Strange nucleon form factors with $N_f=2+1$ O($a$)-improved Wilson fermions

We present preliminary results for strangeness form factors of the nucleon computed on the CLS ensembles with $N_f=2+1$ flavors of O($a$)-improved Wilson fermions. Our calculations are performed at two values of the lattice spacing ($a\in \{0.064,0.086\}\mathrm{f}\mathrm{m}$) and three values of the pion mass ($m_{\pi }\in \{200,280,340\}\mathrm{M}\mathrm{e}\mathrm{V}$). The determination of strangeness form factors proceeds by computing quark-disconnected diagrams, for which we employ hierarchical probing in four dimensions in order to deal with this most challenging part of the calculation. Furthermore, we investigate several source-sink separations to check for excited-state contamination.