  (abridged) The work studies active star formation (SF) and a possible trigger
of SF bursts due to gravitational interaction. Following the study by Taylor et
al. we extend the search for possible disturbing galaxies of various masses to
a much larger sample of 86 BCGs from the sky region of Second Byurakan survey.
The sample under study is separated by the criteria: EW([O III]5007 > 45 A and
V < 6,000 km/s and should be representative of all low-mass galaxies which
experience SF bursts. We argue that the moderate tidal disturbers should be
taken into account, and incorporate the respective range of distances in the
search for disturbing neighbours. The majority of the neighbours in the
vicinity of the studied BCGs are found through the study of their environment
among UZC galaxies, and the follow-up careful search of the fainter galaxies in
the NED database. For the remaining BCGs, the neighbouring galaxies are found
based on the results of the 6-m telescope spectroscopy. By studing the data on
the radial velocities of galaxies in the vicinity of BCGs we found: 1) 33 of
the studied BCGs (38.5 %) are associated with significantly brighter galaxies
(DB > 1.5 mag); 2) 23 BCGs (26.5%) have neighbours either of comparable or
significantly lower brightness; 3) 14 of the studied BCGs (16%) with no evident
associated galaxy are either certain, or probable, mergers. We conclude that in
\~80% (or more) BCGs from the studied sample, the SF bursts are triggered
either by tidal action of various strengths from other galaxies, or due to
mergers of low-mass galaxies. We briefly discuss the implications of our main
conclusion for evolutionary links of BCGs to other types of low-mass galaxies.
Among the ``isolated'' BCGs (without a bright neighbour) 43+-10% are probably
disturbed by dwarf galaxies and 26+-8% have a merger morphology.
