Connecting Research Questions

Clara Bird, Masters Student, OSU Department of Fisheries and Wildlife, Geospatial Ecology of Marine Megafauna Lab

The field season can be quite a hectic time of year. Between long days out on the water, trouble-shooting technology issues, organizing/processing the data as it comes in, and keeping up with our other projects/responsibilities, it can be quite overwhelming and exhausting.

But despite all of that, it’s an incredible and exciting time of year. Outside of the field season, we spend most of our time staring at our computers analyzing the data that we spend a relatively short amount of time collecting. When going through that process it can be easy to lose sight of why we do what we do, and to feel disconnected from the species we are studying. Oftentimes the analysis problems we encounter involve more hours of digging through coding discussion boards than learning about the animals themselves. So, as busy as it is, I find that the field season can be pretty inspiring. I have recently been looking through our most recent drone footage of gray whales and feeling renewed excitement for my thesis.

At the moment, my thesis has four central questions: (1) Are there associations between habitat type and gray whale foraging tactic? (2) Is there evidence of individualization? (3) What is the relationship between behavior and body condition? (4) Do we see evidence of learning in the behavior of mom and calf pairs? As I’ve been organizing my thoughts, what’s become quite clear is how interconnected these questions are. So, I thought I’d take this blog to describe the potential relationships.

Let’s start with the first question: are there associations between habitat types and gray whale foraging tactics? This question is central because it relates foraging behavior to habitat, which is ultimately associated with prey. This relationship is the foundation of all other questions involving foraging tactics because food is necessary for the whales to have the energy and nutrients they need to survive. It’s reasonable to think that the whales are flexible and use different foraging tactics to eat different prey that live in different habitats. But, if different prey types have different nutritional value (this is something that Lisa is studying right now; check out the COZI project to learn more), then not all whales may be getting the same nutrients.

The next question relates to the first question but is not necessarily dependent on it. It’s the question of individualization, a topic Lisa also explored in a past blog. Within our Oregon field sites we have documented a variety of gray whale foraging tactics (Torres et al. 2018; Video 1) but we do not know if all gray whales use all the tactics or if different individuals only use certain tactics. While I think it’s unlikely that one whale only uses one tactic all the time, I think we could see an individual use one tactic more often than the others. I reason that there could be two reasons for this pattern. First, it could be a response to resource availability; certain tactics are more efficient than others, this could be because the tactic involves capturing the more nutritious prey or because the behavior is less energetically demanding. Second, foraging tactics are socially learned as calves from their mothers, and hence individuals use those learned tactics more frequently. This pattern of maternally inherited foraging tactics has been documented in other marine mammals (Mann and Sargeant 2009; Estes et al. 2003). These questions between foraging tactic, habitat and individualization also tie into the remaining two questions.

My third question is about the relationship between behavior and body condition. As I’ve discussed in a previous blog, I am interested in assessing the relative energetic costs and benefits of the different foraging tactics. Is one foraging tactic more cost-effective than another (less energy out per energy in)? Ever since our lab’s cetacean behavioral ecology class, I’ve been thinking about how my work relates to niche partitioning theory (Pianka 1974).This theory states that when there is low prey availability, niche partitioning will increase. Niche partitioning can occur across several different dimensions: for instance, prey type, foraging location, and time of day when active. If gray whales partition across the prey type dimension, then different whales would feed on different kinds of prey. If whales partition resources across the foraging location dimension, individuals would feed in different areas. Lastly, if whales partition resources across the time axis, individuals would feed at different times of day. Using different foraging tactics to feed on different prey would be an example of partitioning across the prey type dimension. If there is a more preferable prey type, then maybe in years of high prey availability, we would see most of the gray whales using the same tactics to feed on the same prey type. However, in years of low prey availability we might expect to see a greater variety of foraging tactics being used. The question then becomes, does any whale end up using the less beneficial foraging tactic? If so, which whales use the less beneficial tactic? Do the same individuals always switch to the less beneficial tactic? Is there a common characteristic among the individuals that switched, like sex, age, size, or reproductive status? Lemos et al. (2020) hypothesized that the decline in body condition observed from 2016 to 2017 might be a carryover effect from low prey availability in 2016. Could it be that the whales that use the less beneficial tactic exhibit poor body condition the following year?

My fourth, and final, question asks if foraging tactics are passed down from moms to their calves. We have some footage of a mom foraging with her calf nearby, and occasionally it looks like the calf could be copying its mother. Reviewing this footage spiked my interest in seeing if there are similarities between the behavior tactics used by moms and those used by their calves after they have been weaned. While this question clearly relates to the question of individualization, it is also related to body condition: what if the foraging tactics used by the mom is influenced by her body condition at the time?

I hope to answer some of these fascinating questions using the data we have collected during our long field days over the past 6 years. In all likelihood, the story that comes together during my thesis research will be different from what I envision now and will likely lead to more questions. That being said, I’m excited to see how the story unfolds and I look forward to sharing the evolving ideas and plot lines with all of you.

References

Estes, J A, M L Riedman, M M Staedler, M T Tinker, and B E Lyon. 2003. “Individual Variation in Prey Selection by Sea Otters: Patterns, Causes and Implications.” Source: Journal of Animal Ecology. Vol. 72.

Mann, Janet, and Brooke Sargeant. 2009. “ Like Mother, like Calf: The Ontogeny of Foraging Traditions in Wild Indian Ocean Bottlenose Dolphins ( Tursiops Sp.) .” In The Biology of Traditions, 236–66. Cambridge University Press. https://doi.org/10.1017/cbo9780511584022.010.

Pianka, Eric R. 1974. “Niche Overlap and Diffuse Competition” 71 (5): 2141–45.

Soledade Lemos, Leila, Jonathan D Burnett, Todd E Chandler, James L Sumich, and Leigh G. Torres. 2020. “Intra‐ and Inter‐annual Variation in Gray Whale Body Condition on a Foraging Ground.” Ecosphere 11 (4). https://doi.org/10.1002/ecs2.3094.

Torres, Leigh G., Sharon L. Nieukirk, Leila Lemos, and Todd E. Chandler. 2018. “Drone up! Quantifying Whale Behavior from a New Perspective Improves Observational Capacity.” Frontiers in Marine Science 5 (SEP). https://doi.org/10.3389/fmars.2018.00319.

Who Am I? Exploring the theory of individualisation among marine mammals

By Lisa Hildebrand, MSc student, OSU Department of Fisheries and Wildlife, Geospatial Ecology of Marine Megafauna Lab

“Just be yourself!” is a phrase that everyone has probably heard at least once in their lives. The idea of being an individual who is distinctly different from other individuals is a concept that is focal to the society we live in today. While historically it may have been frowned upon to be the “black sheep in the crowd”, nowadays that seems to be the goal.

Source: Go Comics.

This quest for uniqueness has resulted in different styles of fashion, speech, profession, interest in art, music, literature, automobile types – the list is endless. The American Psychological Association defines personality as the “individual differences in characteristic patterns of thinking, feeling and behaving”1. So, all of the choices we make on a daily basis shape our behaviour, and our behaviour in turn shapes our personality.

Since personality is something that is so engrained within human society, it isn’t surprising that ecologists have explored this concept among non-humans. Decades of research have resulted in an abundance of literature detailing personality in many different taxa and species, ranging from chimpanzees to mice to ants2. Naturally, the definition of personality for animals differs from that for humans since the assessment of animal thoughts and feelings is still somewhat of a locked box to us. Nevertheless, the behavioural aspect of the two definitions remains consistent whereby animal personality is broadly defined as “consistent variation in behavioural traits between individuals”3.

Although I am an early career marine mammal ecologist finding my footing in this rapidly expanding field, I have a keen interest in teasing apart possible cases of individual specialisation within marine mammal populations. So, before getting straight into the nitty gritty of individual specialisation, it is important for me to take a small step back and consider the concept of specialisation as applied to small subgroups or populations of marine mammals.

Specialisations are mostly related to foraging or feeding behaviour whereby a subgroup of individuals will develop a novel method to locate and capture prey. These behaviours have been reported for several marine mammal species, and are strongly coupled to intra and inter-specific competition with other predators for prey and habitat characteristics. Furthermore, it is posited that factors such as resource benefits (e.g. energy content of prey), prey escape rates, and handling times can be minimised if specialisation for a particular prey type or habitat occurs4.

In Florida Bay, Torres & Readdocumented two distinct foraging strategies employed by two bottlenose dolphin ecotypes. One dolphin ecotype was found to forage using deep diving with erratic surfacings, whereas the second ecotype chose to forage through mud ring feeding and were mostly seen in shallow habitats. The latter ecotype is in fact so adapted to shallow depths that dolphins were typically observed foraging in waters <2 m deep. In this example, the foraging tactics of the two ecotypes are strongly driven by habitat conditions, specifically depth. The video below is aerial footage of bottlenose dolphins performing mud ring feeding.

Such group specialisations have been identified not only in several other bottlenose dolphin populations around the world6,7, but also in other cetacean species, including killer whales (distinct differences in target prey between transients and residents8), Guiana dolphins (mud-plume feeding9), humpback dolphins (strand feeding10), and several others. Noticeable here is that these records concern Odontocete species, which is not surprising since these toothed whales are vastly different to baleen whales in that they often live in structured groups with bonds between individuals sometimes lasting for decades11. Long-term relationships are conducive to developing specialised group hunting strategies as individuals will spend considerable time with one another and the success of obtaining prey depends on the cooperation and coordination of the group.

For baleen whales and other marine mammals, such as pinnipeds, where life history and social organisation is more geared toward a solitary life, examples of group specialisations are relatively rare (with the exception of the well-documented bubble-net feeding exhibited by humpback whales12). While group specialisation may not be as prevalent in Mysticetes, the same problems of inter and intra-specific competition persists among these more solitary species too, which would suggest that individuals should develop their own unique foraging tactics and preferences. Evidence for individualisation is hard to obtain since it requires repeated observations of the same individuals over time with good knowledge of the prey type being consumed and/or the habitat being used to forage in.

Nevertheless, examples do exist. Perhaps the most well-documented case of individualisation within a population for marine mammals is of the sea otter. Estes et al. (2003) describe 10 female sea otters in Monterey Bay that had high inter-individual variation in diet, which they investigated over a scale of 8 years13. Most females specialised on 1-4 types of prey, with marked differences between the diets chosen by each female, despite habitat overlap. This individualisation of diet was not attributable to variation in prey availability; hence, authors concluded that this extreme specialisation occurred to reduce intra-population competition for prey.

Ecologists have historically (and probably still to this day) disagreed on whether individualisation actually matters in the grand scheme of things. There are generally three schools of thought on the matter: (1) individual specialisation is rare and/or weakly influences population dynamics and so is not very important; (2) while individual specialisation does occur and may in fact be commonplace, it does not affect ecological processes at the large population scale; and (3) individual specialisation is widespread and can significantly impact population dynamics and/or ecosystem function.

As you might have guessed by this point, I find myself in the third school of thought. There are many arguments supporting this theory, and what I believe to be very good arguments against statements 1 and 2. While I have only provided one specific named example for individual specialisation in a marine mammal, there are several documented cases of such occurrences among other marine taxa (e.g., pinnipeds14, sharks15, fish16) and a much larger number of studies for terrestrial species4. Thus, the claim that it is rare or weak, seems implausible to me.

Statement 2 is a little more complicated to tackle as it involves understanding how actions on a relatively small scale affect a whole population or even an ecosystem. For instance, consider two female sea otters living in a small coastal area where one sea otter prefers to eat turban snails and the other exclusively feeds on abalone. The sudden decline in abundance of either of these prey could lead to serious health and reproductive issues for those females. Should the low prey abundance persist, then poor health and reproduction of several females in a population that specialise on that prey item can rapidly lead to genetic loss and an overall population decline. Particularly if an individual’s or species’ home range is rather restricted or small. In the case of the sea otter, which are often touted as a keystone species due to its presence preventing sea urchin barren formation that is known to wreak havoc on kelp forests, knock-on effects of such a population decline could result in poor overall ecosystem health.

It may be easy to assume that one individual dolphin, otter, seal or whale cannot possibly make a difference to a whole population or ecosystem. This assumption strikes me as a little odd since humans are always told to ‘be the change they wish to see in the world’ and that ‘every person can make a difference’. Why then should these sentiments not be applicable to non-humans? While a gray whale may not hold a sign at a protest or run for president (actions commonly considered to cause change in the human world), perhaps the choice that a gray whale makes every day to only consume one species of zooplankton, can influence other gray whales in the area, predators from other taxa, habitat structure, other prey availability, and/or cause trophic cascades.

Through my research, I aim to elucidate whether the gray whales display some level of foraging individualisation while feeding in Port Orford, Oregon. I will use data from four years to compare tracks of individual whales with zooplankton samples collected in the area to correlate each individual’s movement patterns with prey availability. I will assess the quality of prey through bomb calorimetry and microplastic analysis of the zooplankton samples to determine energetic content and pollutant levels, respectively. This prey assessment will describe the potential effects of prey specialization on whales, which is fundamental to assessing overall population health. Individualisation can strongly affect fitness of individuals, either positively or negatively depending on several factors, which will undoubtedly have an impact at the population level.

(The videos below are examples of two different tactics we see the gray whales display while foraging along the Oregon coast in the summer months. The first video shows a whale foraging among kelp with some very acrobatic moves, while the second is of a whale employing the ‘sharking’ method where the whale is feeding benthically in such shallow depths that both the pectoral fin and the fluke stick out of the water, making the whale look like a ‘shark’.)

References

  1. American Psychological Association, Personality. Retrieved from: https://www.apa.org/topics/personality/.
  2. Carere C., & Locurto, C., Interaction between animal personality and animal cognition. Current Zoology, 2015. 57(4): 491-498.
  3. Gosling, S.D., From mice to men: what can we learn about personality from animal research?Psychological Bulletin, 2001. 127(1): 45-86.
  4. Bolnick, D.I., et al., The ecology of individuals: incidence and implications of individual specialisation. The American Naturalist, 2003. 161(1): 1-28.
  5. Torres, L.G., & Read, A. J., Where to catch a fish? The influence of foraging tactics on the ecology of bottlenose dolphins (Tursiops truncatus) in Florida Bay, Florida. Marine Mammal Science, 2009. 25(4): 797-815.
  6. Gisburne, T.J., & Connor, R.C., Group size and feeding success in strand-feeding bottlenose dolphins (Tursiops truncatus) in Bull Creek, South Carolina. Marine Mammal Science, 2015. 31(3): 1252-1257.
  7. Gazda, S.K., et al., A division of labour with role specialization in group-hunting bottlenose dolphins (Tursiops truncatus) off Cedar Keys, Florida.Proceedings of the Royal Society: Biological Sciences, 2005. 272(1559): 135-140.
  8. Ford, J.K.B., et al., Dietary specialization in two sympatric populations of killer whales (Orcinus orca) in coastal British Columbia and adjacent waters. Canadian Journal of Zoology, 1998. 76(8): 1456-1471.
  9. Rossi-Santos, M.R., & Wedekin, L.L., Evidence of bottom contact behaviour by estuarine dolphins (Sotalia guianensis) on the Eastern Coast of Brazil.Aquatic Mammals, 2006. 32(2): 140-144.
  10. Peddemors, V.M., & Thompson, G., Beaching behaviour during shallow water feeding by humpback dolphins (Sousa plumbea). Aquatic Mammals, 1994. 20(2): 65-67.
  11. Tyack, P., Population biology, social behavior and communication in whales and dolphins. Trends in Ecology & Evolution, 1986. 1(6): 144-150.
  12. Wiley, D., et al., Underwater components of humpback whale bubble-net feeding behaviour.Behaviour, 2011. 148(5/6): 575-602.
  13. Estes, J.A., et al., Individual variation in prey selection by sea otters: patterns, causes and implications. Journal of Animal Ecology, 2003. 72(1): 144-155.
  14. Cherel, Y., et al., Stable isotopes document seasonal changes in trophic niches and winter foraging individual specialization in diving predators from the Southern Ocean. Journal of Animal Ecology, 2007. 76(4): 826-836.
  15. Matich, P., et al., Contrasting patterns of individual specialization and trophic coupling in two marine apex predators. Journal of Animal Ecology, 2010. 80(1): 294-305.
  16. Svanbäck, R., & Persson, L., Individual diet specialization, niche width and population dynamics: implications for trophic polymorphisms. Journal of Animal Ecology, 2004. 73(5): 973-982.