Abstract
Introduction:
The escalating mental health crisis among college students presents a global challenge that may be exacerbated by isolation from nature. Previous research, largely conducted in laboratory settings, indicates that exposure to nature and birdsong improves mental and physiological health. We built on this work with an outdoor experiment testing for independent and potentially additive effects on physiological stress associated with exposure to natural landscapes (i.e., forests) and soundscapes (i.e., birdsong).
Methods:
We engaged 95 participants from North Carolina State University in a randomized, four-treatment, within-subjects design to evaluate the effects of adding different sounds (birdsong vs. traffic) to landscapes (forest vs. gray space) on measures of physiological stress: heart rate (HR) and heart rate variability (HRV) (measured as RMSSD). We started each sample with 5 min of silent control, followed by 10 min of recorded birdsong or recorded traffic noise. Participants listened to each recording in both settings. We modeled HR and HRV using linear mixed models with a random intercept to account for participant effects and fixed effects for soundscape, landscape, their interaction, age, and gender.
Results:
Forest exposure had reduced HR relative to gray space (b = 0.65, p = 0.007). Birdsong exposure increased HRV relative to traffic noise (b = -1.38, p = 0.049). We did not detect a significant soundscape × landscape interaction for either outcome (all p > 0.16).
Discussion:
These findings indicate that visual and auditory nature cues may support physiological recovery through partially independent pathways, with forest landscapes associated with reduced cardiovascular arousal and birdsong soundscapes associated with increased autonomic recovery. Results highlight the different ways that green infrastructure on college campuses can improve students’ mental health outcomes.
Introduction
Nature-dependent activities (e.g., hiking in forests) have a positive influence on mental health, including reducing stress, improving emotional health, and improving sleep quality (Stigsdotter et al., 2010; Tillmann et al., 2018; ; White et al., 2019). The effects of time in nature may be particularly strong among youth, for whom mental health challenges are pervasive and are becoming more common (Plana-Ripoll et al., 2022; McGorry et al., 2025). For example, approximately 60% of college students reported mental health challenges in 2020 (). This crisis continued after 2020, with notable declines in mental health throughout the COVID-19 pandemic for most demographic groups (; ), including college students (; ). Nature-based activities, however, may have prevented greater declines in mental health during this time (), particularly among youth (; ). Despite the value of nature as a preventative health promotion pathway (; ), fewer people are spending time outside. According to , Americans spend 87% of their time in enclosed buildings. A national report on the Nature of Americans (2017) reported that, although people enjoy nature, their time spent outdoors has declined further in recent decades. This disconnection with nature may lead to profound health consequences.
The stress-reducing effects of exposure to nature may operate through multiple sensory pathways (). Stress reduction theory (SRT; Ulrich et al., 1991) suggests that an unthreatening natural environment evokes positive emotions, physiological recovery, and relaxation because humans have a genetically ingrained affinity for settings in which they evolved. Research in laboratory settings has isolated visual (Shi et al., 2024) and auditory (; Yoon and Jeon, 2025) pathways for well-being benefits associated with nature exposure. These studies often highlight the value of natural sights and sounds relative to anthropogenic ones, such as traffic noise and urban skylines (; ). Vegetation, water features (; Shi et al., 2024), and landscape structure (e.g., slope, and scale; ) have been associated with lower physiological stress and improved mental health outcomes. In contrast, anthropogenic sounds, particularly traffic noise, have historically been associated with heightened stress and annoyance () and negative health outcomes (Osborne et al., 2020). Studies have also discovered an olfactory pathway that links contact with nature to human well-being (). Collectively, these studies show that multi-sensory contact with nature can both restore capacities and reduce harm, leading to positive impacts on mental health ().
Birdwatching represents one nature-based activity with a notable auditory element (birdsong) that may impact well-being (; Zielonka et al., 2024; ). Although birdwatching has visual elements, growing evidence indicates that birdsong itself plays a vital role in shaping the restorative value of time in nature (). In most research, restorativeness refers to the degree to which an experience aids recovery from stress, renews cognitive function, and promotes emotional recovery (Randler et al., 2023; Ratcliffe et al., 2016, 2018). Hartig and others have highlighted the uniquely restorative qualities of natural environments (). Lab-based research indicates birdsong can reduce stress, anxiety, and paranoia, and may promote restorativeness (; Stobbe et al., 2022). conducted a hybrid study demonstrating a correlation between greater birdsong diversity provided by speakers installed on hiking trails and increased restorativeness among hikers. Peterson et al. (2024) found that birding while walking on a college campus can reduce psychological distress and support well-being. Some studies, however, have not detected health benefits from birdwatching (Ratcliffe et al., 2013; ; Yi et al., 2024). These mixed results may be explained in multiple ways. First, physiological and self-reported responses to nature exposure do not always align, and self-reported assessments of well-being impacts are often larger than those detected using physiological measures (Scott et al., 2020). Second, a lack of congruence between sensory inputs (e.g., hearing running water where there is no water) may complicate the effects of nature exposure. For instance, urban sounds in undeveloped greenspace may create disturbing dissonance and reduce the therapeutic value of the experience (Van Renterghem and Lippens, 2024; ).
In this study, we built on previous literature by conducting a 2 × 2 within-subjects experiment to assess the degree to which natural and anthropogenic soundscapes (birdsong and traffic) affected physiological measures of stress (heart rate (HR) and heart rate variability (HRV)) in two landscapes (a forest and an urban gray space). We hypothesized that the forest and birdsong treatment would reduce physiological stress relative to gray space and traffic sounds. Similarly, we hypothesized that better-matched auditory and visual environments (e.g., birdsong in the forest) would reduce stress relative to poorly-matched auditory and visual environments (e.g., birdsong in the gray space). The first hypothesis is predicted by SRT, given that forest landscape and birdsong best emulate the nonthreatening landscapes that historically signaled safety and resource availability to humans (Ulrich et al., 1991). The second hypothesis is predicted by frameworks of cross-modal congruence and consistency, which suggest that mismatches between auditory and visual environmental cues place greater demands on the semantic working memory system, increasing cognitive load, reducing processing power, and ultimately diminishing physiological and psychological benefits (Olivetti Belardinelli et al., 2004, Van Renterghem and Lippens, 2024).
Methods
We implemented a 2 × 2 within-subjects design crossing location (forest vs. gray space) with soundscape (birdsong vs. traffic noise) to assess treatment effects on HR and HRV (Heart rate variability). Heart rate data was collected using a Polar H10 heart-rate band paired with a personal cell phone. Higher HR is often associated with greater stress (). We measured HRV using the Root Mean Square of Successive Differences (RMSSD), a time-domain measure of heart rate variability that calculates beat-to-beat variance in heart rate that is driven by the parasympathetic nervous system, with higher variance indicating lower stress (; Shaffer et al., 2014). Thus, larger increases in HRV indicate the treatment reduced stress, and decreases in HRV indicate the treatment increased stress. The experiment was conducted on the grounds of North Carolina State University in Raleigh, North Carolina, USA. We used the dot-grid method to measure tree canopy and built structure coverage at the two landscape treatment locations (). The forest site was located within the footprint of the Rocky Branch Stream Restoration and Greenway Project (), a restoration completed in 2006. At the time of data collection, the area surrounding the participant seating location (>50-m radius buffer) consisted of more than 70% closed forest canopy and less than 30% built infrastructure (e.g., buildings, paved paths, parking areas). Importantly, participants had no direct forward-facing views of anthropogenic structures (Figure 1). Geographic coordinates for the restored forest site are 35.780246, −78.668538. The gray space treatment was located outside Talley Student Union, a building on the campus of North Carolina State University. Within a 50-m buffer of the seating location, built structures covered more than 70% of the area, whereas forest canopy covered less than 30%. In contrast to the forest site, this location included direct sight lines to surrounding buildings and infrastructure (Figure 1). Geographic coordinates for the gray space landscape are 35.783181, -78.670695. Each soundscape treatment consisted of a 5-minute track of silence, followed by a 10-minute track of either birdsong or traffic (Figure 2). The birdsong soundscape was recorded at a freshwater marsh in the St. Marks National Wildlife Refuge, Florida, USA, in the afternoon on 17 May 2023 (Singer, 2023). The recording was dominated by blue-gray gnatcatchers (Polioptila caerulea), Carolina wrens (Thryothorus ludovicianus), and white-eyed vireos (Vireo griseus), and included red-bellied woodpeckers (Melanerpes carolinus), belted kingfishers (Megaceryle alcyon), mourning doves (Zenaida macroura), and gray catbirds (Dumetella carolinensis; all common species in our study site (Peterson, 2020). The traffic noise soundscape was recorded at a high-traffic intersection in Créteil, France, within the greater Paris metropolitan region, on 12 November 2020 (Moulaythami, 2020). Both sound files are provided in the Supplementary Materials. Participants were instructed to start with VLC volume at 50%, which is between 50 and 70 dB for most devices, and not to change volume between treatments. We did not measure sound pressure levels at the headphones of participants due to logistical constraints, so they likely varied between participants but not between treatments for a single participant.
Figure 1
Figure 2
Participants were recruited from students in classes offered by the NC State University College of Natural Resources (n = 107). One week prior to data collection, participants received an email thanking them for participating and outlining participation instructions. Each email contained individualized instructions specifying a randomly assigned, but blocked order of location and soundscape treatments. Participants were randomly assigned a starting location (forest or grey-space landscape, Figure 1). From that starting location, the order of the soundtracks was randomized so that either birdsong or traffic noise was presented first, but the location would not change until both soundscapes were heard. In the second location, the soundscapes were randomized in the same way. Participants were able to complete treatments on any day between February 7th and April 22nd, 2025, as long as there was no precipitation and the temperature was between 20 and 25 degrees Celsius, a range at which temperature has minimal impact on stress (Seppänen and Fisk, 2006). During the treatment, participants sat in a camp chair with armrests and listened to the assigned track through over-the-ear noise-canceling headphones. Once both treatments were completed at the first location, participants then walked to their second assigned landscape and repeated the procedure in their randomly assigned order. Completion of all four treatments took approximately two hours. Total time, including planning and completion of all four treatments, took approximately three hours.
Raw output files from the Elite HRV app () were processed in Kubios Scientific Version 4.1.2.1 using a beat-correction threshold of “low”, which allows detected artifacts to be replaced using cubic spline interpolation on the RR interval axis (Tarvainen et al., 2014). The HRV data were then segmented into a control period (0-5:00 minutes) and a treatment period (5:01-15:00 minutes). To minimize transitional noise and ensure no overlap between control and treatment data, we removed the first minute of the control period (0:00-1:00), 1 minute equally spanning the end of the control period and beginning of the treatment period (4:30-5:30 of the original recording), and the last minute of the treatment period (14:00-15:00 of the original recording). This eliminated data that may have been collected during transitions between procedures and helped ensure that each analyzed segment represented steady-state conditions. This trimming resulted in a standardized 12-minute period, broken into a 3:30-minute control period and an 8:30-minute treatment period.
We used linear mixed-effects models (LMMs) to examine treatment effects on HR and HRV and included a random effect for each participant to account for the repeated-measures design. Each model included fixed effects for soundscape (birdsong vs. traffic), landscape (forest vs. gray space), their interaction, gender, and age. Formulas for the linear mixed models were as follows:
Modeling was conducted via JMP Student Edition 19, with restricted maximum likelihood estimation, unbounded variance components, and a compound symmetry error structure. Due to the small numbers of non-binary (n = 3) and prefer not to say (n = 1) respondents, gender was dichotomized into male and non-male to simplify our model. We modeled treatment-period absolute values of HR and HRV rather than change scores (treatment minus control) because the visual landscape was consistent during both the control and treatment periods for a given location, meaning the tonic effect of landscape was already present in both control and treatment and therefore neutralized (i.e., canceled out in difference scores). We fit equivalent LMMs to predict the control-period HR and HRV values. Before analysis, we removed 12 participants due to incomplete data, leaving a total number of 95 participants for analysis.
Results
We worked with 95 participants, a majority of whom self-identified as female (56.4% female, 37.0% male, 5.5% non-binary, 1.1% prefer not to say). The mean age of participants was 22.51 (SD ± 3.71) years. The mean outside temperature at treatment completion was 21.22 degrees Celsius (SD ± 8.73; 70.20 degrees Fahrenheit). During the control period, HRV was not impacted by soundscape (b = -0.72, SE = 0.83, p = .388), landscape (b = -1.26, SE = 0.83, p = .130), or their interaction (b = -1.15, SE = 0.83, p = .168; Table 1), consistent with baseline comparability across the four treatments. During the control period, however, average HR was higher in gray space than in the forest landscape (b = 0.83, SE = 0.29, p = .005). Neither soundscape (b = 0.26, SE = 0.29, p = .378) nor the interaction between landscape and soundscape predicted control period HR (b = 0.24, SE = 0.29, p = .394).
Table 1
| Variables | Heart rate | Heart rate variability | ||||
|---|---|---|---|---|---|---|
| B | SE | P | B | SE | P | |
| Soundscape (0 = Birdsong 1= Traffic) | 0.26 | 0.29 | 0.378 | -0.72 | 0.83 | 0.388 |
| Landscape (0 = Forest 1 = gray Space) | 0.83 | 0.29 | 0.005** | -1.26 | 0.83 | 0.130 |
| Soundscape X Landscape | 0.24 | 0.29 | 0.394 | -1.15 | 0.83 | 0.168 |
| Age | -0.47 | 0.38 | 0.223 | -0.91 | 0.79 | 0.255 |
| Gender (0 = Male 1 = Non-Male) | -3.89 | 1.46 | 0.009** | 6.53 | 3.05 | 0.035* |
| Random effect | Variance estimate | % Total variance | P | Variance estimate | % Total variance | P |
| Participant | 186.37 | 85.21 | .0001*** | 779.12 | 74.59 | .0001*** |
Linear mixed model results for control period (n = 95).
*, **, *** denote statistical significance of parameter estimate at α = 0.05, 0.01, and 0.001, respectively.
HRV was higher for birdsong, regardless of landscape (b = -1.38, SE = 0.70, p = .049; Table 2). We did not detect a landscape effect (b = -0.61, SE = 0.70, p = .380) or soundscape × landscape interaction effect on HRV (b = 0.36, SE = 0.70, p = .603). Average HR was lower in the forest than the gray space treatment, regardless of soundscape (b = 0.65, SE = 0.24, p = .007; Table 2). We did not detect an effect of soundscape (b = 0.38, SE = 0.24, p = .114) or a soundscape × landscape interaction effect on HR (b = -0.11, SE = 0.24, p = .638). Gender predicted HR during both the control period (b = -3.89, SE 1.46, p = .009) and the treatment period (b = -3.72, SE = 1.46, p = .013), with women reporting lower HR. Gender also predicted control-period HRV (b = 6.53, SE = 3.05, p = .035) but not treatment period HRV (b = 5.04, SE = 3.22, p = .121), with women showing higher HRV. Age did not predict HR or HRV in either period (all p >.22). Overall, landscape was associated with lower HR in the forest during both the control (Table 1) and treatment periods (Table 2), whereas soundscape was associated with higher HRV under birdsong during the treatment period only (Table 2).
Table 2
| Variables | Heart rate | Heart rate variability | ||||
|---|---|---|---|---|---|---|
| B | SE | P | B | SE | P | |
| Soundscape (0 = Birdsong 1= Traffic) | 0.38 | 0.24 | 0.114 | -1.38 | 0.70 | 0.049* |
| Landscape (0 = Forest 1 = gray Space) | 0.65 | 0.24 | 0.008** | -0.61 | 0.70 | 0.380 |
| Soundscape X Landscape | -0.11 | 0.24 | 0.638 | 0.36 | 0.70 | 0.603 |
| Age | -0.42 | 0.38 | 0.274 | -0.98 | 0.84 | 0.246 |
| Gender (0 = Male 1 = Non-Male) | -3.72 | 1.46 | 0.013** | 5.04 | 3.22 | 0.121 |
| Random effect | Variance estimate | % Total variance | P | Variance estimate | % Total variance | P |
| Participant | 187.47 | 89.19 | .0001*** | 893.44 | 82.68 | .0001*** |
Linear mixed model results for treatment period (n = 95).
*, **, *** denote statistical significance of parameter estimate at α = 0.05, 0.01, and 0.001, respectively.
Discussion
Results from our study provided support for hypothesized reductions in physiological stress from exposure to nature, but beneficial effects for HR and HRV were elicited by different aspects of the nature experience. Specifically, exposure to the forest landscape reduced heart rate more than exposure to the grey-space. Conversely, birdsong increased HRV (measured as RMSSD) relative to traffic noise. We did not detect evidence of incongruent auditory and visual nature cues imposing a cognitive cost specific to mismatched conditions as predicted by cross-modal congruence frameworks (Olivetti Belardinelli et al., 2004, Van Renterghem and Lippens, 2024). These results are more consistent with an additive account of restorative pathways than a congruence-dependent one. The visual landscape and the auditory soundscape act on different components of autonomic function rather than requiring alignment between the two, consistent with prior work suggesting nature’s benefits operate through multiple, partially independent pathways (; ). Although we did not detect significant treatment effects for landscape on HRV or soundscape on HR, the results consistently aligned with predictions: forest treatment had higher HRV and birdsong elicited lower HR. Significant effects for these treatments might therefore be detected by future research with larger sample sizes.
The positive effect of birdsong on HRV may be explained by enhanced parasympathetic activation in response to natural acoustic environments. HRV is sensitive to short-term changes in autonomic recovery (Shaffer and Ginsberg, 2017). Birdsong may promote this recovery by signaling a safe, low-threat environment, reducing vigilance and allowing for greater parasympathetic activation. In contrast, traffic noise is acoustically unpredictable and evolutionarily associated with human activity and potential hazards, increasing physiological arousal even when participants are not consciously distressed. This interpretation is consistent with previous studies showing that nature sounds facilitate autonomic recovery following stress whereas anthropogenic noise impairs it (; ). Our study extends those findings by suggesting that these autonomic effects occur regardless of the accompanying visual landscape.
The association of forest exposure with lower HR is consistent with SRT’s account of nonthreatening natural settings reducing physiological stress (Ulrich et al., 1991). Notably, this association held independent of whether participants heard birdsong, traffic, or silence (during the 5-minute control period), suggesting that the visual characteristics of the landscape exerted a robust influence on cardiovascular activity. These results align with the stress-reducing effects of forests, parks, and other natural visual environments documented in recent studies (Yao et al., 2021) and also indicates that these effects may operate independently of concurrent auditory input, at least over the short duration examined here. The interaction of visual and auditory components of environments might impact people’s perceptions and satisfaction with those spaces (; Xu and Wu, 2021), but it is unclear if those interactions might also yield synergistic benefits for physiological measures of stress reduction. More research is needed to understand the impacts of complex audio-visual sensescapes on psycho-physiological health (; ).
The independent effects of forest and birdsong, combined with lack of evidence for hypothesized congruence effects, may provide valuable insights for designing health-inducing urban landscapes. Substantial research has highlighted the beneficial effects of forest exposure on human health and well-being (Stier-Jarmer et al., 2021), including the value of forest-based therapies for treating mental health problems (; Rosa et al., 2021). But there is growing evidence to support the management of soundscapes, in addition to landscapes, as a health promotion tool (; Pijanowski et al., 2011). Although these two approaches might generally work better in congruent unison (), our results show that natural landscapes and soundscapes can also generate health benefits independently. Birdsong can reduce stress even in gray spaces, and forests can benefit health even when traffic dominates the soundscape. These findings imply that efforts to nurture human health through natural landscapes need not be limited to contexts where both forest landscapes and birdsong soundscapes are restored and integrated - an immersive situation that might be challenging to achieve in highly developed urban areas. Instead, our results support the idea that exposure to any type of “nearby nature” confers multiple health benefits (), even if that exposure comes in small doses such as a view of trees () or listening to a birdsong (). In areas with relatively high traffic noise, retaining patches of planted or naturally regenerated vegetation can facilitate stress reduction for humans even if traffic noise cannot be fully mitigated (Ow and Ghosh, 2017). Similarly, even in gray spaces where trees cannot be the dominant landscape feature, promoting bird presence and diversity can yield health benefits: bird richness has been shown to mediate the relationship between green space and mental health outcomes, with greenspace design that supports bird habitat linked to lower rates of poor mental health independent of tree cover (), and bird diversity more broadly shows a robust positive association with mental health across large-scale population data (Methorst, 2024). Incorporating bird-supportive habitat features into green infrastructure alongside forested areas where feasible, could inform the planning and implementation of campus landscapes, which are increasingly designed to bolster student health outcome (; ).
Future research may address several important limitations of this study. First, conducting the research in-situ rather than in a laboratory created logistical constraints on treatment time, instrumentation availability, and ability to control environmental factors. For instance, the control (3.5 minute) and treatment (8.5 minute) times were asymmetrical to reduce participant burden while still ensuring treatment times were similar to those in the literature (Meredith et al., 2020). Both equal-length windows between the control and treatment, and longer treatment times, would be beneficial for future research, given that prolonged (> 30 minutes) exposure to nature is often needed to reduce measures of physiological stress (Shanahan et al., 2016; ). However, it should be noted that observed significant changes in electrodermal activity, another common indicator of stress, after just 3 minutes of nature exposure. Additional work could help determine whether HRV is the primary physiological response to birdsong and forested landscape exposure, or if other measures of physiological stress would be more sensitive, particularly after longer-duration treatments (e.g., cortisol; ). Our findings also highlight the need for more work exploring the optimal frequency, duration, location, and sensory stimulation of nature dosage required to generate positive mental health impacts (Meredith et al., 2020; ).
Similarly, future research with instrumentation to measure headphone-level outputs could ensure sound pressure levels are the same across participants, reducing the need to rely on a participant-level random effect to account for loudness differences. Measuring and including body mass index, a known driver of HRV (), would also reduce the reliance on the participant-level random effect. Although treatment order was randomized and blocked to eliminate confounding effects of pre-session activities (e.g., caffeine intake, exercises, feed consumption), controlling more of those activities in future research would remove noise from the data and likely improve statistical sensitivity to treatments. We controlled for gender in our study, attempting to mitigate the complex relationship between gender, HR, and HRV (Ryan et al., 1994). This study also used a single-exemplar soundscape for birdsong and traffic, leaving open the possibility of acoustic properties of the recordings that were not determined by traffic and birdsong impacting HR and HRV. Future research randomly assigning birdsong or traffic noise from a larger sample of recordings would minimize that limitation. Finally, generalizability is limited by participants being students at a single institution who, for the most part, majored in nature-focused degrees. This group may have a positive disposition toward nature exposure compared to the general public, and that nature affinity could upwardly bias the observed effects. Alternatively, and arguably more likely given past research (Stevenson et al., 2013; ), the sample of participants likely faced a ceiling effect on treatment response, a common challenge in health research (), given they were more likely to already spend time in nature. Past research suggests the health benefits of nature exposure, including birdsong, might accrue most to people who have limited access to nature (Rigolon et al., 2021; Methorst, 2024). These potential biases can be untangled by future research with more diverse participants, and by measuring the time participants spend in nature prior to treatments; ultimately, however, this study demonstrates that even a brief exposure to birdsong soundscapes and forest landscapes produces detectable autonomic benefits in an accessible urban campus setting.
Statements
Data availability statement
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.
Ethics statement
The studies involving humans were approved by North Carolina State University Institutional Review Board for the use of human subjects in research. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.
Author contributions
TF: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. PD: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. JH: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. LL: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. HD: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. JW: Writing – original draft, Writing – review & editing. IH: Writing – original draft, Writing – review & editing. MP: Writing – original draft, Writing – review & editing. KM: Conceptualization, Formal analysis, Investigation, Project administration, Writing – original draft, Writing – review & editing. JK: Writing – original draft, Writing – review & editing. EF: Writing – original draft, Writing – review & editing. GB: Writing – original draft, Writing – review & editing. CMc: Writing – original draft, Writing – review & editing. CB: Writing – original draft, Writing – review & editing. IM: Conceptualization, Investigation, Methodology, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. CMo: Conceptualization, Investigation, Methodology, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing. MP: Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Validation, Visualization, Writing – original draft, Writing – review & editing.
Funding
The author(s) declared that financial support was not received for this work and/or its publication.
Conflict of interest
The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declared that generative AI was not used in the creation of this manuscript.
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Supplementary material
The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fbirs.2026.1884835/full#supplementary-material
References
1
AghabozorgiK.van der JagtA.BellS.SmithH. (2025). The role of university campus landscape characteristics in students’ mental health. Urban For. Urban Greening111, 128863. doi: 10.1016/j.ufug.2025.128863
2
AhmedN.BarnettP.GreenburghA.PemovskaT.StefanidouT.LyonsN.et al. (2023). Mental health in Europe during the COVID-19 pandemic: a systematic review. Lancet Psychiatry10, 537–556. doi: 10.1016/S2215-0366(23)00113-X
3
AlvarssonJ. J.WiensS.NilssonM. E. (2010). Stress recovery during exposure to nature sound and environmental noise. Int. J. Environ. Res. Public Health7, 1036–1046. doi: 10.3390/ijerph7031036
4
AndrewsJ. G.AmmiratiR. J.AndrewsJ. M. (2025). Birding benefits: a review of mental health, cognitive, social, and conservation impacts. Ecopsychology. 17 (1), 1–17. doi: 10.1089/eco.2024.0019
5
AntonelliM.DonelliD.CarloneL.MagginiV.FirenzuoliF.BedeschiE. (2022). Effects of forest bathing (shinrin-yoku) on individual well-being: an umbrella review. Int. J. Environ. Health Res.32, 1842–1867. doi: 10.1080/09603123.2021.1919293
6
BeallJ. M.JacksonS. B.CasolaW. R.PetersonM. N.LarsonL. R.StevensonK. T.et al. (2022). Self-reported participation in outdoor and nature-based recreation before and during the COVID-19 pandemic supports psychological health and well-being. Wellbeing Space Soc3, 100094. doi: 10.1016/j.wss.2022.100094
7
BenfieldJ. A.BellP. A.TroupL. J.SoderstromN. C. (2010). Aesthetic and affective effects of vocal and traffic noise on natural landscape assessment. J. Environ. Psychol.30, 103–111. doi: 10.1016/j.jenvp.2009.10.002
8
BenfieldJ. A.TaffB. D.NewmanP.SmythJ. (2014). Natural sound facilitates mood recovery. Ecopsychology6, 183–188. doi: 10.1089/eco.2014.0028
9
BettmannJ. E.SpeelmanE.JolleyA.CasucciT. (2025). A systematic review and meta-analysis on the effect of nature exposure dose on adults with mental illness. Behav. Sci.15, 153. doi: 10.3390/bs15020153
10
BoydF. (2022). Between the library and lectures: How can nature be integrated into university infrastructure to improve students’ mental health. Front. Psychol.13, 865422. doi: 10.3389/fpsyg.2022.865422
11
BratmanG. N.AndersonC. B.BermanM. G.CochranB.FlandersJ.FolkeC.et al. (2019). Nature and mental health: An ecosystem service perspective. Sci. Adv. doi: 10.1126/sciadv.aax0903
12
BratmanG. N.BembibreC.DailyG. C.DotyR. L.HummelT.JacobsL. F.et al. (2024). Nature and human well-being: The olfactory pathway. Sci. Adv.10, eadn3028. doi: 10.1126/sciadv.adn3028
13
BuxtonR. T.PearsonA. L.AllouC.FristrupK.WittemyerG. (2021). A synthesis of health benefits of natural sounds and their distribution in national parks. Proc. Natl. Acad. Sci.118, e2013097118. doi: 10.1073/pnas.2013097118
14
ChenS.WangH.XuW. (2025). Bird richness as a mediator between greenspace and mental health relationships. Landscape Urban Plann.259, 105360. doi: 10.1016/j.landurbplan.2025.105360
15
ChenH.ZhongX.ShaF.WuY.LinW.YanH.et al. (2026). Mechanisms linking urban plant landscape spatial characteristics to stress regulation and attention recovery. Land Degrad. Dev.37, 347–368. doi: 10.1002/ldr.70114
16
ChengL. J.PanT.ChenL. A.ChengJ. Y.MulhernB.DevlinN.et al. (2024). The ceiling effects of EQ-5D-3L and 5L in general population health surveys: a systematic review and meta-analysis. Value Health27, 986–997. doi: 10.1016/j.jval.2024.02.018
17
CotillonS.MathisM. (2016). “ Tree cover mapping tool—documentation and user manual (ver 10, March 2016),” in Us Geological Survey Open-File Report 2016–1067, 1–11. doi: 10.3133/ofr20161067
18
CoxD. T.ShanahanD. F.HudsonH. L.FullerR. A.AndersonK.HancockS.et al. (2017). Doses of nearby nature simultaneously associated with multiple health benefits. Int. J. Environ. Res. Public Health14, 172. doi: 10.3390/ijerph14020172
19
DaiX.YangB.ZhouY.HuJ.ChenJ.RenY.et al. (2026). From quantity to visual quality: Unraveling nonlinear thresholds of campus nature exposure for precision mental health restoration. Build. Environ.294, 114428. doi: 10.1016/j.buildenv.2026.114428
20
DalyM.SutinA. R.RobinsonE. (2022). Longitudinal changes in mental health and the COVID-19 pandemic: evidence from the UK Household Longitudinal Study. Psychol. Med.52, 2549–2558. doi: 10.1017/s0033291720004432
21
DeGiorgioC. M.MillerP.MeymandiS.ChinA.EppsJ.GordonS.et al. (2010). RMSSD, a measure of vagus-mediated heart rate variability, is associated with risk factors for SUDEP: the SUDEP-7 Inventory. Epilepsy Behav.19, 78–81. doi: 10.1016/j.yebeh.2010.06.011
22
DollB. (2010). Rocky branch stream restoration and greenway project. Available online at: https://ncseagrant.ncsu.edu/ncseagrant_docs/products/2010s/rocky_branch_projectsummary.pdf (Accessed May 18, 2025).
23
DuH.ZhouF.CaiY.LiC.XuY. (2021). Research on public health and well-being associated to the vegetation configuration of urban green space: a case study of Shanghai, China. Urban For. Urban Greening59, 126990. doi: 10.1016/j.ufug.2021.126990
24
FerraroD. M.MillerZ. D.FergusonL. A.TaffB. D.BarberJ. R.NewmanP.et al. (2020). The phantom chorus: birdsong boosts human well-being in protected areas. Proc. R. Soc. B.287, 20201811. doi: 10.1098/rspb.2020.1811
25
García-MartínM.KoleckaN.HunzikerM.GrazL.DopicoJ.SchäfferB.et al. (2025). The role of greenness and road traffic noise for psychological restoration in everyday environments: A participatory mapping approach. Landscape Urban Plann.259, 105339. doi: 10.1016/j.landurbplan.2025.105339
26
GilaniT. A.MirM. S. (2021). A study on the assessment of traffic noise induced annoyance and awareness levels about the potential health effects among residents living around a noise-sensitive area. Environ. Sci. pollut. Res.28, 63045–63064. doi: 10.1007/s11356-021-15208-3
27
GuoL. N.ZhaoR. L.RenA. H.NiuL. X.ZhangY. L. (2020). Stress recovery of campus street trees as visual stimuli on graduate students in autumn. Int. J. Environ. Res. Public Health17, 148. doi: 10.3390/ijerph17010148
28
HedblomM.GunnarssonB.SchaeferM.KnezI.ThorssonP.LundströmJ. N. (2019). Sounds of nature in the city: No evidence of bird song improving stress recovery. Int. J. Environ. Res. Public Health16, 1390. doi: 10.3390/ijerph16081390
29
IyendoT. O.WelchD.UwajehP. C. (2024). Soundscape and natural landscape as a design construct for improving psycho-physiological health in cities: a semi-systematic literature review. Cities Health8, 447–485. doi: 10.1080/23748834.2023.2280288
30
JacksonS. B.StevensonK. T.LarsonL. R.PetersonM. N.SeekampE. (2021). Outdoor activity participation improves adolescents’ mental health and well-being during the COVID-19 pandemic. Int. J. Environ. Res. Public Health18, 2506. doi: 10.3390/ijerph18052506
31
JenningsV. L.LarsonC. K.LarsonL. R. (2016). Ecosystem services and preventive medicine: a natural connection. Am. J. Prev. Med.50, 642–645. doi: 10.1016/j.amepre.2015.11.001
32
JeonJ. Y.JoH. I. (2020). Effects of audio-visual interactions on soundscape and landscape perception and their influence on satisfaction with the urban environment. Build. Environ.169, 106544. doi: 10.1016/j.buildenv.2019.106544
33
JonesR.TarterR.RossA. M. (2021). Greenspace interventions, stress and cortisol: a scoping review. Int. J. Environ. Res. Public Health18, 2802. doi: 10.3390/ijerph18062802
34
KlepeisN.NelsonW.OttW.RobinsonJ.TsangA.SwitzerP.et al. (2001). The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants. J. Exposure Sci. Environ. Epidemiol.11, 231–245. doi: 10.1038/sj.jea.7500165
35
KoenigJ.JarczokM. N.WarthM.EllisR. J.BachC.HilleckeT. K.et al. (2014). Body mass index is related to autonomic nervous system activity as measured by heart rate variability—a replication using short term measurements. J. Nutr. Health Aging18, 300–302. doi: 10.1007/s12603-014-0022-6
36
KorpelaK.HartigT. (1996). Restorative qualities of favorite places. J. Environ. Psychol.16, 221–233. Available online at: https://psycnet.apa.org/doi/10.1006/jevp.1996.0018 (Accessed May 21, 2025).
37
KorpiloS.NybergE.VierikkoK.OjalaA.KasevaJ.LehtimäkiJ.et al. (2024). Landscape and soundscape quality promote stress recovery in nearby urban nature: a multisensory field experiment. Urban For. Urban Greening95, 128286. doi: 10.1016/j.ufug.2024.128286
38
KouL.WeiC.ChiC. G.XuH. (2025). Understanding sensescapes and restorative effects of nature-based destinations: a mixed-methods approach. J. Sustain. Tourism33, 243–264. doi: 10.1080/09669582.2024.2324021
39
KumpulainenS.EsmaeilzadehS.PesolaA. (2024). Assessing the well-being benefits of VR nature experiences on group: Heart rate variability insights from a cross-over study. J. Environ. Psychol.97, 102366. doi: 10.1016/j.jenvp.2024.102366
40
LarsonL. R.MullenbachL. E.BrowningM. H.RigolonA.ThomsenJ.MetcalfE. C.et al. (2022). Greenspace and park use associated with less emotional distress among college students in the United States during the COVID-19 pandemic. Environ. Res.204, 112367. doi: 10.1016/j.envres.2021.112367
41
LipsonS. K.ZhouS.AbelsonS.HeinzeJ.JirsaM.MorigneyJ.et al. (2022). Trends in college student mental health and help-seeking by race/ethnicity: Findings from the national healthy minds study 2013-2021. J. Affect. Disord.306, 138–147. doi: 10.1016/j.jad.2022.03.038
42
LiuY.FrazierP. A.PortaC. M.LustK. (2022). Mental health of US undergraduate and graduate students before and during the COVID-19 pandemic: Differences across sociodemographic groups. Psychiatry Res.309, 114428. doi: 10.1016/j.psychres.2022.114428
43
LiuC.JingX.ShiJ.LiJ.ZhangY.GaoW. (2024). Effects of natural sound on human stress recovery based on EEG techniques. J. Environ. Psychol.97, 102365. doi: 10.1016/j.jenvp.2024.102365
44
LiuG.ZouJ.QiaoM.ZhuH.YangY.GuanH.et al. (2023). Stress recovery at home: Effects of the indoor visual and auditory stimuli in buildings. Build. Environ.244, 110752. doi: 10.1016/j.buildenv.2023.110752
45
MaddockJ. E.JohnsonS. S. (2024). Spending time in nature: the overlooked health behavior. Am. J. Health Promot.38, 124–148. doi: 10.1177/08901171231210806a
46
MarkevychI.SchoiererJ.HartigT.ChudnovskyA.HystadP.DzhambovA. M.et al. (2017). Exploring pathways linking greenspace to health: Theoretical and methodological guidance. Environ. Res.158, 301–317. doi: 10.1016/j.envres.2017.06.028
47
McGorryP.GunasiriH.MeiC.RiceS.GaoC. X. (2025). The youth mental health crisis: analysis and solutions. Front. Psychiatry15. doi: 10.3389/fpsyt.2024.1517533
48
MeredithG. R.RakowD. A.EldermireE. R.MadsenC. G.ShelleyS. P.SachsN. A. (2020). Minimum time dose in nature to positively impact the mental health of college-aged students, and how to measure it: A scoping review. Front. Psychol.10, 488425. doi: 10.3389/fpsyg.2019.02942
49
MethorstJ. (2024). Positive relationship between bird diversity and human mental health: an analysis of repeated cross-sectional data. Lancet Planet. Health8, e285–e296. doi: 10.1016/s2542-5196(24)00023-8
50
Moulaythami. (2020). Cars passing on the highway, microphone above a bridge recorder. Available online at: https://freesound.org/people/Moulaythami/sounds/544165/ (Accessed November 4, 2025).
51
Nature of Americans (2017). Media Use Increases While Outdoor Time Decreases Among Older Children. Available online at: https://natureofamericans.org/findings/viz/media-use-increases-while-outdoor-time-decreases-among-older-children.
52
Olivetti BelardinelliM.SestieriC.Di MatteoR.DguF.Del GrattaC.FerrettiA.et al. (2004). Audio-visual crossmodal interactions in environmental perception: an fMRI investigation. Cognit. Process.5, 167–174. doi: 10.1007/s10339-004-0024-0
53
OsborneM. T.RadfarA.HassanM. Z. O.AbohashemS.OberfeldB.PatrichT.et al. (2020). A neurobiological mechanism linking transportation noise to cardiovascular disease in humans. Eur. Heart J.41, 772–782. doi: 10.1093/eurheartj/ehz820
54
OwL. F.GhoshS. (2017). Urban cities and road traffic noise: Reduction through vegetation. Appl. Acoust.120, 15–20. doi: 10.1016/j.apacoust.2017.01.007
55
PetersonR. T. (2020). Peterson Field Guide to Birds of North America. 2nd ed (Boston, MA: Houghton Mifflin Harcourt).
56
PetersonM. N.LarsonL. R.HippA.BeallJ. M.LeroseC.DesrochersH.et al. (2024). Birdwatching linked to increased psychological well-being on college campuses: A pilot scale experimental study. J. Environ. Psychol.96, 102306. doi: 10.1016/j.jenvp.2024.102306
57
PijanowskiB. C.Villanueva-RiveraL. J.DumyahnS. L.FarinaA.KrauseB. L.NapoletanoB. M.et al. (2011). Soundscape ecology: the science of sound in the landscape. BioScience61, 203–216. doi: 10.1525/bio.2011.61.3.6
58
Plana-RipollO.MomenN. C.McGrathJ. J.WimberleyT.BrikellI.SchendelD.et al. (2022). Temporal changes in sex-and age-specific incidence profiles of mental disorders—a nationwide study from 1970 to 2016. Acta Psychiatrica Scand.145, 604–614. doi: 10.1111/acps.13410
59
RandlerC.VanhöfenJ.HärtelT.NeunhoefferF.EngeserC.FischerC. (2023). Psychological restoration depends on curiosity, motivation, and species richness during a guided bird walk in a suburban blue space. Front. Psychol.14, 1176202. doi: 10.3389/fpsyg.2023.1176202
60
RatcliffeE.GaterslebenB.SowdenP. T. (2013). Bird sounds and their contributions to perceived attention restoration and stress recovery. J. Environ. Psychol.36, 221–228. doi: 10.1016/j.jenvp.2013.08.004
61
RatcliffeE.GaterslebenB.SowdenP. (2016). Associations with bird sounds: How do they relate to perceived restorative potential? J. Environ. Psychol.47, 136–144. doi: 10.1016/j.jenvp.2016.05.009
62
RatcliffeE.GaterslebenB.SowdenP. T. (2018). Predicting the perceived restorative potential of bird sounds through acoustics and aesthetics. Environ. Behav.52, 371–400. doi: 10.1177/0013916518806952
63
RigolonA.BrowningM. H.McAnirlinO.YoonH. (2021). Green space and health equity: a systematic review on the potential of green space to reduce health disparities. Int. J. Environ. Res. Public Health18, 2563. doi: 10.3390/ijerph18052563
64
RosaC. D.LarsonL. R.ColladoS.ProficeC. C. (2021). Forest therapy can prevent and treat depression: Evidence from meta-analyses. Urban For. Urban Greening57, 126943. doi: 10.1016/j.ufug.2020.126943
65
RyanS. M.GoldbergerA. L.PincusS. M.MietusJ.LipsitzL. A. (1994). Gender-and age-related differences in heart rate dynamics: are women more complex than men? J. Am. Coll. Cardiol.24, 1700–1707. doi: 10.1016/0735-1097(94)90177-5
66
ScottE. E.LoTemplioS. B.McDonnellA. S.McNayG. D.GreenbergK.McKinneyT.et al. (2020). The autonomic nervous system in its natural environment: immersion in nature is associated with changes in heart rate and heart rate variability. Psychophysiology58, e13698. doi: 10.1111/psyp.13698
67
SeppänenO. A.FiskW. (2006). Some quantitative relations between indoor environmental quality and work performance or health. HVAC&R Res.12, 957–973. doi: 10.1080/10789669.2006.10391446
68
ShafferF.GinsbergJ. P. (2017). An overview of heart rate variability metrics and norms. Front. Public Health5, 258. doi: 10.3389/fpubh.2017.00258
69
ShafferF.McCratyR.ZerrC. L. (2014). A healthy heart is not a metronome: an integrative review of the heart's anatomy and heart rate variability. Front. Psychol.5, 1040. doi: 10.3389/fpsyg.2014.01040
70
ShanahanD. F.BushR.GastonK. J.LinG. B.DeanJ.BarberE.et al. (2016). Health benefits from nature experiences depend on dose. Sci. Rep.6, 28551. doi: 10.1038/srep28551
71
ShiH.LuoH.WeiY.ShinW.-S. (2024). The influence of different forest landscapes on physiological and psychological recovery. Forests15, 498. doi: 10.3390/f15030498
72
SingerK. (2023). Crimson mallow & Black needlerush marsh wildlife audio. Available online at: https://freesound.org/people/KevinSonger/sounds/687335/.
73
StevensonK. T.PetersonM. N.BondellH. D.MertigA. G.MooreS. E. (2013). Environmental, institutional, and demographic predictors of environmental literacy among middle school children. PloS One8, e59519. doi: 10.1371/journal.pone.0059519
74
Stier-JarmerM.ThronerV.KirschneckM.ImmichG.FrischD.SchuhA. (2021). The psychological and physical effects of forests on human health: A systematic review of systematic reviews and meta-analyses. Int. J. Environ. Res. Public Health18, 1770. doi: 10.3390/ijerph18041770
75
StigsdotterU. K.EkholmO.SchipperijnJ.ToftagerM.Kamper-JørgensenF.RandrupT. B. (2010). Health promoting outdoor environments-associations between green space, and health, health-related quality of life and stress based on a Danish national representative survey. Scand. J. Public Health38, 411–417. doi: 10.1177/1403494810367468
76
StobbeE.SundermannJ.AsconeL.KühnS. (2022). Birdsongs alleviate anxiety and paranoia in healthy participants. Sci. Rep.12, 16414. doi: 10.1038/s41598-022-20841-0
77
TarvainenM. P.NiskanenJ. P.LipponenJ. A.Ranta-AhoP. O.KarjalainenP. A. (2014). Kubios HRV--heart rate variability analysis software. Comput. Methods Programs Biomed.113, 210–220. doi: 10.1016/j.cmpb.2013.07.024
78
TillmannS.TobinD.AvisonW.GillilandJ. (2018). Mental health benefits of interactions with nature in children and teenagers: A systematic review. J. Epidemiol. Community Health72, 958–966. doi: 10.1136/jech-2018-210436
79
UlrichR.SimonsR.LositoB.FioritoE.MilesM.ZelsonM. (1991). Stress recovery during exposure to natural and urban environments. J. Environ. Psychol.11, 201–230. doi: 10.1016/S0272-4944(05)80184-7
80
Van RenterghemT.LippensA. (2024). The audio-visual incongruency asymmetry. Natural sounds in an urban visual setting are more relaxing than urban sounds in visual nature. Urban For. Urban Greening101, 128514. doi: 10.1016/j.ufug.2024.128514
81
WhiteM. P.AlcockI.GrellierJ.WheelerB. W.HartigT.WarberS. L.et al. (2019). Spending at least 120 minutes a week in nature is associated with good health and wellbeing. Sci. Rep.9, 1–11. doi: 10.1038/s41598-019-44097-3
82
XuX.WuH. (2021). Audio-visual interactions enhance soundscape perception in China’s protected areas. Urban For. Urban Greening61, 127090. doi: 10.1016/j.ufug.2021.127090
83
YaoW.ChenF.WangS.ZhangX. (2021). Impact of exposure to natural and built environments on positive and negative affect: A systematic review and meta-analysis. Front. Public Health9, 758457. doi: 10.3389/fpubh.2021.758457
84
YiK.ZhangJ.ZhangZ.ShiX.DuW.YangL.et al. (2024). Differences in public perceptions of recovery in different urban forests based on birdsong. Forests15, 2217. doi: 10.3390/f15122217
85
YoonH.JeonJ. Y. (2025). Relationship between soundscape perception and psychophysiological responses to virtual environmental events. Virtual Reality29, 11. doi: 10.1007/s10055-024-01087-9
86
ZielonkaN. B.TubmanV.DicksL. V.ButlerS. J. (2024). Increased bird sound diversity in vineyards enhances visitors' tour experience. People Nat.6, 2325–2333. doi: 10.1002/pan3.10721
Summary
Keywords
birdsong, heart rate variability, mental health, stress, traffic
Citation
Ford T, DeMay P, Hipp JA, Larson LR, Desrochers HM, Webb J, Howell I, Pratiwi MA, Meshram K, Kluttz JD, Foy E, Barlow G, McDade C, Bourke CJ, Mali I, Moorman CE and Peterson MN (2026) Exposure to forests and birdsong may reduce physiological stress among college students. Front. Bird Sci. 5:1884835. doi: 10.3389/fbirs.2026.1884835
Received
18 May 2026
Revised
04 August 2026
Accepted
07 August 2026
Published
03 September 2026
Volume
5 - 2026
Edited by
Seunguk Shin, University of Missouri, United States
Reviewed by
George Christopoulos, Nanyang Technological University, Singapore
Petro Katerynych, Taras Shevchenko National University of Kyiv, Ukraine
Updates
Copyright
© 2026 Ford, DeMay, Hipp, Larson, Desrochers, Webb, Howell, Pratiwi, Meshram, Kluttz, Foy, Barlow, McDade, Bourke, Mali, Moorman and Peterson.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Trenton Ford, trford2@ncsu.edu; M. Nils Peterson, mnpeters@ncsu.edu
Disclaimer
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