This paper explores the potential signatures of ultralight bosons in the orbital eccentricity of binary black holes (BBHs) through gravitational wave (GW) observations. The authors show that the presence of ultralight boson clouds around black holes during their cosmological evolution can leave a measurable imprint on the distribution of masses and orbital eccentricities observed by future GW detectors. For nonprecessing BBHs with chirp masses $ M \lesssim 10 M_{\odot} $, formed in isolation, larger-than-expected eccentricities $ e \gtrsim 10^{-2} $ at GW frequencies $ f_{GW} \simeq 10^{-2} $ Hz could indicate the presence of ultralight bosons with masses in the range $ [0.5, 2.5] \times 10^{-12} $ eV. These bosons, formed via superradiance instabilities, can produce a large backreaction on the orbital evolution, leading to sharp features in the dynamics of BBHs, such as Landau-Zener (LZ) resonances and ionization effects. The presence of such clouds can significantly affect the in-band phase evolution and peak frequency of GW signals, providing unique signatures of ultralight bosons in BBH dynamics. These effects are expected to be detectable by future detectors such as LISA, mid-band, and Deci-hertz detectors. The paper also discusses the implications of these findings for the formation channels of BBHs and the potential for detecting ultralight bosons through their influence on the eccentricity of BBH mergers. The results suggest that the presence of ultralight bosons could lead to a skewed correlation between the masses and eccentricities of BBHs, with a significant fraction of BBHs undergoing a rapid growth of orbital eccentricity to a critical value. The paper further explores the implications of these findings for the detection of ultralight bosons through their influence on the eccentricity of BBH mergers, and the potential for these effects to be observed by future GW detectors.This paper explores the potential signatures of ultralight bosons in the orbital eccentricity of binary black holes (BBHs) through gravitational wave (GW) observations. The authors show that the presence of ultralight boson clouds around black holes during their cosmological evolution can leave a measurable imprint on the distribution of masses and orbital eccentricities observed by future GW detectors. For nonprecessing BBHs with chirp masses $ M \lesssim 10 M_{\odot} $, formed in isolation, larger-than-expected eccentricities $ e \gtrsim 10^{-2} $ at GW frequencies $ f_{GW} \simeq 10^{-2} $ Hz could indicate the presence of ultralight bosons with masses in the range $ [0.5, 2.5] \times 10^{-12} $ eV. These bosons, formed via superradiance instabilities, can produce a large backreaction on the orbital evolution, leading to sharp features in the dynamics of BBHs, such as Landau-Zener (LZ) resonances and ionization effects. The presence of such clouds can significantly affect the in-band phase evolution and peak frequency of GW signals, providing unique signatures of ultralight bosons in BBH dynamics. These effects are expected to be detectable by future detectors such as LISA, mid-band, and Deci-hertz detectors. The paper also discusses the implications of these findings for the formation channels of BBHs and the potential for detecting ultralight bosons through their influence on the eccentricity of BBH mergers. The results suggest that the presence of ultralight bosons could lead to a skewed correlation between the masses and eccentricities of BBHs, with a significant fraction of BBHs undergoing a rapid growth of orbital eccentricity to a critical value. The paper further explores the implications of these findings for the detection of ultralight bosons through their influence on the eccentricity of BBH mergers, and the potential for these effects to be observed by future GW detectors.