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Keast, A. (1965). Interrelationship of two zebra species in an overlap zone. J Mammal, 46(1), 53–65.
Abstract: The distinctive Somali Arid and the East African grassland faunas approach each other to the north of the Kenya Highlands and along the Tana River. Both have unique endemics and many counterparts at the species and race level. Mostly these latter remain isolated but there are instances of intergradation and range overlap without interbreeding. An interesting case of the latter, that of the zebras Equus grevyi and E. burchelli, is analyzed here. The unusual feature of the zebra overlap is that mixed herds are formed. These maintain a level of constancy from day to day, and are not disrupted during flight. Mutual tolerance is marked. While mixed herds occur all year, the composition varies from season to season and district to district. Migrations may take place conjointly. Outside of the overlap zone habitat differences are marked. The mixed zebra herds of Kenya are contrasted with the zebra-wildebeest associations of the Kruger Park, South Africa, and it is shown that the former have greater cohesion and constanc
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Pluhácek, j., Bartos, L., & Víchová, J. (2006). Variation In Incidence Of Male Infanticide Within Subspecies Of Plains Zebra (Equus Burchelli). Journal of Mammalogy, 87(1), 35–40.
Abstract: Social organization seems to determine the occurrence of male infanticide in equids. Although, no information concerning social organization of the maneless zebra (Equus burchelli borensis) has been available, we presumed that the occurrence of infanticide would be the same across all subspecies of plains zebra. We examined the occurrence of this phenomenon in 9 herds of 4 subspecies: the maneless zebra, Grant's zebra (E. burchelli boehmi), Chapmann's zebra (E. b. chapmanni), and the Damara zebra (E. b. antiquorum) at 4 zoos. The probability of a foal's death was affected by the presence of a new male and subspecies. Except for the maneless zebra, all subspecies showed existence of male infanticide. We found no occurrence of male infanticide in maneless zebras, which suggests a different social system. This would also support the subspecific status of the maneless zebra.
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Berger J. (1985). Interspecific Interactions and Dominance among Wild Great Basin Ungulates. J. Mamm., 66(3), . 571–573.
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Pacheco, M. A., & Herrera, E. A. (1977). Social Structure of Feral Horses in the Llanos of Venezuela. J Mammal, 78(1), 15–22.
Abstract: Feral horses (Equus caballus) in the Venezuelan savannas (Ilanos) formed bands of 3-35 individuals; mean group size varied between 15 and 21. Some bands had up to three adult males, and there was a positive correlation between the number of males and the number of females in bands. Adult males also were seen solitary or formed bachelor groups. One association of three females was observed for 3 months. We noted a correlation between number of females in bands and number of foals per female born during our study (January-July 1992). The advantages of being in larger groups were unclear, because natural predators were rare. Perhaps females in larger groups have more time available for foraging due to reduced individual vigilance or that larger groups live in better-quality home ranges.
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Passilongo, D., Marchetto, M., & Apollonio, M. (2017). Singing in a wolf chorus: structure and complexity of a multicomponent acoustic behaviour. Hysterix, 28(2), 180–185.
Abstract: Wolf choruses ( Canis lupus ) are complex, multicomponent signals, composed by a series of different vocalizations emitted by a pack. Although howls, the main component, have been highly studied, poor attention has been drawn upon the other vocalizations of the chorus. In this study, we investigate the structure of the chorus by means of the analysis and the quantification of the different components, taking advantage both of the digital sound recording and analysis, and of the modern statistical methodologies. We provide for the first time a detailed, objective description of the types of call emitted during the wolf howlings, combining spectrographic examinations, spectral analyses and automated classifications, with the aim to identify different types of call. Our results show that wolf choruses have a rich, complex structure, that reveals six other types of call, to be added to those howls already described in literature. Wolf choruses are typically composed by other three different types of calls: the bark, i.e. relatively long calls characterized by low frequencies and the presence of harsh components (deterministic chaos); the whimper, characterized by a harmonic structure and a very short duration; and the growl, a call with a noisy structure, low frequencies but relative long duration. Although further investigations are necessary to understand the meaning of the different calls, this research provides a basis for those studies that aim to compare wolves and other canids vocal behaviour.
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