Background and Overview:

The increase in human population has led to the increase of urban areas, leading many bird species to develop new ways to thrive under these novel conditions. An important fitness technique is how birds respond to fear stimuli. Black-capped chickadees, a common fixture in urban environments due to their non-migratory nature and success in urban parks and woodlands, have developed new behaviors that include altering vocal and nesting behaviors as well as being tolerant of a noisy environment. This makes them a good candidate to study fear response. Anthropogenic impacts like noise, human presence, and novel objects do not appear to have an impact on chickadee fitness. Because of this, researchers hypothesized that fear responses would decrease with the increase in urbanization.

Methods:

24 feeding stations were set up around Kent County, Michigan, which includes suburban and rural areas as well as a mid sized city (Grand Rapids). All 24 stations were at least one kilometer apart and were located in parks owned by the city of Grand Rapids or by the county. Automatic feeders that dispensed seed at peak foraging hours were utilized. As controls, feeders were observed with no additional stimuli and when a familiar object (a branch) was placed at the feeder. The experimental manipulations were: the presence of a cat model, the presence of a novel object, anthropogenic noise, and human approach. Urbanization was quantified by percent of impervious surfaces, distance from the center of Grand Rapids, land cover breakdown, and road length. Each feeder was observed from a hunting blind for seven minutes, then researchers replenished the seed and added either a branch, cat model, or novel object. When testing noise, pink noise was played at steadily increasing increments while observers recorded the number of chickadees present at regular intervals. Human presence was tested by a researching standing increasingly closer to the feeder and recording the number of visits.

Results
Overall, chickadee visits to feeders increased as urbanization increased across the sample sites. Parks that failed to attract chickadees were at the top end of the urbanization gradient. It was found that the branch had no effect on the number of chickadee visits to a feeder, indicating that the presence of an object alone is not enough to deter birds. With nearly all stimuli, chickadee visits to feeders increased with urbanization, except for the introduction of a model cat. When the cat was introduced, chickadee visits did not change with urbanization; rather, they remained about the same across the gradient. Urbanization also led to a decreased fear of noise stimulation. Cats and increased noise are both common effects of urbanization, yet they have opposite impacts on chickadee fear behaviors.

Reflection and Critiques

It seems to me that chickadees are beginning to exhibit less fear response to human-caused effects of urbanization, like noise and the presence of people. I think this is likely because people generally aren’t a threat to chickadees- unlike cats, which are very much a danger. It makes sense to me that heightened fear response towards an increased feline presence would happen in urban areas. I would like to know how realistic the fake cat was, because I’m not sure how much a toy cat really looks like a real cat to birds. This doesn’t seem to have an impact on the study, however. I honestly don’t have a lot to critique; this study was well-planned, very thought out, and did a good job minimizing the impact of any outside variables. My one gripe is that I found the way they graphed the results to be somewhat difficult to follow; it was a very statistical analysis-heavy approach, and I am not exactly a shining example of a statistician. They also only graphed results for two of the experimental variables (cat presence and noise) and I would have liked to see more visualizations of the results. Overall, though, I found this to be an interesting and well-done study.

Van Donselaar, J.L., Atma, J.L., Kruyf, Z.A. et al. Urbanization alters fear behavior in black-capped chickadees. Urban Ecosyst 21, 1043–1051 (2018). https://doi.org/10.1007/s11252-018-0783-5

Background and Overview:

As the amount of urban area increases, habitat fragmentation becomes a bigger and bigger issue for many species. Crayfish are important members of aquatic ecosystems; they serve as a source of food for many other species, they are efficient detritivores, and their tunneling behavior can heavily influence the banks and beds of the streams they live in. They are also suffering from a worldwide decline in population, due primarily to a combination of habitat fragmentation and the introduction of invasive species of crayfish. This study primarily focuses on how culverts in rivers and streams affect two native populations of crayfish in Michigan, Orconectes virilis and Orconectes propinquus and their invasive counterpart, Orconectes rusticus. If O. rusticus is better able to traverse culverts than native crayfish, these barriers would allow O. rusticus to outcompete native species, further contributing to their possible extinction.

Methods:

The area of study for this project was the Carp Lake and Maple River watersheds located in Northern Michigan. Water velocity of 26 culverts at 11 different road crossings was measured and compared to water velocity ~50 meters upstream from the crossing. Velocity was measured 5mm above the stream/culvert bed to accurately reflect conditions that crayfish experience. The only species out of the three that was commonly found near the test culverts was O. propinquus, and its behavior in culverts was measured at three different flow velocities (2, 31, and 42 cm/s). A single crayfish per trial was placed at the starting location and observed for ten minutes or until it moved a meter away. Its location was marked every 30 seconds as well as the number of times the crayfish slipped as it traveled down the culvert. A “slip” refers to an involuntary movement downstream. Each crayfish was only tested once. To compare all three species to one another, a culvert in the Carp River was chosen, and the same process with O. propinquus was repeated with O. virilis, O. rusticus, and O. propinquus. Conditions were altered in the culvert with the creation of a debris dam upstream. To determine the impedance velocity, or the velocity of water at which the crayfish can no longer travel upstream, a flume was constructed in a lab using a propellor and a rubber mat to mimic conditions in a culvert.

Results:

Flow velocity in culverts was significantly higher than flow velocity in the rivers before the culvert. O. propinquus was found to alter its movements at different flow speeds. No crayfish slipped when the flow velocity was 2 cm/s, and more slipped at 42 cm/s than 31 cm/s. Smaller crayfish took longer to complete the trial at higher velocities than larger crayfish did. In order to test the theory that O. rusticus was better able to cross culverts than its native counterparts, all three crayfish species were tested in a culvert to gauge how successful they were at moving 1 meter in 10 minutes. O. rusticus and O. propinquus had fairly similar success rates and trial times, but O. virilis had a significantly harder time traversing the culverts. However, O. rusticus had an average impedance velocity that was several cm/s higher than that of the other two species. In general, larger crayfish had higher impedance velocities than smaller crayfish did.

Reflection and Critiques:

Overall, it seems like culverts will impede certain crayfish more than others, which is true of all types of aquatic animals. While it doesn’t seem like culverts will lead to the extinction of all native crayfish species, it is concerning that there are varieties of crayfish that fair significantly worse in culverts than others. Since crayfish are fairly limited in the ways they can move (by flipping their tail and crawling) they do have a harder time adapting to conditions in culverts than fish might. Most literature focuses around how freshwater fish can move through culverts, so I think that more research into how benthic organisms are affected is important. It is also difficult to say how crayfish from different parts of the US and different water conditions will be affected. I think that future research into crayfish found in different types of streams might be helpful; crayfish found in fast-flowing water might have a better chance at navigating culverts than those in wider, slower streams. One question that I have pertains to the matter of how crayfish are getting into the culverts. The study mentioned that some culverts were elevated above the river, which seems like it would pose an additional obstacle for crayfish. The study also does not account for dry culverts. Ultimately, I think it’s a good study, there are just a few gaps I think need closing.

Foster, H. R., & Keller, T. A. (2011). Flow in culverts as a potential mechanism of stream fragmentation for native and nonindigenous crayfish species. Journal of the North American Benthological Society, 30(4), 1129–1137. https://doi.org/10.1899/10-096.1