  We investigate the relationship between three natural invariants of complex
hyperbolic disc orbibundles over oriented and closed hyperbolic $2$-orbifolds.
These invariants are the Euler characteristic $\chi$ of the $2$-orbifold, the
Euler number $e$ of the disc orbibundle, and the Toledo invariant $\tau$ of a
faithful representation of the surface group into $\mathrm{PU}(2,1)$ attached
to the complex hyperbolic structure of the disc orbibundle. Based on previous
examples, we conjecture that $-3|\tau| = 2e+2\chi$ always holds. For complex
hyperbolic disc orbibundles over $2$-orbifolds derived from quadrangles of
bisectors via tessellation, we prove that $3\tau = 2e+2\chi$. Furthermore, we
demonstrate that $-3|\tau| = 2e+2\chi$ holds when a section with no complex
tangent planes is present.
