Capsule: Studies of nest predation using artificial nests need to consider the effect of egg size on the types of predator that are detected. Aims: To estimate the nest predation rate in the Patagonian temperate forest and evaluate the influence of egg size on predator guild. Methods: On different plant species, we placed 108 nests each containing eggs of either Atlantic Canary Serinus canaria or Common Quail Coturnix coturnix, and a model clay egg of equal size to the real egg. Nest predators were identified from the marks left on the clay eggs or by videos recorded using camera traps. Results: 86% of the nests were predated. Birds, mainly Chimango Caracara Milvago chimango, were the main nest predators. A marsupial, the Monito del Monte Dromiciops gliroides, and rodents also contributed to nest predation. Nest predation rates were similar for both egg sizes but the nest predator guild was different. Birds and rodents preyed on both eggs but the Monito del Monte consumed mainly small eggs. Conclusion: Egg size did not influence the rate of nest predation but, instead, affected the nest predator guild. Consequently, in order to avoid underestimating the impacts of small predators, egg size should be considered in studies of nest predation.

Deer abundance and occupancy areas are currently increasing worldwide, with unknown consequences for birds. Deer impacts on birds have mainly been assumed to be indirect through mechanisms that negatively influence vegetation complexity and reduce habitat quality. Information on the direct negative impacts on bird breeding success is scattered and rudimentary. Here we documented, through videos filmed with camera traps, non‐native deer preying on bird nests. We supported this finding by investigating nest predator behaviour in other areas of the world both in the scientific literature and audio‐visual platforms. We suggest that our scientific naturalist records and the collected information might reflect poorly understood deer behaviour, in both native and non‐native populations. In areas with a high number of individuals, nest predation by deer could have severe consequences for native birds, causing serious alterations in their breeding biology. Future studies are needed to address questions about the consequences of an increase in deer density on avian populations.