can measure the cost and benefits in other important ways such as rate of food intake. When faced with behavioural options, animals usually choose the strategy that is most likely to have a positive impact on their survival or reproductive success (Cuthill & Houston 1997). Optimal foraging theory aims to explain an animals diet-choice behavior from the evolutionary theory standpoint (Berec et al. 2003). There are specific models that are created to mimic certain environmental and behavioural scenarios animals are faced with such as handling time models (Berec et al. 2003)

Black-capped chickadees are small birds with easily observable foraging strategies. When feeding at a feeder, chickadees make brief visits and usually leave with one seed at a time in their bill. They then fly away with it to a nearby perch or tree to eat or store it (Smith 1991). Since chickadees typically fly off with one seed at a time, the number of feeder visits is a good indicator of the number of seeds taken. Although bird feeders allow chickadees to have a readily available food source, their decision to visit a feeder can subject them to predation by other animals such as cats and predatory birds (Dunn & Tessaglia, 1994). Because of this chickadees are more likely to choose feeders close to cover. Feeders close to cover also are preferential because chickadees like to eat seed or store seed in trees (Smith 1991). Feeders that are closer to cover allow the chickadee to spend less time and energy to get to the feeder versus farther ones. It is important to test these behaviours in order to gain a better understanding as to why animals make the decisions they do. In this experiment we chose to measure the benefit of foraging versus predation risk (cost) using two dependent variables. We designed an experiment to see whether chickadees preferred to forage at feeders close to cover or at ones farther away (travel time to patch) as well as whether chickadees would forage more at a feeder that was covered versus uncovered (handling time). Essentially we will measure the preference of a covered feeder versus distance to cover by measuring the number of chickadee visits. I predict that chickadees will choose seeds from the uncovered feeder close to cover the most. Conversely, I think that chickadees will choose seed from the covered feeder far from cover the least.

Materials and Methods

We chose two different test sites along Saskatchewan Drive at the University of Alberta, named zone 1 and 2 respectively. We chose two sites not only to obtain more data, but also to eliminate more confounding variables such as randomly choosing a site that has a predatory bird nest nearby. Two 0.9m sharpened wood stakes were used to make 4 holes where we placed four 1.5m long sharpened wooden stakes. A bucket of water was available for use to help soften the ground to more easily make the holes. Two stakes were placed close to the wooded vegetation (NEAR feeders were 1.5 feet away from cover) and two farther away (FAR feeders were placed 10 feet from the near feeders) to test distance food patch behaviour. The two feeders that were placed at the same distance from cover were 6 feet apart from one another. We set these distances so that it would be more obvious that the chickadee needed to make a choice, and yet close enough that the chickadee could see all available options. Two 0.3m lengths of 2X4 boards were used to pound the stakes into the holes. A 0.3m square plywood platform was placed on each stake and each was secured with 7.5cm nails using a hammer. Then one metal pie plate was placed on each platform and secured with a nail. A 25kg bag of unsalted sunflower seeds with shells was used to fill up each pie plate. A second pie plate with 6 holes cut in it was placed on top of one of the NEAR feeders and one of the FAR feeders as the handling time treatment. This whole procedure was repeated in zone 2. We observed the chickadee feeding behaviour over 10 days, from Thursday October 13 to Sunday October 24. We observed each zone for 15 minutes at a time, from 8 am to 10:30am, choosing the morning as it is an optimal foraging time for chickadees. Each time a chickadee visited a feeder we recorded it as one seed being taken. We also noted any other noticeable details such as the presence of other animals, eg. Magpies, as these could affect chickadee foraging strategy. All of the results were compiled in an excel spreadsheet. We used two statistical analyses to determine the significance of our results. The first was a two-factor ANOVA test with replication because we have two independent variables and are comparing more than two means to find the statistical validity of our results. The anova test reduces type one error. The second is a regression test to determine how chickadee feeding is affected by our two treatments, and the values allow us to predict values of an increased effect. P-values were calculated to determine whether we could reject the null hypothesis, that the results are due to chance alone, in favour of our test hypotheses.

Results

The most visits were recorded at the near, uncovered feeder (A) than any other feeder with a total of 665 chickadees counted (see Table 1). The far and covered feeder (C) received the least amount of chickadee visits with only 82.01 instances being counted (see Table 1). Since both of the near feeders received many more visits than the far feeders, it appears as though chickadees prefer less travel time to patch (total near = 865, total far =178.01). Therefore, 83% of chickadees preferred near from far feeders. Conversely, when comparing preference for the covered or uncovered feeders, chickadees preferred uncovered feeders (total covered=282.01, total uncovered=761). Therefore, 73% of chickadees preferred uncovered over covered feeders. By looking at the percentage of preference for each treatment alone, 10% more chickadees choose a distance to patch strategy when foraging for food over handling time. When looking at the average number of chickadee visits per 15 minutes, the near-uncovered feeder (A) had the highest result (avg=7.732, see Table 1). The feeder with the least average number of seeds taken in a 15 minute time period was feeder C, the far-covered treatment (avg=0.953, see Table 1). Looking at graph 1, we can determine that there is interaction between the two independent variables because the slopes of the two lines are not parallel. Since there is a difference in heights between the average points of each line, we can determine that there is an effect of the metal cover (covered or uncovered treatment). Since there is a difference between the two averages of the endpoints of each line on this graph, we can conclude that foraging is affected by distance to cover. We used the two-way Anova statistical test with replication and we found that the population means for the distance treatment are not equal (d.f.= 1, F=58.57412, p=2.04x10-13, see Table 2). The population means for the metal cover treatments are also not equal (d.f.=1, F=28.47461, p=1.74x10-7, see Table 2). From the Anova test we also found that there is a significant interaction between distance to cover and the metal cover treatment (d.f.=1, F=25.24511, p=8.17x10-7, see Table 2). Therefore, the main effects are both significant, as well as the interaction between the two treatments. Since all of our p-values were very small and less than 0.05, we can reject our null hypothesis that our results were not due to chance alone and are instead very significant (see Table 2). In our regression test, we can again reject the null hypothesis and determine that there is a significant linear correlation between distance to cover and metal cover treatments (Fsig=9.9x10-11, t-stat=3.781229, intercept p=0.00216, see Table 3). We can also deduce from this test a negative correlation, that the farther away the feeders, the less chickadee visits would be received and also less holes in the covered feeder (more covered), would result in less chickadee visits.

Discussion

Since the population means for both the metal cover treatment and the distance to cover treatment were not equal, we can deduce that there is a significant effect of each of these factors on chickadee foraging behavior. Since we were able to reject the null hypothesis in both of our treatments as well as the interaction between our two treatments, we have statistically significant support for the two test hypotheses. Chickadees prefer to forage at feeders closer to cover with less handling time involved. There is a negative correlation for the increase of each treatment, increase in travel time and increase in handling time result in less chickadee foraging. When foraging, chickadees prefer a shorter distance to a food patch then a longer one. They also prefer less handling time. Dunn & Hussel (1991) performed a similar experiment, however they tested height and distance from cover. They found significant results with height of feeders but found no difference between distance from cover in the low feeders. Elchuk & Wiebe (2002) found that foraging behaviour in birds is influenced by time and energy spent searching for and handling food, as well as the energetic value of the food. Lee et al. (2005) found similar results in that feeding efficiency was lower at open sites than edges sites, except when predation risk was high. Distance to food patch is a more important factor than handling time in chickadee foraging strategy. It's possible this is due to a greater perceived cost to chickadees in traveling farther to a patch when obtaining food is uncertain. This is consistent with the findings by Walther & Gosler (2000) where a safety-first strategy precluded visits to abundance of food patches if they were too far from cover. In two other similar experiments, they found that sparrows foraged at feeders closer to tree cover when given a choice and shifted to farther feeders as food become more scarce at the feeder near the tree cover (Schneider 1984; Giesbrecht & Ankney 1998). A closer patch, with less handling time proposes the most benefit and least cost to the chickadee. Of all four options, this is the most optimum foraging strategy. The strategy, chickadees associated with the most cost and least benefit was the far-covered feeder. The costs to the chickadee, which they seek to minimize are things such as predation risk and energy expended.

There are a few limitations that we must take into account when considering the results of our experiment. The first is the presence of other animals present at the time of data collection. On a few of the days, there was a red squirrel running around the feeders deterring chickadees from feeding. When predation risk increases, time for foraging decreases (Suhonen 1993). Also the type of cover nearby could have an effect since we used two different sites. Suhonen (1993) found a slight difference between foraging behaviours near thicker more protective species of trees. The close proximity of the feeders to the street and sidewalk would have had an effect on chickadee foraging as well. Some mornings were particularly busy and noisy from nearby construction. Juricic (2000) found that pedestrian rate negatively affected probabilities of patch occupation. A few of the days there was snowfall which would have affected our results as well. Although we tried to do all of our data collection within certain time parameters, there was one day in which data collection took place an hour earlier (7am) and this could have affected our results. And finally there were other chickadee feeders nearby especially to zone 1 which would have affected chickadee choice to feed at our feeders versus the other ones from another experiment. In the future it would be interesting to test height of the feeders to the ground and see the effect on chickadee foraging behaviour. Also further study should determine whether other habitat features influenced results. As well as further studies conducted on other species would be valuable.

Foraging cost compromise the energetic cost of metabolism, cost of harvesting, predation risk and missed opportunity cost (Hughes & Ward 1993). Prey species may alter their behaviour in response to varying levels of risk, since this has important implications for behavioural, evolutionary, and community ecology (Morrison et al. 2004).

Literature Cited

Berec, M., Krivan, V., & Berec, L. 2003. Are great tits (Parus major) really optimal

foragers? 780-788

Cuthill, I. C. & Houston, A. I. 1997. Managing time and energy. In: Behavioural Ecology: An Evolutionary Approach. 4th edn. (Ed. by. J. R. Krebs & N. B. Davies), pp. 97-120. Oxford: Blackwell Science.

Dunn, E. H. & Tessaglia. D. L. 1994. Predation of birds at feeders in winter. Journal of Field Ornithology 65, 8-16.

Smith, S. 1991. The Black-capped Chickadee. Ithaca, New York: Cornell University Press.

Table 1: Raw data table of observations of chickadee feeding occurrences at the four different feeders, near and uncovered (A), near and covered (B), far and covered (C), far and uncovered (D).

Observation

Site

A

B

C

D

1

A

8

0

2

0

2

B

8

2

0

0

3

A

5

3

0

0

4

B

6

0

0

0

5

A

6

3

1

4

6

A

7

5

0

0

7

A

0

0

0

0

8

B

9

1

0

0

9

B

17

10

0

0

10

A

0

0

0

0

11

A

32

13

4.5

5

12

A

32

13

4.5

5

13

A

26

2

1.5

3

14

A

26

2

1.5

3

15

B

7

3

1.5

0

16

B

7

4

1.5

0

17

B

7

4

1.5

0

18

B

8

4

1.5

0

19

A

17

7

3

5

20

B

13

7

2

2

21

B

32

1

1

0

22

A

32

5

1

1

23

A

2

0

0

0

24

B

3

1

0

0

25

A

3

3

1

8

26

B

10

5

1

1

27

B

9

2

1

0

28

B

12

0

0

1

29

A

1

0

0

0

30

B

1

0

1

0

31

A

4

3

1

3

32

B

4

2

0

0

33

A

5

2

1

1

34

B

9

1

0

1

35

A

23

5

0

2

36

A

37

4

0

2

37

B

2

2

0

1

38

B

7

1

0

1

39

B

8

0

0

0

40

A

15

3

0

0

41

A

16

2

0

2

42

B

17

0

0

0

43

B

0

7

1

3

44

A

0

4

0

0

45

A

0

0

0

0

46

B

0

0

0

0

47

A

1

1

0

2

48

A

1

0

0

3

49

B

2

0

0

0

50

B

2

0

0

3

51

A

2

0

0

0

52

A

5

0

0

0

53

A

7

0

0

0

54

B

8

0

0

0

55

A

11

0

0

0

56

B

18

5

0

1

57

A

0

7

2

0

58

B

1

8

5

7

59

A

13

0

0

0

60

A

16

0

0

0

61

B

0

3

0

1

62

B

0

2

0

1

63

B

0

3

0

0

64

B

0

3

0

0

65

A

1

0

0

0

66

A

5

0

0

0

67

A

5

0

0

0

68

A

5

0

0

0

69

A

12

1

0

0

70

B

12

0

0

0

71

A

0

0

0

0

72

B

0

0

0

1

73

A

4

0

3

3

74

B

16

5

1

2

75

A

0

1

0

0

76

A

0

0

0

0

77

A

1

0

0

0

78

B

1

1

0.67

0

79

B

1

0

0.67

0

80

B

1

0

0.67

0

81

A

1

5

7

0

82

B

2

3

3

5

83

A

3

2

4

0

84

B

3

2

6

1

85

A

4

11

5

5

86

B

8

1

9

7

AVERAGE

7.732558

2.325581

0.953605

1.116279

Total

665

200

82.01

96

Table 1 KEY

A=near, no cover

B=near, covered

C= far, covered

D= far, no cover

Graph 1: Means plot with error bars, comparing the relationship between covered and uncovered feeders with distance to forest as well as the interaction between the two test variables by showing the average number of chickadee visits to each feeder.

x-axis- distance from forest

y-axis- average number of visits

Table 2: Statistical Two-Factor Anova Test with Replication testing the population means for both factors (distance to cover and covered/uncovered) as well as an interaction between the two factors.

Anova: Two-Factor With Replication

SUMMARY

UNCOVERED

COVERED

Total

NEAR

 

 

 

Count

86

86

172

Sum

665

200

865

Average

7.732558

2.325581

5.02907

Variance

78.31587

8.857456

50.68336

FAR

 

 

 

Count

86

86

172

Sum

96

82.01

178.01

Average

1.116279

0.953605

1.034942

Variance

3.468673

3.048725

3.246296

Total

 

 

 

Count

172

172

Sum

761

282.01

Average

4.424419

1.639593

Variance

51.66092

6.391609

ANOVA

Source of Variation

SS

df

MS

F

P-value

F crit

Sample (distance)

1371.963

1

1371.963

58.57412

2.04E-13

3.868954

Columns (metal covers)

666.9518

1

666.9518

28.47461

1.74E-07

3.868954

Interaction

591.3082

1

591.3082

25.24511

8.17E-07

3.868954

Within

7963.711

340

23.42268

Total

10593.93

343

 

 

 

 

Table 3: Statistical Regression test to determine how feeding frequency is affected by both distance from cover feeders and covered or uncovered feeders

SUMMARY OUTPUT

Regression Statistics

Multiple R

0.468906

R Square

0.219873

Adjusted R Square

0.215257

Standard Error

6.381196

Observations

171

ANOVA

 

df

SS

MS

F

Significance F

Regression

1

1939.536

1939.536

47.63143

9.9E-11

Residual

169

6881.622

40.71966

Total

170

8821.158

 

 

 

 

Coefficients

Standard Error

t Stat

P-value

Lower 95%

Upper 95%

Lower 95.0%

Upper 95.0%

Intercept

2.203867

0.582844

3.781229

0.000216

1.053274

3.354459

1.053274

3.354459

0

1.333778

0.193258

6.901553

9.9E-11

0.952268

1.715288

0.952268

1.715288

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