We consider the long-time evolution of weakly perturbed discrete nonlinear Schrödinger breathers. While breather growth can occur through nonlinear interaction with one single initial linear mode, breather decay is found to require excitation of at least two independent modes. All growth and decay processes of lowest order are found to disappear for breathers larger than a threshold value.PACS numbers: 63.20. Pw, 45.05.+x, 42.65.Tg The study of intrinsically localized modes in anharmonic lattices, discrete breathers, has yielded much attention during the last decade (see e.g. [1,2]). In particular, their existence as time-periodic solutions of nonlinear lattice-equations was proven under quite general conditions [3], and numerical schemes were developed for their explicit calculation [4]. The generality of the concept of discrete breathers, which provide very efficient means to localize energy, has lead to numerous suggestions to its application in contexts where anharmonicity and discreteness are important, e.g. for describing energy and charge transport and storage in biological macromolecules [5]. Recently, discrete breathers have been experimentally observed in coupled optical waveguides [6], in charge-density wave systems [7], in magnetic systems [8], and in arrays of coupled Josephson junctions [9].Although a discrete breather under quite general conditions is linearly stable [1,3,10] (and thus no perturbations grow exponentially), there are many questions remaining concerning the long-time fate of perturbed breathers. In a previous paper [11], some of these questions were addressed considering a particular model, the discrete nonlinear Schrödinger (DNLS) equation. The interaction between stationary breathers and small perturbations corresponding to time-periodic eigensolutions to the linearized equations of motion around the breather was investigated using a multiscale perturbational approach, and it was found that the nonlinear interaction between the breather and single-mode small-amplitude perturbations could lead to breather growth through generation of radiating higher harmonics, but not to breather decay. It is the purpose of this Report to extend these results to more general perturbations of stationary DNLS breathers. In particular, we find that while the simplest growth process can be described as an inelastic scattering process with a one-frequency incoming wave and an additional outgoing higher-harmonic wave, the description of a decay process requires at least two incoming modes yielding outgoing modes with frequencies being linear combinations of the original ones.In order to make this Report self-contained, we first recapitulate the main formalism from [11] (to which the reader is referred for details; see also [12] for a similar approach in continuous NLS models). With canonical conjugated variables {iψ n }, {ψ * n }, the DNLS equation can be derived from the Hamiltonian H ({iψ n } , {ψ * n }) = n