Giant Wrens nesting in a plastic bag

While watching a pair of Giant Wrens / Riesenzaunkönige (Campylorhynchus chiapensis) along a sandy track through banana plantations just south of Los Limones, Dep. San Marcos, Guatemala on 12 February 2023 with Ana Paula Oxom, we noted that the birds were collecting nesting material (dry leaves, vines, grass, sticks, feathers) from the track. They then flew into the banana plantations, where we soon found the surprising nest site. The pair had chosen one of the blue polyethylene bags that are used to protect the growing bananas, 3 meters above the ground.

The innovation is attributed to Carlos Gonzales Fajardo in 1956 in Guatemala. The practice has since spread to all export [banana] plantations and is considered essential to increase yield and improve fruit quality. The cover creates a  microclimate that maintains a high temperature and prevents chill damage. Depending on the study, the temperature over a 24-hour period increases on average by 0.5°C inside the cover and can increase by 7°C in the warmest hours.

https://www.promusa.org/Bagging

The birds approached the nest in low flight, first perched on a concrete fence post just below the bananas (see photos) and then entered the bag, which has an opening facing the ground, with a short, vertical flight. The globular nest was built with the green bananas serving as the supporting structure.

There’s very little information on nesting behavior of Giant Wren in the literature (and none at all from Guatemala), the most comprehensive being the species account at birdsoftheworld.org (Kroodsma & Brewer 2020) which is mostly based on the observations of Alexander F. Skutch (1960, 1976). Kroodsma & Brewer state the breeding season to be „May-July“, which is in contrast to this nest-building observation from mid-February.