A Systematic Review of the Behavioral and Physiological Effects of Fireworks Noise on Domestic Dogs

Dogs (Canis familiaris) are like children in that they pay attention to facial expressions, gestures, and gaze, which serve as a means for them to communicate and connect with humans [1, 2]; they possess brain regions for temporal face recognition that they use to determine the meaning behind human language [3, 4], consequently, all these characteristics enable them to play important roles in society, such as police dogs, guide dogs, and search and rescue dogs [5]. Dogs have a global population of approximately 700 million [6] and are the species that have maintained the closest and oldest relationship with humans compared to other domestic species [7, 8], this is how they have earned the title of ‘man’s best friend’.

Noise is the unwanted sound that is omnipresent and causes harm to the biological system of individuals and communities, such as in humans and animals [9-11]; similarly, it is measured in the equivalent continuous A-weighted sound pressure level, with the unit being decibels (dB) [12, 13]. Acoustic pollution is the anthropogenic physical alteration of the environment [14, 15]. There is no universal term to refer to dogs’ fear of noise, and it has different denominations such as noise sensitivity, noise aversion, noise stress, or noise reactivity [16-18]. Furthermore, there are differences between ‘anxiety’ (anticipation of a negative outcome without a specific provoking stimulus), ‘fear’ (adaptive response to a potentially dangerous stimulus), and ‘phobia’ (extreme and enduring reaction, possibly triggered by a low-intensity stimulus, which in human psychiatry is termed irrational) [19-21].

Dogs detect sounds four times farther away than humans because they possess more precise auditory capabilities [22]. Surveys indicate that approximately 50% of dogs are likely to experience extreme reactions to some noise during their lifetime [21, 23], additionally, between 40 and 50% exhibit fearful behavior upon exposure [19]. The most frequent noise sources that cause fear reactions in dogs are sirens and alarms, followed by thunder, fireworks, and gunshots [24, 25], thus, noises associated with machinery and vehicles can provoke fearful, phobic, or anxious responses [26]. Similarly, a study determined that 53.5% of dogs showed fear of other noises (sirens, vacuum cleaners, etc.), 73.8% to gunshots, and 92.9% to fireworks [19], furthermore, the effects caused by fireworks noise included panting, trembling, hiding, fleeing, and increased attention and alertness [24], another study indicated that the sound of thunder causes fear and anxiety [27]. Additionally, in studies measuring noise from fireworks, the majority exceeded the WHO value [28].

In this context, the objective of the research was to determine the effects of fireworks noise on dogs, establishing the following research questions (RQ):

RQ1: What is the geographic distribution of studies by year/country and annual scientific production?

RQ2: Which journal presented the highest number of studies?

RQ3: Which breed was the most studied, and what were the most frequent effects of noise?

RQ4: Which keywords have the highest number of appearances?

For the systematic review, the PRISMA 2020 statement was applied [29], tool that helps to understand, summarize and prepare for review [30].

In order to have a larger number of articles selected for the review, the following inclusion criteria were considered, (1) scientific research articles, (2) worldwide, (3) in all languages (translation services required), and (4) without restriction on publication years up to 2023.

The exclusion criteria discarded (1) duplicated articles, (2) closed-access articles, (3) those with titles and abstracts unrelated to the study’s objective, and (4) qualitative research studies.

The boolean operators ‘AND’/‘OR’ were used to connect the terms, and thus search them in the title, abstract, and keywords. Data collection was carried out from September 11th to December 31st, 2023, in 5 digital databases (Table 1). The following equations were used in the search strategy:

For the selection of articles, 2 authors were grouped in order to extract the information from each digital database, any disagreements were resolved at the end of the selection process by discussing with the corresponding author (MRI), The information collected from the selected articles had to respond to the general objective, and the limitations were resolved by applying the exclusion criteria. In the systematization of article selection, the online tool allowing for the creation of the PRISMA 2020 flow diagram [31] was utilized. Initially, 2 621 772 articles were identified, and after applying the eligibility criteria, 33 articles remained for review (Figure 1).

The CAGR indicates the annual growth of a variable over a period exceeding one year [32], in this regard, with the assistance of the online calculator [33], the annual growth of scientific production (from 1965 to 2023) was determined for its accessibility, speed, and ease of use [34], utilizing the following formula:

$C A G R \%=100 *\left(\left(\frac{V_f}{V i}\right)^{\frac{1}{t}}-1\right)$

where, V_i=Initial value; V_f=Final value; t=Years.

The information was downloaded in CSV to be processed in Microsoft Office Excel 2016 to determine the distribution of studies by year and country, the analysis was performed with VOSviewer 1.6.19. [35], used in the scientific field to represent and visualize bibliometric networks in many colors that will facilitate the discovery and understanding of co-authorship (by number of citations or documents), journals, countries, institutions, and keyword co-occurrence relationships [36-38], thus, it was employed in the study for the analysis of keyword co-occurrence.

The most frequent effects of noise are changes in behavior (fleeing, hiding, restlessness, whining, and cowering) and physiological responses of the dog (excessive salivation, decreased heart rate, loss of appetite, and sleep (Table 2), likewise, common aversive effects of noise include panting, escaping, crouching, hiding, and salivation [39-41].

On the other hand, the most frequent causes of noise aversion are fireworks, gunshots, and thunderstorms [19, 21].

Another frequent effect is the increase in cortisol, which is in response to the stress caused by noise, resulting in excessive salivation in dogs [42]. Likewise, chronic stress damage’s immune function and consequently increases the risk of contracting diseases [43]. The effects found will serve to raise awareness of the harm suffered by dogs, as well as to enact measures to mitigate these impacts, which are currently uncontrolled, much less in developing countries.

In 20% of the studies, dogs were subjected to thunderstorm noises, as the most reported noise phobia causing disorders in dogs are thunderstorms [18, 44, 45], likewise, the prevalence of phobia in the canine population is estimated to range between 15-30% [39].

On the other hand, the most frequent causes of noise aversion are fireworks, gunshots, and thunderstorms [19, 21].

Another frequent effect is the increase in cortisol, which is in response to the stress caused by noise, resulting in excessive salivation in dogs [42], likewise, chronic stress damage’s immune function and consequently increases the risk of contracting diseases [43]. The effects found will serve to raise awareness of the harm suffered by dogs, as well as to enact measures to mitigate these impacts, which are currently uncontrolled, much less in developing countries.

In 20% of the studies, dogs were subjected to thunderstorm noises, as the most reported noise phobia causing disorders in dogs are thunderstorms [18, 44, 45], likewise, the prevalence of phobia in the canine population is estimated to range between 15-30% [39].

On the other hand, in their study demonstrated that, in a sample of 2577 dogs, fear of thunderstorms was the second most common phobia (31%) followed by fear of fireworks (32%) [46], while another survey conducted with 337 dog owners indicated that 86% and 74% of their dogs had phobia of thunderstorm and fireworks noise, respectively [47], these studies support the findings of the review, with fireworks being the second most common noise to which dogs were subjected. Dog owners and handlers are the main actors in solving the problem, they should demand preventive measures from their authorities and enforce the provisions implemented in the future.

On the other hand, the most frequent causes of noise aversion are fireworks, gunshots, and thunderstorms [19, 21]. An increase in cortisol, which is in response to the stress caused by noise, resulting in excessive salivation in dogs [42], likewise, chronic stress damages immune function and consequently increases the risk of contracting diseases [43]. The effects found will serve to raise awareness of the harm suffered by dogs, as well as to enact measures to mitigate these impacts, which are currently uncontrolled, much less in developing countries.

In 20% of the studies, dogs were subjected to thunderstorm noises, as the most reported noise phobia causing disorders in dogs are thunderstorms [18, 44, 45], likewise, the prevalence of phobia in the canine population is estimated to range between 15-30% [39].

On the other hand, in their study demonstrated that, in a sample of 2577 dogs, fear of thunderstorms was the second most common phobia (31%) followed by fear of fireworks (32%) [46], while another survey conducted with 337 dog owners indicated that 86% respectively and 74% of their dogs had phobia of thunderstorm and fireworks noise [47], these studies support the findings of the review, with fireworks being the second most common noise to which dogs were subjected. Dog owners and handlers are the main actors in solving the problem, they should demand that authorities take preventive measures and should ensure the enforcement of any provisions implemented in the future.

Based on the results, future research on hormonal changes, neurotransmitters and specific neuronal responses to noise could be proposed, as well as the creation and validation of tools to help measure stress through observation and behaviors, hormonal analysis and non-invasive measures. Moreover, it would be complemented with the study of pharmacological and non-pharmacological interventions to mitigate fear and anxiety in dogs.

The scientific production has evolved steadily from 1965 to 2020, followed by a gradual decline up to the present, the years with the highest number of publications are 2018 and 2020, both with 4 publications (Figure 2). The CAGR is an important instrument to determine the growth per year of a set of articles in a given subject, in this sense, the compound annual growth rate of scientific production between 1965 and 2023 is 6.11%, indicating a low annual growth rate up to the present.

The geographical distribution of studies with the highest number of publications is the United States (9) (Figure 3); hearing loss is the third most common chronic disease in the country, despite people having access to hearing protection as well as recreational recommendations and occupational regulations [81-83]. Comparing this with the canine population, which does not have these opportunities, it is likely that the risk of hearing loss is higher for dogs, due to the importance of noise effects on dogs, it becomes the country with the highest number of publications, additionally, the country ranks second in the Global Innovation Index 2022, investing 3.45% of its GDP in research and development in 2021 [84].

The keywords with the highest number of appearances per word are ‘dog’ and ‘magnetic resonance imaging’ with 132 and 44 appearances, respectively, on the other hand, 6 clusters were formed, with the word ‘dog’ being the cluster with the highest linkage with 9 keywords (Figure 4).

The research peaked in 2018 and 2020, the annual growth of scientific production indicates that it will continue to decrease as the years progress, which is concerning considering that these pets are a fundamental part of human daily life, furthermore, the country with the highest number of publications was the United States. On the other hand, in the studies, dogs were mostly subjected to noises from thunderstorms and fireworks, which are impulsive noises with high levels of continuous equivalent sound pressure that they are sporadically exposed to and cause serious harm.

The most frequent effects on dogs were changes in behavior and physiological responses, which are detrimental as they generate stress and inhibit their normal activity in tasks they may be assigned to (such as police work, guiding, search, and rescue). Dog owners should take preventive measures to mitigate the effects of noise generated by fireworks through insulation, and environmental regulations should prohibit the use of fireworks at events, thus helping to reduce noise and air pollution. For future research, it is recommended to determine if the effects of noise manifest in the same way across different dog breeds.