1
Supplementary Material
Piotr G. Jablonski1,2, Sang-im Lee1, 3, Elzbieta Fuszara4, Maciej Fuszara4, Choongwon Jeong1&
Won Young Lee1*
Proximate mechanisms of detecting nut properties in a wild
population of Mexican Jays (Aphelocoma ultramarina)
1
Laboratory of Behavioral Ecology and Evolution, School of Biological Sciences, College of Natural Sciences,
Seoul National University, Seoul, 151-742, Republic of KOREA
2
Museum and Institute of Ecology, Polish Academy of Sciences, Warsaw, POLAND
3
Institute of Advanced Machinery and Design, Seoul National University, Seoul 151-742, Republic of KOREA
4
University of Warsaw, Faculty of Biology, Department of Animal Physiology, ul. Miecznikowa 1, 02-096
Warszawa, POLAND
& Current affiliation: Depatment of Human Genetics, University of Chicago, Chicago, 920 E. 58th Street, CLSC,
Chicago, IL 60637, USA
*
Current affiliation: Division of Polar Life Sciences, Korea Polar Research Institute, Incheon 406-840, Republic of
KOREA
Corresponding author:
Sang-im Lee; snulbee@behecolpiotrsangim.org
2
Classification of head and beak movements from slow motion videos
We used a Troubleshooter high speed camera
(250 fps; occasionally 500 and 1000 fps) to
capture the details of handing of peanuts by the
Mexican jays. These movies were analyzed to
quantify the behavior of handling the nuts by
jays. First, we noted if handling was associated
with beak opening (and subsequent closing), and
how many beak opening-closing movements
were present in each handling event. The results
are shown in Fig. S1.
Fig. S1. Frequency of beak opening-closing during
handling of peanuts in a jay group at Cave Creek Canyon
(n=174).
3
Effect of mass on nut acceptance (Experiments 1, 2 and 3) – additional
variables and interpretations
Experiment 1 – Effect of mass on nut acceptance I (empty vs normal)
Normal peanuts were taken on average earlier from the feeding arena than empty ones
(Supplementary Fig. S2A; Latency till Acceptance, F1, 64 = 9.44, P=0.0031). This is also
represented in the smaller Number of Rejections for normal than for empty peanuts (Fig. S2B; F1,
90 = 84.27, P<0.0001).
Experiment 2 – Effect of mass on nut acceptance II (heavy vs normal)
Analysis focusing on nuts.
Heavy peanuts were taken away on average earlier from the feeding arena than normal ones (Fig.
S2C; Latency till Acceptance, F1, 658 = 15.43, P<0.0001). This preference for heavy peanuts was
also represented in smaller Number of Rejections (Fig. S2D) for heavy than for normal peanuts
(F1, 658 = 161.94, P<0.0001).
Although we took care of removing any traces of clay that might have occurred on the
exterior of the shell during the experimental preparation of the heavy peanuts in the Experiment
2, the jays seemed to be able to discriminate the two types of peanuts based on the appearance
and they delayed picking up heavy peanuts in comparison to normal peanuts. As an ad-hoc
explanation, we suspect that it was a narrow streak of white clay that might have been visible in
some nuts along the seam where the two shell halves have been glued together. This suggests
that before choosing a nut for handling the jays are carefully paying attention not only to the
visual size but also to much finer details on the shell surface, similar to blue jays paying attention
to the presence of artificial hole in an acorn (Bossema 1979). Despite their initial lower attraction
to heavy peanuts, which resulted in delayed handling, heavy peanuts were accepted sooner and
more readily during handling than normal ones. Hence, the cues perceived during handling have
overridden the initially lower visual attraction to the heavy peanuts.
Analysis focusing on birds.
Analysis of all lifts by birds revealed that the birds accepted heavy peanuts more easily than
normal peanuts (Fig.S3A, F1, 1698 = 37.56, P<0.0001).
4
Experiment 3 – Effect of vision on nut acceptance (single vs triple)
Once a peanut was lifted the Latency till Acceptance was shorter for the visually smaller singles
than for the triples (Fig. S2E, F1, 159=11.09, P=0.0011). Also, the visually smaller peanuts were
rejected less often (Nr of Rejections was smaller for singles than for triples; Fig. S2F, F1,
166=42.46, P<0.0001) than were the visually larger peanuts.
Fig. S2. Effect of experimental peanut type on the least square means and their standard errors of
the Latency till Acceptance (A, C, E), and the Number of Rejections (B, D, F) in Experiment 1 (A, B),
Experiment 2 (C, D) and Experiment 3 (E, F).
5
Is there an effect of repeated presentations of heavy and normal
peanuts on the preference for heavier peanuts?
The clay in heavy peanuts in the Experiment 2 was dried in order to avoid scent cues. This also
resulted in the nuts inside the shell being solidly set inside the dry clay. Although the nut meat
content of both, normal and heavy, peanuts was the same, the handling time and difficulty in
extracting the nuts from the heavy peanuts was larger due to the presence of hardened clay (the
birds seemed not to be deterred by the clay as long as the saw nuts embedded in it). Based on
direct observations of several individuals we knew that it takes longer time to extract nuts from
heavy peanuts. Using individual-bird based analyses (see Methods in the paper), we tested the
hypothesis that birds may learn over time that the heavier nuts may be less profitable. We
Fig. S3. Acceptance rate of heavy and normal peanuts in Experiment 2 for all the lifts (A) by
individually marked birds in five flocks (Gate, Corral, Hillside, Kitchen and Tank), and the effect of
repeated testing over 5 days on the acceptance of heavy and normal peanuts by individually marked
birds in KI flock (B). Least square means are written above the bars. Letters “a” and “b” indicate that
the two types of peanuts differ statistically significantly from each other.
thought this was possible because at least some of the caches appeared to be rather temporary
and jays were observed to uncover their recently hidden food items (Jablonski PG, Lee SI,
Fuszara M, Fuszara E, personal observation). Additionally, some caches were pilfered by other
individuals soon after they were made (Jablonski PG, Lee SI, Fuszara M, Fuszara E, personal
observation). Hence, we suspected that the jays may learn over time the association between
peanut properties and its content and change their behavior at the feeding arenas after repeated
feeding trials. Therefore, using the data set for one flock (Kitchen) that has been tested multiple
times for 5 days during one week (tests on 12th, 15th, 16th, 18th, and 19th of February, 2009),
we tested the effect of “Day” (five rank values: 1, 2, 3, 4, 5) on the acceptance of heavy versus
normal peanuts. Contrary to our expectations, the birds did not change their preference for heavy
peanuts (Fig. S3B; effect of interaction day*peanut type F1, 1105 = 0.21, P=0.64; effect of day F1,
1105 = 1.97, P=0.16), indicating the robustness of the bird preferences for heavier nuts.
6
Sound of peanuts and their acceptance by jays
The different types of peanuts used in the Experiment 1, 2 and 3 differed in sound produced
when a beak (or a chopstick as in our first attempts to characterize the sound differences among
peanuts: Fig. S4) hits the shell.
Preliminary analyzes from
partial data sets confirm that
when peanuts differ in the
sound but do not differ in mass,
size and look, jays are able
differentiate between them in
experimental feeding arena
(Jablonski PG, Lee SI, Fuszara
M, Fuszara E, in preparation).
This indicates that they pay
attention to sound and use it as
one of the cues in deciding
which nut to accept and which one
Fig. S4. Examples of sounds given by a peanut filled
to reject.
with nuts (A, B) and a peanut without nuts inside a shell
(C, D) hit by a chopstick