Vocalizations by red fox ( Vulpes vulpes ) in natural and climatic conditions of Mordovia (Middle Volga region)

. The daily and seasonal vocalization of the red fox was traced. Year-round studies were carried out using digital voice recorders. Fox barking was recorded in the frequency range from 700 to 3600 Hz. The cackling of the fox was recorded in the frequency range from 500 to 2500 Hz. Fox calls were recorded in all seasons of the year, but the most pronounced peaks of prolonged activity in the year were recorded in spring and autumn. The vocal activity of the red fox was noted for the entire period of the study from 17:51 to 01:38. During this period, the total duration of calls in the red fox varied from 34 sec to 27 min per day, 4 min on average. 86% of all call registrations in the region occurred before midnight, the rest (14%) after midnight. Vocalization began after sunset for an average of 2 h 49 min.


Introduction
The vocalization of different animal species carries a lot of scientific information about the various features of their biology and ecology.There are very few works devoted to this topic, most of them affect only certain groups of animals [1][2][3].Although, undoubtedly, studies of this nature must be carried out in relation to many actively vocalizing species.Literature sources devoted to representatives of the Canidae order (Canidae) do not contain detailed information about the time and timing of the activity of different species.Often only approximate dates of vocal activity are given.One of these species is the red fox Vulpes vulpes L., 1758.For Russia, it is not known that detailed year-round studies on the vocalization of the red fox in nature have been carried out.Of undoubted interest, at what hours of the day do foxes show the greatest and least vocal activity?And also how vocalization changes by seasons and months.Also, what are the possible reasons for this?
Despite such a significant significance and priority of studying the ecology and biology of the red fox, there are very few works devoted to its vocalization.It is extremely interesting what the daily and seasonal vocal activity of the red fox depends on, whether it is possible to influence meteorological parameters on it.
The purpose of the research is to characterize the vocal activity by red fox, taking into account the influence of meteorological parameters in the natural habitat using the method of recording acoustic signals using digital voice recorders.

Materials and methods
The material for this article was audio recordings of the vocal activity of the red fox, obtained using portable voice recorders Olympus VN-416PC, VN-406PC, VN-712PC, as well as diary recordings of calls recorded directly on the ground.The technique was applied from previous experience in studying the activity of different animal species [4][5][6][7][8].Direct recordings of the calls of the red fox by the counter on the ground were carried out from 2008 to 2023.Voice activity of the red fox was recorded using voice recorders in different regions of the Republic of Mordovia (53º38'-55º11'N and 42º11'-46º45'E) in the period from 2015 to 2023.The climate of the region is temperate continental with a pronounced change of seasons throughout the year.The average annual air temperature ranges from 3.5 to 4.0 °С.The average annual rainfall in the territory is 480 mm.
Since the red fox is widespread in Mordovia and is a common species, as well as in the Middle Volga region [9], therefore, the analysis used the total sample for all districts.At the preliminary stage of the research, individual differences in the vocal activity of the red fox were not revealed, therefore, the results for the total sample are considered.In addition, in the scientific literature, we do not know of a reliably proven relationship between the nature of vocalization and the sex of foxes.
Cameral processing of the obtained audio recordings was carried out using AIMP (2007) and Audacity (2015) computer programs.Initially, the received audio recordings from voice recorders were converted in the AIMP program, from WMA to WAV format and divided into short audio recordings of 70 hours.Further spectrograms were obtained using the AUDACITY program.The purpose of the spectrograms was to identify calls more efficiently (faster) and to easily check what time vocalizations started and ended.On the spectrograms, the beginning and end of voice activity were noted in the evening, night and morning hours during the analysis of the received records.The duration of individual periods of vocalization was determined as the difference in time between the beginning and end of a series of calls.When identifying the timing of the beginning and end of acoustic activity, only those days were taken into account when the foxes called in the time interval up to 5 hours relative to sunset and sunrise, respectively.In the presence of calls, but their absence earlier or later than this interval from sunset or sunrise, these days were not taken into account.The analysis was carried out by months and seasons of the year.Similarly, a possible dependence of vocalization on the phases of the moon was revealed.At the same time, the meteorological conditions of the area were assessed, under which the vocal activity of the fox was recorded.The data of the following weather conditions were recorded: temperature (°C), wind force (m/s), cloud cover (%), pressure (mm Hg).We used data from the Bolshie Berezniki weather station (http://rp5.ru;http://nuipogoda.ru;http://voshod-solnca.ru; http://ru.astro-scek.com)where hourly variables were displayed.Statistical calculations were carried out using computer programs AtteStat 8 (2002), Microsoft Office Excel (2003) and Past 2.04 (2010).

Results
As a result of the research, 32 audio recordings (more than 2500 h) containing the calls by red fox were obtained from dictaphones and 21 recordings from calls directly when listening on the ground.The calls by red fox were noted in the vicinity of the villages of Ivanova Polyana, Picheury, Michurino, Sokolov Gart (Chamzinsky district), Simkino, Shugurovo, The vocal activity by red fox was noted for the entire period of the study from 17:51 to 01:38.In January, calls were recorded from 22:39 to 23:10.The duration of individual series varied from 44 sec to 2 min 4 sec.The number of calls in the series ranged from 12 to 15 calls.In February, calls were recorded from 19:49 to 20:22.The duration of individual series varied from 30 sec to 3 min 13 sec.The number of calls in the series ranged from 6 to 39 calls.In March, calls were recorded from 19:29 to 22:38.The duration of individual series varied from 12 sec to 10 min.The number of calls in the series ranged from 6 to 112 calls.In April, calls were recorded from 21:19 to 22:48.The duration of individual series varied from 20 sec to 3 min.The number of calls in the series ranged from 3 to 10 calls.In May, calls were recorded from 01:35 to 01:38.The duration of individual series varied from 40 sec to 2 min.The number of calls in the series ranged from 6 to 52 calls.In August, calls were recorded from 22:35 to 22:50.The duration of individual series varied from 14 sec to 20 sec.The number of calls in the series ranged from 7 to 10 calls.In September, calls were recorded from 21:51 to 00:38.The duration of individual series varied from 10 sec to 2 min 4 sec.The number of calls in the series ranged from 12 to 15 calls.In October, calls were recorded from 17:51 to 01:21.The duration of individual series varied from 40 sec to 3 min 12 sec.The number of calls in the series ranged from 11 to 48 calls.
Analysis of vocalization showed the clearest intense peak of red fox activity in spring (61.9% of all recordings per year).The peak of activity is associated with the breeding season.Vocalization is somewhat inferior in autumn (19%), winter (14.3%) and summer (4.8%).The trend in the seasonal vocal activity by red fox is also confirmed by the ratio of the duration of individual daily periods of vocalization in spring, summer, autumn, and winter.The longest duration of vocalization periods was recorded in spring from 1 min 50 sec to 26 min (average 9 min).In autumn, the duration of vocalization periods ranged from 1 min to 8 min 48 sec (on average, 5 min), in winter, from 44 sec to 3 min (on average, 2 min), in summer, from 34 sec to 1 min 48 sec (on average, 40 sec).
The main type of calls recorded in the studies was barking.Fox barking was recorded in the frequency range from 700 to 3600 Hz (Fig. 1).The purpose of barking in a wide frequency range in foxes is due to the establishment of contact between males and females located at a great distance, primarily during the rutting period, as well as during the resettlement of young animals.During the day, more often one period of vocalization was noted before midnight, less often two with an interval of several hours (one before midnight, the second after midnight).The vocalization period consisted either of one series of calls or included up to a maximum of 16 episodes (in March).The number of calls in the series varied from 3 to 112 (23 on average).The intervals between individual barks in the series of calls were 2 to 10 s (4 s on average).The duration of individual series of calls ranged from 12 sec to 10 min (average 2 min 34 sec).The intervals between individual series of calls in continuous periods of activity varied from 16 s to 2 min (38 s on average).Voice activity was recorded in the temperature range from -14 to +17 °C.Most often, this is typical for negative temperatures (-8 to -2 °C).Calls were recorded at wind strength from 1 to 3 m/s, cloudiness from 10 to 30%, pressure from 745 to 769 mm Hg.More than 60% of registrations were noted during the waning moon, the rest during the growing moon.Voice activity during the full moon and new moon is not registered.In the spring, foxes always started to call after sunset from 1:11 to 4:32.Vocalization began after sunset for an average of 2 hours and 49 minutes.Vocalization always ended before dawn (2 h 25 min).In other seasons of the year, the general trend continued.However, the minimum period for the onset of vocalization became more shifted from sunset.
In comparison with barking, fox clucking was recorded much less frequently.The cackling of a fox was recorded in the frequency range from 500 to 2500 Hz (Fig. 2).The intervals between individual clucks ranged from 10 to 40 s (28 s on average).The cessation of the vocalization of the fox was noted when the barking of dogs was heard from the nearest village (Fig. 3).Most often, vocalization by red fox were heard from 22:00 to 23:00 (38% of the total daily acoustic activity), from 21:00 to 22:00 (19%).Foxes called somewhat less frequently from 19:00 to 20:00 and from 01:00 to 02:00 (9.5% each).The minimum voice activity was recorded from 17:00 to 19:00, from 20:00 to 21:00, from 23:00 to 01:00 (Fig. 4).

Discussion
According to the literature, the main maximum frequency of different types of fox calls can range from 120 to 2510 Hz [10,11].The maximum fundamental frequency of barking is known to range from 600 to 1200 Hz [11].Darden and Dabelsteen believe that of swift fox (Vulpes velox (Say, 1823)) bark when threatened [12].
Interesting for understanding vocal interaction are the results of scientists in experimental conditions [13].In comparison, the frequency of repetition of fox sounds during vocalization in the natural habitat is more than 2 times lower than that of unselected foxes in terms of behavior under experimental conditions.our results with a few data on the acoustic activity of foxes in other regions, we should highlight a general trend in the timing of vocalization.The vocal variability of foxes has previously been used to identify the main types of sounds [10][11][12]14].They can be divided into several voice types (whining, lowing, clucking, growling and barking) and silent ones (puffing, snorting and coughing).Foxes are known to easily detect a wide range of audio frequencies (from 300 Hz to 34 kHz) and maximize their chances of detecting certain sounds.Foxes are best able to identify the source of a sound between 0.9 and 14 kHz (>90 percent accuracy).They have the greatest difficulty in detecting a sound source at frequencies of 0.3, 0.6, 18, and 34 kHz (≤ 78 percent accuracy) [15].Thus, the absolute hearing sensitivity of the red fox is one of the best among mammals and varies in the range from 51 Hz to 48 kHz [15,16].This is due to the fact that social contacts with the help of sounds for foxes play an important role in their ecology [17].
The vocal activity of the fox for the seasons of the year and individual months is consistent with the frequency of cases of fox infection with rabies in the region [18].Of course, the greatest spring and autumn acoustic activity of the fox and infection with rabies can be explained by the periods of reproduction (rut) and the resettlement of young animals.Thus, bioacoustic methods are and will be effective in studying many aspects of the life of different mammalian species.

Conclusion
The red fox can be classified as a moderately vocalizing mammal.Fox calls were recorded in all seasons of the year, but the most pronounced peaks of prolonged activity in the year were recorded in spring and autumn.March is the most productive month for counting foxes by calls.

Fig. 2 .
Fig. 2. Spectrogram of calls (clucking) by red fox in the vicinity of the village Starye Naimany.

E3SFig. 3 .
Fig. 3. Spectrogram of calls by fox (A) and domestic dog (B) in the vicinity of the village Parakino.