Dovid Kovlovsky is a PhD student at the University of Nevada, Reno. Here he shares the experience of conducting a recent experiment with mountain chickadees in the Sierra Nevada mountains. Article written by Dovid Kovlovsky, edited by Felicity Muth.
Slinking through the forest, tripod on my shoulder, binoculars and stopwatch around my neck, I am ready to conduct science. The tripod, however, does not belong to a camera, instead it belongs to a stuffed dead hawk model. You see, I wanted to ask an age-old question: when life is rough would your parents put you at risk to save themselves? To answer this question, we enter the eastern Sierra Nevada in search of the not so rare nor elusive Mountain Chickadee. Our field site is composed of an expanse of tall coniferous trees, manzanita and small shrubs with pine needles and pine cones blanketing the ground. During the spring and summer, dirt flies everywhere, the sun tries to fry everything and water is a precious commodity, while the late fall and winter bring heavy snowpacks and cold temperatures. While many animals call this forest their home during the spring, a few species stick around to weather the brutal winters. Regardless of the season, no animal is more abundant than our angry and aggressive little friend, the mountain chickadee.
Mountain chickadees are residents that live across a range of elevations, meaning that some chickadees that live higher up have to deal with more extreme winter climate. Being higher up also means that these birds have a short breeding season, and we all know how important breeding is. Not incubating (warming the eggs), or not feeding nestlings for extended periods of time can have dire and irreparable consequences for a young bird (-to-be). Having a shorter breeding season means these birds might behave a certain way. For example, a short breeding season means there is no time to try again if things fail, so these birds contending with a short season might try harder on the first attempt, putting all their eggs in one basket. If you only live a short life and you only get to breed for a very small window of time, you breed your little chickadee heart out even if you are worried about being eaten by a hawk. However, if you live the good life, where you get to breed for longer, perhaps you are less willing to give your life to breed when future opportunities may present themselves. At least that was my reasoning.
To find out whether chickadees that live high up behave differently in response to predators, I carried out an experiment. To do this, I placed a tripod at the entrance to a nestbox and scrambled away to become one with a distant pine tree, while keeping my binoculars trained on the recently departed female and the nest. When the female returned, what did she do? The mother stopped short of the nest area, rather than ‘bird’-lining it straight for the entrance. She was agitatedly hopping from branch to branch scolding the hawk for being near her nest. She flew off, only to return later. Eventually, she entered the box to make her eggs hot.
I grinned ecstatically as I struggled to breathe from running to the nest to remove the hawk: my first hawk presentation was a resounding success. On other trials, I was not so fortunate. My ethereal enemy, the wind, had other plans for my experiment.
It was a calm, slightly overcast day and the hawk was in place. While I patiently watched the nest tree, I let out a string of expletives as huge gusts of wind topple the tripod. The trial was a bust and so I retired to the truck. The following day at the peak of the mountain the winds were fierce. Ensuring that the tripod was firmly in place, I once again scurried to my watching tree. Throughout the trial I wondered how much more of a battering the hawk could take. I didn’t need to wonder much longer: soon after that a few intense gusts of wind nearly took the birds’ wing off.
After patching up the hawk mount I continued my experiment, but I also wanted to know how both parents responded to a predator after having invested even more in their offspring. Since both parents feed their chicks, I conducted similar trials once the chicks had hatched and the parents were feeding them as nestlings. I found that both when parents were incubating, and when they were feeding their nestlings, they were hesitant to enter their nests in the presence of these ‘hawks’. However, the parents responded differently depending on how far up the mountain they lived. If they were from high elevation, the parents were much more likely to be scared away by the ‘hawk’ predator.
What does this mean for parents during rough times? At least in mountain chickadees, those parents that contend with a harsher environment will be more likely to cause harm to their children than risk themselves. You may recall (or you may not) that I predicted the opposite would happen.
How might these unexpected results be explained? One possibility comes from a study on a closely-related English bird called the Great Tit (leave it to old English men). Ella Cole and her colleagues found that parents who were better at solving a novel problem were also more likely to abandon their offspring when disturbed. High elevation chickadees, like their problem-solving cousins, have superior cognition compared to their less smart low elevation counterparts. Mountain Chickadees use food-storing as a way to survive winter. Since high elevation chickadees contend with harsher environments, they have superior spatial memory than low elevation chickadees, allowing them to recover enough stores to survive more severe winters. So, could it be that there is some kind of trade-off between being smart and being willing to take a risk? The reason behind these results remains intangible, but maybe smart individuals just make poor parents.
Kozlovsky DY, Branch CL, Pravosudov VV. 2015. Elevation-related differences in parental risk-taking behavior are associated with cognitive variation in mountain chickadees. Ethology 120: 1-12.
Cole EF, Morand-Ferron J, Hinks AE, Quinn JL. 2012. Cognitive ability influences reproductive life history variation in the wild. Current Biology 22: 1808—1812.