The guanay cormorant (Leucocarbo bougainvilliorum) and red-legged cormorant (Poikilocarbo gaimardi) are known for their prolific nest-building behavior, utilizing a diverse array of materials, including anthropogenic debris, thereby serving as valuable indicators of ocean plastic pollution. To elucidate inter-specific variations in nest plastic occurrence between these two cormorant species, we conducted a comprehensive examination of nests at 12 colonies along the Peruvian coast in 2018–2019. Our findings revealed a significantly higher occurrence of plastic in red-legged cormorant nests (mean 50 ± 27 %, N = 100 nests in 7 colonies) compared to guanay cormorant nests (mean 10 ± 20 %, 3497 nests in 8 colonies). Furthermore, the prevalence of plastic waste varied across colonies within both species. Off-white/clear plastic bags were the predominant color and type of debris found in both cormorant nests. This study is a baseline of plastic marine pollution occurrence along the Peruvian coast. •Plastic debris was found in 10 % and in 50 % of guanay and red-legged cormorant nests, respectively.•The maximum occurrence of plastic debris in the nests varied from 59 % in guanay to 86 % in red-legged cormorants.•The most common type of plastic found in the nests were bags, primarily in off/white/clear, black, and blue/purple colors.•Plastics accounted for a small fraction of the total material weight in guanay cormorant nests (0.04 % - 2.66 %).