UCSD Primatologists Focal Sampling Methods Discussion

  

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Second part is discussion.

Original Article
Folia Primatol 2010;81:254–264
DOI: 10.1159/000322354
Received: February 24, 2010
Accepted after revision: October 19, 2010
Published onine: December 22, 2010
A Direct Comparison of Scan and Focal
Sampling Methods for Measuring Wild
Chimpanzee Feeding Behaviour
Ian C. Gilby a Amy A. Pokempner b Richard W. Wrangham a
a Department
b
of Human Evolutionary Biology, Harvard University, Cambridge, Mass., and
Wildlife Conservation Society, Bronx, N.Y., USA
Key Words
Activity budget ! Pan troglodytes ! Diet ! Frugivory ! Field methods !
Scan sampling ! Focal sampling
Abstract
Focal sampling is the most accurate method for measuring primate activity budgets but is sometimes impractical. An alternative is scan sampling, in which the behaviour of the group is recorded at regular intervals. The simplest technique is to record
whether at least 1 animal is engaged in the behaviour of interest. By direct comparison
with focal data collected simultaneously on the same population, we assess the validity
of this simple group level sampling method for studying chimpanzee (Pan troglodytes
schweinfurthii) feeding behaviour. In a 13-month study at Kanyawara, Kibale National
Park, Uganda, group level scan sampling provided statistically similar measures of broad
diet composition to those produced by focal data, despite considerable seasonal variation. Monthly means of the percentage of time spent consuming non-fig fruit calculated
from group level scan sampling were highly correlated with those from focal sampling.
This validates previous methodology used to identify periods of high energy availability. However, group level scans tended to overestimate the percentage of observation
time spent feeding, particularly for adult males. We conclude that this method of group
level scan sampling provides valuable data for characterizing broad diet choice in chimpanzees and other species, but may be of limited use for estimating individual feeding
time.
Copyright © 2010 S. Karger AG, Basel
Fax +41 61 306 12 34
E-Mail karger@karger.ch
www.karger.com
© 2010 S. Karger AG, Basel
0015–5713/10/0815–0254$26.00/0
Accessible online at:
www.karger.com/fpr
Ian Gilby, Department of Evolutionary Anthropology
Duke University, Box 90383
Durham, NC 27708 (USA)
Tel. +1 919 660 7282, Fax +1 919 660 7348
E-Mail ian.gilby @ duke.edu
Introduction
Focal sampling is generally considered to be the most accurate method for measuring primate activity budgets and is therefore the preferred method when observation conditions permit it [Altmann, 1974]. However, collecting focal data is often a
challenge for primatologists working in thick vegetation. It is particularly difficult
when studying animals that are not fully habituated to human observers (e.g. snubnosed monkeys (Rhinopithecus roxellana) [Guo et al., 2007]), or arboreal species in
which individuals cannot be quickly or reliably identified (e.g. woolly monkeys
(Lagothrix lagotricha) [Di Fiore and Rodman, 2001] or Sulawesi crested black macaques (Macaca nigra) [O’Brien and Kinnaird, 1997]). One alternative to focal animal sampling is scan sampling [Altmann, 1974], which involves recording the behaviour of all visible individuals at predetermined intervals. Numerous variants of scan
sampling have been used to calculate basic parameters such as activity budgets and
diet composition in many primate populations.
At our study site at Kanyawara, Kibale National Park, Uganda, scan sampling
has repeatedly been used to identify seasonal variation in the diet of chimpanzees
(Pan troglodytes schweinfurthii) [Conklin-Brittain et al., 1998; Gilby and Wrangham,
2007; Emery Thompson and Wrangham, 2008]. The chimpanzees in this community rely on ripe fig fruits (Ficus spp.) as a ‘fall-back’ food [Wrangham et al., 1993;
Marshall and Wrangham, 2007] which they consume during periods of low food
availability. Their ‘preferred’ foods (defined as those that are selected disproportionately often relative to their abundance [Leighton, 1993; Marshall and Wrangham,
2007]) are ripe drupe fruits, also referred to as ‘non-fig fruits’ (NFF). In these studies, the relative contribution of NFF (or other foods) to the diet was assessed from
scans in which observers recorded whether at least 1 chimpanzee in the group was
feeding on a given item. This simple measure of feeding behaviour is similar to one
used by Fragaszy et al. [1992], who classified squirrel monkeys as ‘foraging together’
if at least 1 individual in the social group was ‘engaged in a food-related activity’. NFF
consumption by the Kanyawara chimpanzee community, as assessed by this sampling method, appears to be a salient correlate of behaviour, probably because it indexes energy availability. Thus, it has been linked to higher food quality [ConklinBrittain et al., 1998], higher C peptide production [Emery Thompson et al., 2009],
larger subgroups [Wrangham, 2002], increased reproductive function in females
[Emery Thompson and Wrangham, 2008] and higher rates of hunting and killing
red colobus monkeys (Procolobus spp.) [Gilby and Wrangham, 2007]. We suspect
that NFF consumption is also important in other chimpanzee communities as well
as other frugivorous primates. Before this claim can be tested, however, our simple
group level measure of NFF diet composition must first be validated.
Group level scan sampling is vulnerable to various potential problems. First, if
feeding activity is not synchronous for all members of a group, group level scans will
overestimate the total time an average individual spends feeding. Second, if the behaviour of some individuals is oversampled, and there is substantial individual variation in diet choice, group level scans would be unrepresentative of individual food
intake. Therefore, group level scan sampling would neither capture intraspecific
variation in feeding behaviour (such as variation associated with age or sex class) nor
represent a meaningful average (across ages or sexes). For chimpanzees, these effects
are plausible because compared to males, females often feed in smaller groups and
Measuring Chimpanzee Feeding Behaviour
Folia Primatol 2010;81:254–264
255
visit large feeding parties for shorter periods [Wrangham and Smuts, 1980]. If the
strength of such an effect varies among food types, group level scans might lead to a
distorted picture of seasonal variation in food intake.
Here we assess the importance of such problems by comparing the results of
group level scan sampling with data collected using focal sampling during the same
period. We assume that focal sampling provides accurate and reliable data. We assess
the validity of group level scan data by comparison with focal data collected on (a)
overall feeding time and (b) diet composition. We use these data to test the hypothesis that a group level sampling protocol is sufficient for identifying temporal variation in feeding behaviour.
Methods
Study Population
The Kanyawara chimpanzee community resides within Kibale National Park, Uganda,
and has been studied continuously by Richard Wrangham and colleagues since 1987 [Wrangham et al., 1991, 1992]. The chimpanzees were habituated to the presence of researchers without
provisioning. The community composition has remained relatively stable over the course of the
long-term study, averaging 40–50 individuals, with 9–12 adult males and 12–15 adult females
[Gilby and Wrangham, 2008].
Party Level Scan Sampling
Since 1987, the Kibale Chimpanzee Project (KCP) has conducted daily follows of the Kanyawara chimpanzees. For the current study, we used data collected by KCP researchers between
June 1, 2004, and June 30, 2005. Most days, a team of observers consisting of at least 2 Ugandan
field assistants, typically accompanied by graduate students, the project manager or visiting
scientists, located a party of chimpanzees by using the previous day’s nesting data, checking
recent feeding trees and/or listening for calls. Chimpanzees have a fission-fusion social organization in which individuals form fluid groups (parties, hereafter) containing a subset of the
community [Nishida, 1968; Wrangham and Smuts, 1980; Goodall, 1986]. The research team
followed the party for as long as possible, usually from dawn until dusk. If the party split, the
observers followed the larger subgroup, unless there were enough researchers to follow both
parties. In that case, both parties were followed simultaneously.
At 15-min intervals, one observer used instantaneous scan sampling [Altmann 1974] (‘party level scans’, hereafter) to record party composition and feeding behaviour. If at least 1 chimpanzee in the party was feeding (consuming food), the observer recorded the species and part
(e.g. fruit, leaf) that was being eaten. This method was designed to capture broad dietary patterns, therefore the observer did not record which chimpanzees were feeding. In cases in which
members of the party were feeding on different food items, the observer recorded the food eaten
by the majority of the individuals that were feeding. All data were digitized and stored in a relational database in the Department of Human Evolutionary Biology at Harvard University.
From these data, we calculated 2 monthly measures of feeding behaviour. First, we calculated time spent feeding – the percentage of all party level scans in which at least 1 chimpanzee
was feeding. Second, we calculated NFF diet composition – the percentage of all feeding scans
in which chimpanzees were consuming NFF [Gilby and Wrangham, 2007; Emery Thompson
and Wrangham, 2008].
Focal Sampling
During the same time period (June 1, 2004, to June 30, 2005), one of the authors (A.A.P.)
conducted focal sampling [Altmann, 1974] of individual chimpanzees as part of a concurrent
study on sex differences in feeding behaviour [Pokempner, 2009]. Focal individuals included 5
adult males and 5 non-cycling (i.e. pregnant or lactating) adult females. During full-day focal
256
Folia Primatol 2010;81:254–264
Gilby /Pokempner /Wrangham
follows, the activity of the individual was recorded using instantaneous scan sampling [Altmann, 1974] at 1-min intervals. When the focal individual was feeding, the species, plant part
and phytophase (e.g. ripe, unripe, young, mature) of the food were recorded. Due to the nature
of fission-fusion grouping, it was not always possible to rotate focal individuals in a systematic
fashion. A field assistant was therefore assigned to follow a selected individual until the end of
the day in order to locate them as a focal for the following day. This strategy was intended to
reduce the potential bias of following larger parties and resulted in focal follows that were sometimes conducted in the absence of KCP observers. Focal follows averaged 9.2 h and were distributed evenly by sex and season. We calculated time spent feeding and NFF diet composition using the focal data in the manner described for the party level scans.
Analysis
First, we used linear regression to examine whether monthly means of time spent feeding
and NFF diet composition calculated from focal sampling data were predicted by those calculated from party level scan sampling. We assumed that a statistically significant association, a
slope of 1, and a high R 2 value indicated that data collected by party level scan sampling provided a meaningful estimate of data collected by focal sampling. Second, for each of the 2 variables (time spent feeding and NFF diet composition), we calculated the difference between the
monthly means derived from party level and focal sampling, and used a 1-sample t test to ascertain whether the difference was significantly different from zero. This allowed us to evaluate
the magnitude of any discrepancy between the 2 data collection methods. Finally, we used logistic regression to estimate the probability that if at least 1 member of the party was feeding on
NFF (as determined by a party level scan), the focal individual was also doing so. This provided
a means of evaluating the degree to which members of a feeding party were consuming the same
type of food. We ran our analyses on both sexes together as well as separately. We conducted all
statistical analyses using SAS 9.2 (SAS Institute, Cary, N.C., USA).
Results
The KCP research teams conducted 15,602 15-min party level scans during the
13-month study period, equalling 3,900.5 h of observation. There were 103 instances when 2 research teams sampled the same chimpanzee party, usually when 2 simultaneously followed parties briefly came together. For each of these, we randomly deleted one of the observations, resulting in 15,499 party level scans (table 1). At
least 1 chimpanzee was feeding in 58.2% (9,025) of these scans. Chimpanzees were
feeding on non-fig fruits (NFF) in 39.6% (3,577) of feeding scans. Monthly values of
time spent feeding are displayed in table 1.
81,294 1-min focal scans were conducted during the study period, equalling
1,354.9 h of observation (table 1). The focal chimpanzee was feeding in 32.9% (26,748)
of these scans. NFF was being consumed in 37.4% (10,010) of focal feeding scans.
5,424 of the 1-min focal scans occurred on the quarter-hour (0, 15, 30 or 45 min
after the full hour). The focal chimpanzee was in a party being sampled by a KCP
research team for 3,650 (67.3%) of these 15-min scans (table 2). These are our ‘simultaneous’ data points for which data could be matched between the focal and party
level scans. Our statistical analyses used these data points.
According to the KCP party level data, at least 1 chimpanzee was feeding in
63.2% (2,308/3,650) of the simultaneous scans. By contrast, the focal chimpanzee
was feeding in 33.7% (1,230/3,650) of the simultaneous scans. Estimates of NFF diet
composition based on party level and focal sampling were similar, however. The focal chimpanzee was feeding on NFF in 39.8% (490/1,230) of focal feeding scans,
Measuring Chimpanzee Feeding Behaviour
Folia Primatol 2010;81:254–264
257
258
Table 1. Summary of the complete data set
Year
Folia Primatol 2010;81:254–264
Gilby /Pokempner /Wrangham
2004
2004
2004
2004
2004
2004
2004
2005
2005
2005
2005
2005
2005
Month
June
July
August
September
October
November
December
January
February
March
April
May
June
All months
Party level scans (15-min intervals)
observation
feeding
scans
hours
scans
1,118
1,316
1,417
1,439
1,289
1,045
881
1,212
1,161
1,114
1,118
1,279
1,110
279.5
329
354.3
359.8
322.3
261.3
220.3
303
290.3
278.5
279.5
319.8
277.5
703
754
939
870
790
587
455
739
670
637
517
720
644
62.9
57.3
66.3
60.5
61.3
56.2
51.6
61.0
57.7
57.2
46.2
56.3
58.0
15,499
3,874.8
9,025
58.2
% total
scans
Focal scans (1-min intervals)
NFF feeding
observation
feeding
NFF feeding
scans
% feeding
scans
scans
hours
scans
% total
scans
scans
% feeding
scans
460
289
157
595
553
249
108
178
161
429
281
23
94
65.4
38.3
16.7
68.4
70.0
42.4
23.7
24.1
24.0
67.3
54.4
3.2
14.6
2,448
7,421
7,165
5,159
10,163
2,584
6,711
9,200
5,551
6,214
6,572
8,327
3,779
40.8
123.7
119.4
86.0
169.4
43.1
111.9
153.3
92.5
103.6
109.5
138.8
63.0
649
3,037
3,318
1,573
3,130
859
2,010
3,050
1,691
2,048
1,575
2,471
1,337
26.5
40.9
46.3
30.5
30.8
33.2
30.0
33.2
30.5
33.0
24.0
29.7
35.4
481
943
482
1,040
2,122
357
699
888
583
1,303
1,003
88
21
74.1
31.1
14.5
66.1
67.8
41.6
34.8
29.1
34.5
63.6
63.7
3.6
1.6
3,577
39.6
81,294
1,354.9
6,748
32.9
10,010
37.4
Party level scans occurred at 15-min intervals and were classified as ‘feeding’ if at least 1 chimpanzee in the party was feeding at the time of the scan,
and as ‘NFF feeding’ if NFFs were being consumed. Focal observations took place at 1-min intervals and were classified in the same manner as party
level scans.
Table 2. Simultaneous 15-min focal and party level scans of the same chimpanzee party, by month
Year
2004
2004
2004
2004
2004
2004
2004
2005
2005
2005
2005
2005
2005
Month
June
July
August
September
October
November
December
January
February
March
April
May
June
All months
Total
scans
NFF feeding scans
Feeding scans
focal
party
focal
party
scans
% total
scans
scans
% total
scans
scans
% feeding
scans
scans
% feeding
scans
128
276
360
295
460
99
206
447
274
311
266
366
162
33
117
163
94
140
34
70
147
85
103
71
115
58
25.8
42.4
45.3
31.9
30.4
34.3
34.0
32.9
31.0
33.1
26.7
31.4
35.8
97
161
259
193
308
58
116
286
185
201
131
204
109
75.8
58.3
71.9
65.4
67.0
58.6
56.3
64.0
67.5
64.6
49.2
55.7
67.3
26
42
18
71
101
23
26
37
28
70
47
1
0
78.8
35.9
11.0
75.5
72.1
67.6
37.1
25.2
32.9
68.0
66.2
0.9
53
65
46
147
222
34
35
65
43
149
87
3
2
54.6
40.4
17.8
76.2
72.1
58.6
30.2
22.7
23.2
74.1
66.4
1.5
1.8
3,650
1,230
33.7
2,308
63.2
490
39.8
951
41.2
‘Feeding scans, focal’ = the number (and percentage) of total scans when the focal chimpanzee was
feeding; ‘feeding scans, party’ = the number (and percentage) of total scans when at least 1 chimpanzee in
the party was recorded as feeding, according to party level scan sampling; ‘NFF feeding scans, focal’ = the
number (and percentage) of feeding scans when the focal chimpanzee was consuming NFF; ‘NFF feeding
scans, party’ = the number (and percentage) of feeding scans when at least 1 chimpanzee was recorded as
eating NFF.
while at least 1 chimpanzee was feeding on NFF in 41.2% (951/2,308) of the party
level feeding scans.
These data suggest that our party level scans provided a close approximation of
broad diet composition but not of individual time spent feeding. Below we use the
monthly variation to assess this claim.
Time Spent Feeding
There was no correlation between monthly means of time spent feeding when
party level and focal data were compared (F1, 12 = 0.12, R 2 = 0.01, p = 0.74, fig. 1, open
circles). The mean difference between time spent feeding calculated from party level
data and focal data was 29.7 (range 15.9–50), which was significantly greater than zero
(1-sample t test, T1, 12 = 12.44, p ! 0.0001; fig. 2, open circles). This indicates that our
party level sampling method consistently overestimated individual feeding times.
When the focal chimpanzee was male, there was no correlation between estimates of time spent feeding calculated from party level and focal data (F1, 12 = 1.12,
R 2 = 0.01, p = 0.31; fig. 3a, open circles). For females, however, this relationship was
statistically significant (F1, 12 = 4.83, R 2 = 0.24, slope = 0.50 8 0.23 (SE), p = 0.05;
fig. 3b, open circles).
Measuring Chimpanzee Feeding Behaviour
Folia Primatol 2010;81:254–264
259
Monthly means (focal sampling)
100
NFF diet composition (% feeding scans)
Time spent feeding (% total scans)
R2 = 0.91
Slope = 1.02 ± 0.09
p < 0.0001 90 80 70 60 50 40 R2 = 0.01 p = 0.74 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 Monthly means (party level sampling) Fig. 1. Correlation between monthly means calculated from simultaneous focal and party level Party level values minus focal values scans. Solid diamonds represent NFF diet composition, which equals the percentage of feeding scans in which NFF was being consumed. Open circles represent time spent feeding, which equals the percentage of scan samples in which feeding was recorded. See text for details. 80 NFF diet composition (% feeding scans) Time spent feeding (% total scans) 60 40 20 0 –20 –40 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Month of study Fig. 2. Differences between monthly means derived from party level and focal sampling. Solid diamonds represent NFF diet composition values derived from party level sampling minus those derived from focal data. Open circles represent time spent feeding (party level sampling) minus time spent feeding (focal data). Diet Composition There was a strong positive correlation between estimates of monthly NFF diet composition (percent of feeding time eating NFF) calculated from focal and party level sampling (F1, 12 = 121.4, R 2 = 0.91, slope = 1.02 8 0.09, p ! 0.0001; fig. 1, solid diamonds). The estimated slope of the NFF regression line (range 0.93–1.11) includes 1, indicating that party level scan sampling corresponded well with focal-based data 260 Folia Primatol 2010;81:254–264 Gilby /Pokempner /Wrangham Monthly means (focal sampling) 100 NFF diet composition (% feeding scans) Time spent feeding (% total scans) 90 80 R2 = 0.96 Slope = 0.98 ± 0.06 p < 0.0001 70 60 50 40 30 R2 = 0.01 p = 0.31 20 10 0 0 a Monthly means (focal sampling) 100 10 20 30 40 50 60 70 80 90 100 Monthly means (party level sampling) NFF diet composition (% feeding scans) Time spent feeding (% total scans) 90 R2 = 0.67 Slope = 0.87 ± 0.17 p = 0.0004 80 70 60 50 40 R2 = 0.24 Slope = 0.50 ± 0.23 p = 0.05 30 20 10 0 0 b 10 20 30 40 50 60 70 80 90 100 Monthly means (party level sampling) Fig. 3. Correlations between monthly means calculated from simultaneous focal and party level data for male (a) and female focal animals (b). Solid diamonds represent NFF diet composition, and open circles represent time spent feeding. on seasonal variation in food choice. The mean difference between values of NFF diet composition determined by the 2 methods was –2.4 (range –24.1 to 6.7), which was not significantly different from zero (1-sample t test, T1, 12 = –1.26, p = 0.23; fig. 2, solid diamonds). Finally, party- and focal-based estimates of NFF diet composition were very strongly correlated when the focal chimpanzee was an adult male (F1, 12 = 316.7, R 2 = 0.96, slope = 0.98 8 0.06, p ! 0.0001; fig. 3a, solid diamonds). When the focal chimpanzee was a female, the correlation between party- and focal-based estimates of NFF diet composition was also highly significant, but not as tight (F1, 12 = 25.74, R 2 = 0.67, slope = 0.87 8 0.17, p = 0.0004; fig. 3b, solid diamonds). The lower R 2 was due to a single month (June 2004) in which the focal-based NFF diet composition (70%) was more than 4 times greater than the party-based NFF diet composition (16%). During this month, there were only 18 simultaneous focal and party level feeding scans when the focal chimpanzee was an adult female. This is more than Measuring Chimpanzee Feeding Behaviour Folia Primatol 2010;81:254–264 261 Probability that focal was feeding on NFF Party feeding on NFF Party feeding on ‘other’ food type 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 0 5 10 15 Adult party size 20 Fig. 4. Graphical representation of the results of a multiple logistic regression modelling the probability that the focal chimpanzee was feeding on NFF. The focal individual was significantly more likely to be feeding upon NFF in parties that were classified as feeding on NFF (solid diamonds) than in parties that were consuming another type of food (open circles). As party size increased, however, the focal individual was significantly less likely to be feeding upon the same broad food category as the party. Error bars represent 95% confidence intervals of the regression lines. 1 standard deviation below the mean number of such scans during the other months of the study (38 8 16). Nine (50%) of the scans occurred during a single feeding bout in which the party was recorded as eating terrestrial herbaceous vegetation, and focal female BL was recorded to be eating Uvariopsis congensis, an important NFF. When we removed June 2004 from the analysis, the R 2 value increased to 0.92 (F1, 11 = 135.22, slope = 0.99 8 0.085, p ! 0.0001). There were 1,021 instances in which both the party and the focal individual were classified as feeding. In this sample, the focal chimpanzee was significantly more likely to be feeding upon NFF if we had classified the group as feeding on NFF (an ‘NFF feeding party’) than if the party was feeding on something else (GEE logistic regression, odds ratio = 84.7, !21 = 545.2, p ! 0.0001, repeated measure = focal). However, in 40 (10.3%) of the 388 instances in which the party was consuming NFF, the focal animal was eating another food item. As the size of an NFF feeding party increased, this discrepancy increased (multiple logistic regression, odds ratio = 1.04, !21 = 4.33, p ! 0.0001, repeated measure = focal). In the largest NFF feeding parties (19 adults), there was an 86% chance that the focal chimpanzee was also eating NFF (fig. 4). Note that in NFF feeding parties containing only 1 adult, the probability that the focal individual was consuming NFF was only 93% (not 100%). This is likely due to the fact that our party level scan samples included subadults, which may have been eating NFF while the focal adult was consuming something else. When included in the multiple logistic regression, the focal individual’s sex did not have a significant effect on the probability that s/he was feeding upon NFF (!21 = 1.2, p = 0.27). 262 Folia Primatol 2010;81:254–264 Gilby /Pokempner /Wrangham Discussion We found that a broad group level measure of chimpanzee diet composition correlated closely with data collected on focal individuals. Specifically, monthly measures of non-fig fruit (NFF) diet composition derived from group level scan sampling (in which a group was classified as ‘feeding’ if at least 1 chimpanzee was doing so) were highly correlated with those derived from focal sampling. This finding validates previous methodology used to identify periods of high energy availability at Kanyawara [Gilby and Wrangham, 2007; Emery Thompson and Wrangham, 2008]. However, our data suggest that this correlation should be interpreted with caution. While the difference between monthly values derived from group level scans and focal data were not significantly different from zero, there were some months in which there was a considerable discrepancy. For example, in June 2005, the group level data yielded an estimate of NFF diet composition (14.6%) that was more than 9 times greater than that based on focal data (1.6%). However, in other months, the estimates were almost identical (e.g. November 2004 and May 2005). This variability is likely due to the possibility that members of a social group may be feeding upon different food items. While the focal chimpanzee was highly likely to be consuming NFF if the group was classified as doing so, s/he was eating another food item roughly 10% of the time. This discrepancy increased with adult group size. Whether or not this level of accuracy is acceptable will depend on the nature of the question being addressed. Data from group level scan sampling did not provide an accurate estimate of an individual’s time spent feeding, as determined by focal animal sampling. Similarly, Fragaszy et al. [1992] found that in comparison to focal sampling, group scan sampling overestimated the amount of time spent feeding by wedge-capped capuchins (Cebus olivaceus) and squirrel monkeys (Saimiri oerstedi). In our study, this result is not surprising, since a group was classified as ‘feeding’ if a minimum of 1 chimpanzee was feeding at the time of the scan. However, the group level scan data provide a rough idea of female feeding times. One possible explanation for this is that sampling of females might have been more likely in smaller parties, in which the chances are higher that all group members are engaged in the same behaviour. This possibility remains to be tested. In sum, our data showed that group level scan sampling provided accurate measures of broad diet composition, including seasonal variation. It did not closely predict the percentage of time spent feeding however, suggesting that, when possible, focal sampling should be used for estimating individual feeding rates. While our results are derived from a single chimpanzee community, their fit to expectation suggests that they may have wide applicability to primate studies. In circumstances where focal sampling is impractical, a simple group scan sampling protocol is valuable for identifying broad temporal variation in individual diet composition. Acknowledgments Long-term research at Kanyawara was supported by funding from NSF Grant 0416125 to R.W.W.; I.C.G. was also partially supported by NSF Grant IIS-0431141. A.A.P. received funding from the L.S.B. Leakey Foundation, the American Society of Primatologists, Sigma Xi, Stony Measuring Chimpanzee Feeding Behaviour Folia Primatol 2010;81:254–264 263 Brook University and the Wildlife Conservation Society. We thank the Uganda National Council for Science and Technology, the Uganda Wildlife Authority and the Makerere University Biological Field Station for permission to conduct research within Kibale National Park. This project would not have been possible without the hard work and dedication of the members of the field research team employed during the study period, especially Francis Mugurusi, Solomon Musana and field manager Alain Houle. This study complied with the ethical guidelines of the National Science Foundation, Harvard University (Animal Experimentation Protocol No. 96-03), Stony Brook University (Institutional Animal Care and Use Committee No. 20041349) and the laws of Uganda. This manuscript was significantly improved due to the advice of 3 anonymous reviewers. 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Wrangham RW, Clark AP, Isabirye-Basuta G (1992). Female social relationships and social organization of Kibale Forest chimpanzees. In Topics in Primatology (Nishida T, McGrew WC, Marler P, Pickford M, de Waal FBM, eds.), vol 1: Human Origins, pp 81–98. Tokyo, Tokyo University Press. Wrangham RW, Conklin NL, Chapman CA, Hunt KD (1991). The significance of fibrous foods for Kibale Forest chimpanzees. Philosophical Transactions of the Royal Society of London Series B Biological Sciences 334: 171–178. Wrangham RW, Conklin NL, Etot G, Obua J, Hunt KD, Hauser MD, Clark AP (1993). The value of figs to chimpanzees. International Journal of Primatology 14: 243–256. 264 Folia Primatol 2010;81:254–264 Gilby /Pokempner /Wrangham These are two different things for the same article First: Reading summaries should be a half page (~250 words) description of objectives, brief methodology, results, and interpretation of results. Some studies will have more in the way of a clear experimental process, where others will be more of a review – yet these “review-type” papers still have methodologies to convey their results. 1. 1-2 sentence intro: This should be a quick description of the idea covered in the reading (e.g. Scientific experimentation can be subdivided into lab studies, field studies, and natural experiments. Diamond et al. posit the idea.). 2. Objective or purpose of experiment/observational study/writing – what is the purpose and to convey what message? 3. Results/conclusions. Highlight the key findings and take-home messages. 4. Your interpretation of these results and/or if this is a relevant contribution. – Your interpretation is subjective, so feel free to write a comment in a subjective fashion! Second part: What are your thoughts of the reading? This could include aspects of what you liked/disliked, agreed/disagreed with, or even things you may have had difficulty in understanding. In order to receive full points, your entry should be 3-4 sentences long and you have to reply at least once to someone else's entry. The objective is for you to begin to think as an emerging expert. A good way to accomplish this is to begin to challenge and/or think critically of the author’s decisions in experimental design and conclusions drawn from the data. I want you to think about if you would do things this way or draw the same conclusions – think “does it make sense?” and why/why not. Purchase answer to see full attachment