Evidence of teaching in spotted Dolphins Bender et Al.(2009)

1. Evidence of teaching in spotted Dolphins Bender et Al.(2009) Presented by Kate and Juliann.

2. Summary • This paper reviewed videos of Atlantic Spotted Dolphins with and without their calves to look for evidence of teaching while the pairs were foraging. • To do this, they looked at chase latencies (time between rooting up the prey and chasing it) and also the number of body-orienting movements. • They also monitored the position of the young relative to the mother.

3. Background • Definition of teaching by Caro and Hauser (1992) • “An individual actor A can be said to teach if it modifies its behavior only in the presence of a naïve observer, B, at some cost or at least without obtaining an immediate benefit for itself… As a result, B acquires knowledge or learns a skill earlier in life or more rapidly or efficiently than it might otherwise do, or that it would not learn at all.”

4. Background • Some behaviors are transmitted culturally by teaching, such as foraging • Other species that have shown this are primarily Cetaceans and Chimpanzees. But other species have evidence of this as well. • However, observations of mother-infant teaching are rare, and tend to be anecdotal

5. Methods - Dataset • In the current study an analysis was performed on video recordings of the Atlantic spotted dolphin. These videos have been collected by the Wild Dolphin Project since 1985 by an island off the coast of Florida. • The videos have clear water, visibility up to 90ft, and the dolphins have been individually identified and sexed.

6. Methods - Dataset • This study used videos specifically from 1991 to 2004. Videos were selected from this sample with the following requirements: • Individuals were identifiable. • The end and the beginning of the chase were observed. • Prey was visible in the video. • When a calf was present it must be within proximity of 2 body lengths. • When a calf was present it must be in an identifiable position relevant to the mother.

7. Fig 1 Methods - Subjects • Atlantic spotted dolphins can be categorized into age groups by their spot patterns, with newborns having no spots. (Fig 1) • Calves were aged by previous sighting of a pregnant female, followed by a sighting with a suckling calf. • Between these two methods the calves were assessed to be no more than 3 years old. • Weaning starts after year 3, so in this way they were all still nursing and dependent on their mother’s milk for nutrition.

8. Methods – Foraging Events • For the purpose of this study Benthic foraging behavior was used for observation, and defined into a series of behaviors performed by the subject. • Foraging events included; • Scanning • Rooting/Digging • Chasing • And ingestion.

9. Methods – Factors • These foraging events were analyzed for two factors; chase latency (CL) and Body-orienting movements (BOM). • CL is the length of time the prey is pursued from the prey-object appearing from the sand, to the point where it is ingested or no longer pursued. • BOM is the dolphin’s attention to the prey-object. A BOM is measured when a dolphin moves its body in the direction of the prey object. • CL and BOM were measured in three kinds of clips. • A) Videos with calves present, • B) Videos of mothers by themselves, and • C) videos with mothers seen with a conspecific. (Control) • Finally, calves were recorded to in one of five different named positions while with their mother; • Echelon, • infant, • head-under-head, • observation, • or ‘other’.

10. Methods - Data • A total of 38 video segments were used. • 14 of these were with calves present. • 24 without calves present. • 3 of these were with conspecifics. • A total of 10 calves were observed. • And a total of 9 mothers (one seen with two different calves) • 10 of the 22* videos occurred while the female subject was considered a juvenile. (Prior to sexual maturity)

11. Mother without calf:

12. Mother with calf:

13. Results – Chase Latency (CL) • Mothers with calves chased the prey significantly longer than when calves were not present.

14. Results – Chase Latency (CL)

15. Results – Body Orienting Movements (BOM) • BOM were made significantly more often as a group when the mother was foraging with her calf than without. • 6 of the 9 mothers were found to do this. • Little gash, Nippy, and Rosemole did not display any BOM changes in the presence of calves.

16. Results - Other • Cross generational comparisons are briefly mentioned, but with only one sample. • They showed the same changes foraging behavior, unsurprisingly. • The Foraging with non-calf individuals was also analyzed as a means of control. • Only 3 instances, which proved too small to perform a statistical analysis. • When comparing the 3 results to the results of the same individuals foraging with calves and without, they found them to be comparable to those without calves.

17. Additional Analyses – Prey species • Chase Latencies and Body-Orienting movements were not different between prey-types. • Researchers identified prey type in 14 observations; Snakefish, flounder, and razor fish. • The mean CL and BOM were not significantly different for any of the species and found no correlation. • Researchers analyzed another 10 foraging events with different individual dolphins • There was no difference in the CL or BOM with these subjects in comparison to mothers foraging without calves.

18. Additional Analyses – Age of subjects • Researchers found no significant correlation between the age of the calf and CL or BOM. • The age of the mothers was not significant in CL, but it was statistically significant with the BOM. • Older mothers made fewer BOM than did younger mothers.

19. Additional Analyses – Experience of mothers • Individual mothers that were observed as juveniles were compared to later videos of the same individuals as adults. • There were no significant changes in CL or BOM between ages of specific individuals. • 3 of the mothers were observed with and without their calves within the same year.

20. Additional Analyses – Calf position • As mentioned earlier the positions of the calves were recorded with each of the 14 with-calf-videos. • Some of the videos showed multiple calf positions. • The most common position was the “observation” position.

21. Additional Analyses - Ingestion • The data in which ingestion by the mother was known (either by being present in the video or first-hand account) was analyzed. • 5 mothers were observed not eating prey. • This occurred in 5 out of the 38 events recorded. • All of these were in the 14 trials with calves present. • In each of the 5 cases calves were allowed to pursue the prey. • In 3 of these calves were confirmed to have eaten the prey themselves. • 4 of 9 mothers were observed eating the prey in 7 of 14 events. • This left 2 of 14 events where it was unconfirmed whether the prey was eaten or not.

22. Discussion • Dolphins can understand human gestures, so why not each other? • Foraging behaviors with calves also appeared more “exaggerated,” like the mothers were trying to make it a game • Some mothers were seen allowing calves to participate in foraging, which supports the teaching hypothesis. They even spent extra energy playing with food to keep calves interested • Conclusion – Teaching evident, TOM remains unproven

23. Alternative Explanations • Brought up by the authors: • Perhaps the latency was brought about by the mother being distracted by her calf • However, foraging without latency was observed when calves were near, but not directly watching • Foraging just for the mother’s nutritional needs? • Alloparenting • The only time the prey was not consumed was when the mothers were foraging with calves, and the calves were unable to catch the prey

24. Our Own Problems • Not enough samples • Cross-generational teaching with only one example • Isolated, highly human-socialized population • Easier sampling, but accurate results? • Are some behaviors adapted for this human-social environment? • Wouldn’t the calves position change the mother’s ability to chase prey?

25. Future Studies • Do mothers teach other calves while alloparenting? • One mother was seen with 2 different calves. • Is teaching limited to foraging behavior? • What other behaviors are culturally transmitted? • Is the same type of teaching behavior seen in captive-raised mothers to captive-raised offspring? Comments?