Materials & Methods
The CPCV is a 16-km narrow coastal strip located in Lima, Peru, that experiences high traffic of vehicles and people throughout the year. The main characteristics of the CPCV include beaches, parks, sports centers, restaurants, clubs, parking areas located adjacent to the beaches, and infrastructure for pedestrian and vehicular traffic. The highway has two to three lanes designated for vehicular traffic in both directions. The median strip contains public lighting poles and telephone cables that serve as perching sites for neotropic cormorants at four main locations along the highway ( Lozano-Sanllehi & Zavalaga, 2021 ). A total of 1,447 neotropic cormorant pellets were collected from a specific section of this highway (collection started at −12.124764°S, −77.039605°W and ended at −12.122067°S, −77.044313°W, Figure 1 ) in the district of Miraflores between October 27, 2019, and February 28, 2021.

We examined the contents and the frequency of occurrence (%FO) of the pellets to identify plastic and other anthropogenic non-plastic debris before (pre-pandemic) and during (pandemic) the COVID-19 lockdowns in Lima, Peru. Likewise, to determine any changes in diet composition of cormorants between phases, we calculated the relative number of prey items (%NU) for each phase by sorting and counting the otoliths identified to species level in the pellets. Pre-pandemic phase refers to the time before March 16, 2020, when human activities in Peru and the CPCV were not restricted. Throughout the year, people frequented the beaches for leisure, with the highest number of visitors during the austral summer (December–March). Despite the high influx of vehicles and people, neotropic cormorants were regularly seen perching on the light poles and telephone lines ( Majluf, 2014 ; Lozano-Sanllehi & Zavalaga, 2021 ).

Before the pandemic, pellet collection was facilitated by a little wide area in the median strip located in the southern portion of the study area. During the pandemic, the restriction of vehicular circulation also allowed access to other areas along the narrow highway median for pellet collection. However, after the pandemic, the small area designated for pellet collection was closed, and vehicle access to the highway was restored, presenting a challenge to the continuation of pellet collection.

During the pandemic phase, access to the CPCV and nearby beaches was either completely prohibited (full lockdown) or restricted (partial lockdown) for people and vehicles ( Table 1 ). Beaches were entirely off-limits to the public from March 16 to October 22, 2022. However, they were partially accessible from October 23, 2020, until February 28, 2021.

During the pre-pandemic phase (October 2018–February 2020), a total of 11 visits were conducted. On each visit, a minimum of 11 and a maximum of 138 fresh pellets were collected as part of a project monitoring the neotropic cormorant diet. These pellets were stored in a freezer (−40 °C) for subsequent analysis.

During the pandemic phase (July 2020–February 2021) a total of 19 weekly visits were conducted to the study area, with between 11 and 77 fresh pellets being collected during each visit. All pellets were collected during the morning hours to obtain a greater quantity of fresh pellets, which were then individually packaged in 5 × 32 cm paper bags and frozen. Twenty-four hours before analysis, the pellets were defrosted in water and placed on individual Petri dishes. All solid components (such as fish otoliths, vertebrae, shells, plastic, and others) were sorted and allowed to dry at room temperature. In this case, the otoliths found were considered to evaluate the changes and composition in the diet of the cormorants. After the sorting process, the otoliths were further washed and dried to remove any obstructing organic matter or debris. For the identification of the species pertaining to the otoliths we employed the use of the identification guides by Oré-Villalba (2017) and García-Godos (2001) as well as the UIEM (Unidad de Investigación de Ecosistemas Marinos) private otolith collection for reference.

For the plastic debris, if required, a stereoscope (10x magnification) was employed to classify specific plastic debris subcategories, as described by Franeker et al. (2011) :

Sheetlike: Sheets derived from plastic bags.

Threadlike: Filaments like ropes, threads, and plastic fibers.

Fragment: Pieces of plastic objects such as bottles, boxes, toys, and tools.

The plastic debris (>0.1 mm) were measured using a digital caliper (Mitutoyo 150 mm, accuracy 0.1 mm). They were also classified according to their size into microplastics (5 mm), mesoplastics (≥ 5 mm and ≤ 25 mm) and macroplastics (>25 mm). Additionally, non-plastic debris (>0.1 mm) such as glass, metal, paint chips, balloons, and fibers, were also measured in the same manner. All debris were grouped, counted, and separated according to their characteristics.

During each sampling phase, the frequency of occurrence (%FO) of plastic was determined by dividing the count of pellets containing plastic debris by the total number of pellets collected, and then multiplying by 100. In some cases, pellets were collected on different days or weeks within a month. For data analyses, these collections were pooled in a single month. To test for differences in plastic intake by cormorants and prevalence of type of debris before and during the pandemic, a 2 ×2 Chi-square contingency table was used ( Silva-Costa & Bugoni, 2013 ). Additionally, the average litter load in pellets was calculated by dividing the number of anthropogenic items found per month by the total number of pellets found per month. This approach facilitated the reporting of the average loads of plastic and other anthropogenic materials to determine if these loads also vary with lockdown levels. The Mann–Whitney U test was used to compare the litter load per pellet between phases as data distribution did not follow the normality criteria (Shapiro–Wilks, W = 0.564, P < 0.0001). Changes in diet composition were tested with a paired t -test by comparing the %NU of the main prey.

All field procedures were ethically approved by the committee of ethics Universidad Cientifica del Sur (Constancia N ∘ 057-CIEI-AB-CIENTÍFICA-2021).