I’ve talked a lot about monkey minds on this blog, but it’s about time I got to the bird brains. Birds may have a reputation for being stupid (hence the disparaging term “birdbrain”), but they actually have some pretty incredible cognitive abilities. In fact, pigeons are one of the most widely studied animals in animal cognition labs.
This week, though, I’m going to discuss a study that looks at cognition in a different bird, the North Island Robin of New Zealand, and in their natural habitat rather than in a lab. In this study, Barnett et al. (2013) investigated whether these birds could discriminate between familiar and novel humans.
Research has shown that birds can recognize humans who have previously approached their nests or captured them for tagging, which makes evolutionary sense: being able to recognize predators allows the birds to respond appropriately (e.g. fly away), increasing their chances for survival.
In this experiment, though, the researchers were not acting like a threat; instead of approaching the bird, a researcher placed a mealworm on the ground, then stood one meter away and timed how long it took for the bird to eat the mealworm. This encounter is likely much less stressful to the bird than if the researcher approached the bird’s nest or tried to capture it. This could actually affect the bird’s memory of the researcher because of something called the corticosterone response. When a non-human animal is stressed, its body releases corticosterone (cortisol is the human equivalent). One effect of corticosterone is to improve the formation of memories, so birds may be more likely to recognize a familiar human they’ve previously encountered in a stressful situation than one encountered in a less stressful or neutral situation.
In order to test whether the robins could discriminate between familiar and novel humans, Barnett et al. used a habituation task: they repeated the above procedure (timing how long it took for a robin to eat the mealworm) once a day for 7 days, always with the same researcher. On the 8th day, they used a different researcher.
Animals tend to be cautious when exploring novel things, so the researchers expected that the robins would be slower to eat the mealworms on the first few days. Eventually, though, they would habituate to the researcher and their “attack latency” (how long it took to eat the mealworm) would decrease. The critical data, then, is the robins’ attack latencies on the 8th day, with the new researcher. Longer attack latencies on Day 8 compared to Day 7 would indicate that the robins perceive the researcher as novel, showing that the robins can discriminate between familiar and novel humans. However, no change in attack latency on Day 8 would suggest that the robins cannot discriminate between familiar and novel humans.
But Barnett et al. were interested in more than the overall discriminative ability of North Island Robins; they also wanted to see how individual differences in behavior from bird to bird were related to this discriminative ability. Animals, like humans (although probably to a lesser extent), exhibit variations in behaviors and responses on an individual basis. The human equivalent of this is personality, although researchers also refer to it as temperament. This topic is somewhat controversial, but there are two generally accepted requirements for a behavioral trait to be considered a personality trait. First, the trait must be stable and consistent (not just a one-time behavior). Second, that trait must be related to other traits. For example, boldness, a personality trait indicating risk-taking tendency, is also related to exploratory behavior and aggressiveness.
Previous research indicates that differences in personality traits are associated with differences in learning and interacting with the environment, which is why Barnett et al. wanted to investigate individual behavioral differences in the robins. Based on the attack latency data from Day 4 (when all the animals had habituated) to Day 7, the researchers split the robins into two “behavioral types”: fast attackers and slow attackers.
The researchers found that the fast attackers did not have an increased attack latency on Day 8, suggesting that they could not discriminate between the familiar and novel researcher (or that they could discriminate between them, but didn’t perceive the novel researcher as threatening). The slow attackers, on the other hand, did have an increased attack latency on Day 8, showing that they could discriminate between the researchers. Moreover, when Barnett et al. compared the attack latencies between the two groups over all 8 days (not just Day 4 through Day 8), they found that the fast attackers habituated to the researcher on the second day, while the slow attackers didn’t habituate until the fourth day. This result agrees with previous findings that bolder animals are quicker to explore novel environments and form routines.
Barnett et al. offer a couple hypotheses of mechanisms behind these behavioral differences. Perhaps the slow learners paid more attention to their environment during the habituation phase (Days 1-7), allowing them to better perceive when the researcher was different. Another theory is that the slow attackers may have a greater corticosterone response than the fast attackers. This could cause the slow attackers to have a much better memory for the familiar researcher.
In addition to showing that North Island Robins can discriminate between familiar and novel humans, this study demonstrates that personality traits can affect individual animals’ behavioral responses. It also suggests that animal cognition researchers should take into account the personality traits of individuals when conducting cognition experiments.
Barnett, Craig, et al. “The ability of North Island robins to discriminate between humans is related to their behavioural type.” PloS one 8.5 (2013): e64487.