semans's blog

Overall, there is a trend of increasing activity with higher temperatures and a decrease in insect activity with decreasing temperature (Fig. 2). We used T-tests to determine whether the experimental means differ significantly from the hypothesized means. In the arena where the temperature was increased, we observed a linear increase in insect activity count from 0 at 10.6°C up to 10 at 21.8°C, persisting at 10 above that temperature (Table 1). Similarly, in the arena where temperature was decreased, we recorded an activity count that decreased from 10 at 26.0°C to 0 at 10.2°C, persisting at 0 under that temperature (Table 1). Figure 2 shows similar trends in activity count for both arenas, with increasing activity being correlated with increasing temperature. This increase in activity is strongly linearly correlated in both groups with an R2 of 0.8874 for the decreasing temperature group and an R2 of 0.8893 for the increasing temperature group (Fig. 2).

The use of electrocommunication to mediate dominance hierarchies and aggressive encounters has been shown in both pulse-type and wave-type fish. Electrocommunication in these contexts has been  related to hormones and even to social history in at least one species, Brachyhypopomus gauderio (Gebhardt et al. 2012, 623; Fugère et al. 2011, 197; Salazar & Stoddard 2009, 399; Cuddy et al. 2012, 4; Raab et al. 2019, 1). Weakly electric fish seem to use different EOD frequencies, EOD lengths, and IDI patterns as competitive indicators for establishing dominance hierarchies and in bouts of ritualised aggression (Gebhardt et al. 2012, 623; Fugère et al. 2011, 197; Salazar & Stoddard 2009, 399; Cuddy et al. 2012, 4; Raab et al. 2019, 1). Research into dominance and aggression has focused largely on wave-type fish (Fugère et al. 2011, 197; Salazar & Stoddard 2009, 399; Cuddy et al. 2012, 4; Raab et al. 2019, 1). In the Sternarchrohynchus genus, EOD frequency has been correlated with body size, and it seems that fish with higher EOD frequencies are dominant over fish with lower EOD frequencies regardless of sex (Fugère et al. 2011, 198). In contrast, the role of EOD frequency in establishing dominance has only been shown in male A. leptorhynchus (Cuddy et al. 2012, 4). Males with higher EOD frequency are dominant and show increased 11-ketotestosterone levels, an important hormone in male electrocommunicative aggression and courtship (Cuddy et al. 2012, 10). However, this study also found that type 2 chirps previously characterised as purely aggressive signals, in fact, do not serve a threatening purpose but may instead signal submission in A. leptorhynchus (Cuddy et al. 2012, 10). It also revealed that type 1 chirps, delineated prior as courtship signals, do not serve this purpose (Cuddy et al. 2012, 10). In holding with this pattern, A. leptorhynchus males with higher EOD frequencies spend more time in habitats that provide good shelter, and are more explorative than males with lower EOD frequencies (Raab et al. 2019, 7). This is likely due to territoriality. Lower EOD males often have to look for new shelter when they lose dominance bouts against higher EOD males which have secured a higher quality territory (Raab et al. 2019, 8).

The paper on song sparrows studies the effects of the transfer function, reverberation, and noise masking of the environment on the trill song of chipping sparrows, with a focus on divergent solutions as a result of intraspecific song variation. A transfer function is a way of describing how the environment filters sound and causes frequency pattern degradation. Urban environments often have transfer functions which favour an intermediate frequency range above low frequency background noise but below frequencies that easily reverberate. Reverberation is a temporal pattern distortion that contributes strongly to impeding signal transmission by adding a tail to notes. As sound waves impact objects they are reflected, which can lead to slurring of both syllable form and pattern. Additionally, due to reverberation, sounds take different paths that can cause both amplitude and frequency interference. The effects of reverb are most pronounced in signals of high frequency, high bandwidth, high duration, and low internote time. In order to compensate for reverberation high obstruction environments such as cities, birds often change their signals by: decreasing minimum frequency, decreasing the number of amplitude and frequency modulations, and increasing internote time. However, in order to transmit their signals above background noise, birds tend to increase the frequency and amplitude of their vocalisations. Although, these modulations can often be hard to separate due to the Lombard effect. Lastly, amplitude and frequency modulated trills are often used by female songbirds as measures of vocal performance, based on how close the male sings to the biophysical limit of the bandwidth to rate ratio. Males which sing closer to this limit are preferred by females and can better defend their territories. In urban environments with highly reflective structures and high background noise, trills suffer heavily from the effects of reverberation and therefore vocal performance is perceived as being poorer. In turn, this has an effect on how well males can both attract females and defend their territories, which means that urban environments could generate unique intra- and intersexual selection pressures.

Drafts

    At the start, the drafts seemed tedious to me, an exercise in producing quantity rather than quality. This feeling persisted throughout the semester and for most of the class I failed to see the point of writing such an abundance of paragraphs. It occurred to me a few times that there was some purpose to the task that yet escaped me. Nevertheless, throughout writing the drafts I never felt that they had any point. Both the act of writing and the product had no meaning to me as the drafts were just reworded fragments of my notes. However, in hindsight it occurs to me that the function of the drafts was just that, to produce quantity and not quality. In having to write so much, I eventually achieved a point where these rough paragraphs simply flowed onto the page and, very unusually, I wasn’t editing my sentences as I was writing them. I now realise that it wasn’t about the content but about the process. Thus, although the act of writing the drafts never seemed to have a point to me, they have fundamentally changed how I write and how I approached this course’s projects. 

Perfect Paragraphs

    At the beginning of the semester, much like the drafts, the perfect paragraphs seemed an exercise in tediousness. Having to edit one of my drafts every week seemed pointless to me, and this feeling remained throughout most of the semester. While I was writing the perfect paragraphs I didn’t feel like I was improving my writing in any way, and the products of my efforts meant nothing to me. I never spent time thinking about the purpose of the perfect paragraphs, they were just another task I had to complete every week. However, upon reflection, I realise that in making the perfect paragraphs I edited my drafts a lot more than I usually edit my writing. Before this class, I used to edit my writing immediately after having finished an assignment. In doing the perfect paragraphs I was often forced to edit my drafts several days later. As such, I was editing my drafts with a fresh perspective that wasn’t as affected by what I was trying to say in my draft but rather by how the message of the draft actually came across to the reader. In sum, even though the purpose of the perfect paragraphs was not immediately obvious to me, they have changed how I edit my writing.

Thusly, only group 1 males showed changes in minimum frequency and bandwidth in response to noise. Neither group 1 nor group 2 males changed their trill rates, which negatively affected their vocal performance. Only the group 1 males showed an increase in minimum frequency because they, unlike the group 2 males, were at risk of having their songs masked by the background noise. Unexpectedly, group 2 males decreased minimum frequency with increasing vegetation, and group 1 males showed higher minimum frequency with increasing urban structure. As noise was not correlated with either urban or vegetative structure, the latter outcome is likely not due to the fact that more structured habitats are noisier. These results suggest that, based on individual variations in their songs, males generate novel spectral adjustments in response to anthropogenic noise. Additionally, peak frequency decreased with increasing urban structure for both groups, likely because lower frequency sounds don’t suffer as much from the effects of reverberation as high frequency sounds. Neither group adjusted their trill rates in response to urban structure, despite the fact that an increase in reflective surfaces causes trill notes to slur. Also, males didn’t shorten their trills in order to minimise accumulation of reverberation over the song. Thus, since group 1 males in an urban setting narrowed their bandwidth but didn’t increase trill rate, they had poorer vocal performance. Similarly, group 2 males in an urban setting suffered poorer vocal performance because they didn’t lower their trill rates,. As such, both groups of males could experience reduced mating success. However, it is possible that males cannot adjust trill rate or song length because of constraints imposed by female preference. Alternatively, males may benefit from sound reflections by picking perches which cause their signals to experience constructive rather than destructive interference. That is, instead of reverberations causing the signals to become slurred and to cancel out, they would add up to increase in amplitude, thereby propagating the signal even further. In sum, it is possible that chipping sparrows in structured environments choose their perches based on how well their song is amplified rather than by how little their song is degraded.

Thusly, only group 1 males showed changes in minimum frequency and bandwidth in response to noise, and neither group 1 nor group 2 males changed their trill rates, which negatively affected their vocal performance. Only the group 1 males showed an increase in minimum frequency because they were at risk of having their songs masked by the background noise unlike the group 2 males who already had minimum frequency above background noise. Unexpectedly, group 2 males decreased minimum frequency with increasing vegetation, and group 1 males showed higher minimum frequency with increasing urban structure. As noise was not correlated with either urban or vegetative structure, the latter outcome is likely not due to the fact that more structured habitats are noisier. These results suggest that, based on individual variations in their songs, males generate novel spectral adjustments in response to anthropogenic noise. Additionally, peak frequency decreased with increasing urban structure for both groups, likely because lower frequency sounds don’t suffer as much from the effects of reverberation as high frequency sounds. Neither group adjusted their trill rates in response to urban structure, despite the fact that an increase in reflective surfaces causes trill notes to be slurred with one another, especially at high trill rates. Males also didn’t shorten their trills in order to minimise accumulation of reverberation over the song. Thus, since group 1 males in an urban setting narrowed their bandwidth but didn’t increase trill rate, they had poorer vocal performance. Similarly, since group 2 males in an urban setting didn’t lower their trill rates, they also suffered poorer vocal performance. As such, both groups of males, and especially group 2 males, could experience reduced mating success. It is possible that males cannot adjust trill rate or song length because of constraints imposed by female preference. Alternatively, males may benefit from sound reflections by picking perches which cause their signals to undergo constructive interference rather than destructive interference. That is, instead of reverberations causing the signals to become slurred and to cancel out, they would add up to increase in amplitude, thereby propagating the signal even further. In sum, it may be the case that chipping sparrows in structured environments choose their perches based on how well their song is amplified rather than by how little their song is degraded. 

This paper was focused on the effects of anthropogenic noise, urban structure, and vegetation on the trills of chipping sparrows. Chipping sparrows evolved in an open habitat, thus an urban environment generates neoteric selection pressures on their song. The researchers aimed to answer three major questions: (1) whether individuals with different song variants generated novel solutions to noise and reverberation; (2) how the opposing forces of background noise and highly reflective structures affect song; and (3) the effects of noise and structures on trills and subsequently, vocal performance. Their predictions hinged on splitting males into two groups. Group 1 was composed of males that had lower minimum frequencies, higher maximum frequencies, broader bandwidths, and lower trill rates than group 2 males. They predicted that group 1 males would sing at a higher and narrower frequency band but would not change their trill rate. Whereas they predicted that group 2 males would decrease trill rate, but wouldn’t change their trill frequency. Lastly, they predicted that noise would have a greater affect on frequency, that structure would have greater affect on song timing, and that vocal performance would decrease with increasing noise and structure.

The paper on song sparrows studies the effect of the environment on the trill song of chipping sparrows, with a focus on divergent solutions to signal deterioration as a result of intraspecific song variation. First and foremost, sounds propagate through the air as waves composed of rarefaction and compaction zones. The density of air particles in the compaction zones is measured as the sound’s amplitude, and the distance between compaction zones is measured as the sound’s frequency. Sounds suffer from two kinds of degradation: frequency -dependent attenuation and reverberation. Attenuation is defined as a decrease in sound intensity with increasing distance. Ideally, sound spreads spherically from the source and intensity decreases in proportion to 1r2, where r is the radius of the sphere. However, environments tend to be heterogeneous, and habitat as well as weather conditions cause excess attenuation on top of the attenuation predicted by spherical spreading. In addition to attenuation, reverberation contributes strongly to impeding signal transmission. As sound waves impact objects they are reflected, which can lead to scattering, slurring of syllable form, and often makes it difficult to distinguish successive elements. These effects are most pronounced in signals of high frequency, high bandwidth, high duration, and low internote time. In order to compensate for attenuation and reverberation in highly obstructed environments such as forests, birds often decrease the minimum frequency and the number of amplitude and frequency modulations of their signals. This type of environmental tuning has been found within single species’ subpopulations living in environments with different levels of obstruction. Therefore, since signals are the primary means by which songbirds compete with one another, for individuals to be able to compete with one other, they must make their signals heard. Commonly, in order to transmit their signals above background noise, birds tend to both increase the amplitude of their vocalisations - known as the Lombard effect - and to sing higher pitched songs. Lastly, amplitude and frequency modulated trills are often used by songbird females as measures of vocal performance, based on how close the male sings to the biophysical limit of the bandwidth to rate ratio. Females prefer males which sing closer to the biophysical limit of trilling and males with stronger trills are better at holding their territories. In urban environments with highly reflective structures and high background noise, trills suffer heavily from the effects of reverberation and therefore vocal performance is perceived as being poorer. In turn, this has an effect on how well males can both attract females and defend their territories, which could mean that urban environments could generate unique intra- and intersexual selection pressures.