This study used the Developmental Niche (DN) framework to examine perceived intergenerational changes in the transmission of Traditional Ecological Knowledge (TEK). Under a cross-sectional and exploratory design, in-depth semi-structured interviews were conducted with a purposeful sample, stratified by gender and generation, of 30 Uitoto (Amazon, Colombia) and 26 Itza' Maya (Peten, Guatemala) adults about their perceptions of intergenerational variations in TEK transmission/acquisition practices. Interview data were analyzed using a grounded approach and resulting coding categories were assigned to text units. Grounded themes were then examined in light of the DN components. Both Uitoto and Itza' Maya participants perceived generational changes in the settings (from natural to school settings) and in the strategies (from experiential to conceptual learning) used for TEK transmission. These changes were attributed to various environmental (biodiversity loss, urbanization), socio-cultural (acculturation, changes in social norms) and individual factors (lack of motivation to teach and learn).