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.
Andreychev A. Vocalizations by red fox (Vulpes vulpes) in natural and climatic conditions of Mordovia (Middle Volga region)// E3S Web of Conferences 462, 01004 (2023).

We recorded vocal interaction in the natural environment of an Eurasian Eagle-Owl (Bubo bubo) with canines Gray Wolves (Canis lupus), Red Foxes (Vulpes vulpes) and domestic dogs (Canis familiaris). Vocalization was recorded using Olympus digital voice recorders. The calls of the male Eurasian Eagle-Owl were recorded by us in the frequency range of 200–420 Hz. The howl of a Gray Wolf was recorded in the frequency range from 300 to 1,100 Hz. Red Fox barking was recorded in the frequency range from 750 to 1,000 Hz. Barking of domestic dogs was recorded in the frequency range from 250 to 1,500 Hz. The vocalization of the Eurasian Eagle-Owl had an independent character inherent in the biology of the species. The Eurasian Eagle-Owl, with its cries, involuntarily provoked the entry of canines into joint vocal interaction, which can be explained by the high social activity of the latter. Co-vocalizations of the Eurasian Eagle-Owl and canines were noted in winter, spring and autumn, but mainly in spring (50%). The increased use of autonomous voice recorders, which record spontaneous vocalizations emitted by animals over long periods, will allow us to better document and study the importance of such interspecific interactions.
Andreychev A. Vocal interaction between Eagle Owl (Bubo bubo) and canines (Carnivora, Canidae) // Ornis Hungarica. 2023. V. 31. № 2. P. 61–73.

Предложен новый метод регистрации филина по акустическим сигналам с использованием цифровых портативных диктофонов. Диктофон позволяет записывать голосовую активность крупной совы на расстоянии до 4 км от места установки до кричащей птицы в зависимости от направления и скорости ветра, а также рельефа местности. Время непрерывной работы диктофона от одного комплекта внешних алкалиновых батарей составляет около 140 ч. Метод апробирован в условиях лесостепной зоны Поволжья. С его помощью на предварительном этапе только за один год выявлено 7 новых гнезд и дополнительно 17 гнездовых участков. При этом применявшиеся ранее (2008-2014 гг.) методы пеленгации и прочесывания местности позволили обнаружить только 6 гнезд. Преимущества предложенного метода заключаются в охвате больших территорий и экономии времени.
Андрейчев А.В., Лапшин А.С., Кузнецов В.А. Методика регистрации филина (Bubo bubo) по голосовой активности // Зоологический журнал. 2017. Т. 96. № 5. С. 601–605.