The influence of egg presence and eggshell colour in the attraction of visually oriented predators to nests of a tropical forest bird

Abstract

Several hypotheses have been proposed to account for the function of eggshell pigmentation. One predicts that patterns of colour and markings provide camouflage against visually oriented nest predators. However, the effectiveness of any anti‐predatory function of eggshell colour may be reduced if predators can use the nests per se as foraging cues (nest‐crypsis hypothesis). Here, we tested whether eggshell pigmentation, and a set of concurrent variables, could explain nest predation in natural nests of the Atlantic Forest endemic Blue Manakin Chiroxiphia caudata containing plasticine eggs. Nests were continuously monitored for predator identification using infra‐red camera traps, and we considered the nest‐crypsis hypothesis by testing the premise that if predators can use nests as visual cues, they would be recorded checking empty nests at rates similar to those containing eggs. Six bird species were identified as visually oriented predators of nest contents, and predation frequencies were low and not influenced by eggshell colour. Empty nests and nests containing eggs were visited by predators at similar frequencies, independently of eggshell colour, which provided the first direct support for the nest‐crypsis hypothesis. It suggests that for this tropical forest, open‐nesting passerine, selective forces driving nest concealment and nest camouflage may be stronger than selection for eggshell colour variation.

Massive Bird Nest Losses: A Neglected Threat for Passerine Birds in Atlantic Forest Fragments from the Pernambuco Endemism Center

“…Notably, the critically endangered white-collared kite Leptodon forbesi was filmed checking a nest that was already depredated by marmosets. Checking empty nests reveal a certain level of specialization, since the predator was capable of recognizing the nest per se as a source of food, even without eye contact with eggs or nestlings [58]. At the Carlos Botelho State Park, in southeastern Brazil, the white-necked hawk Amadonastur lacernulatus was an important nest predator [33], evidencing that the rare L. forbesi could have been a potential nest predator in the PEC that had its abundance drastically affected by habitat loss and fragmentation, as today, it is one of the most threatened birds of prey on earth [22].…”

Mixed evidence for nest masquerading in the Blue Manakin (Chiroxiphia caudata)

“…Second, toucans were the main nest predators, and in a recent work we demonstrated that in the sequence of events that precede nest predation, these birds can use the nests per se as search images (Zima et al . 2021). It is therefore possible that toucans, and other visually oriented predators, could have learned how to use the agglomerates of pendent mosses and debris as cues to find the Blue Manakin nests, i.e.…”

“…2020 and Zima et al . 2021 for methodological details), and forest canopy cover was estimated using a spherical densiometer (Convex Model‐A; Forest Suppliers, Inc., Jackson, MS, USA) following the manufacturer's instructions (Lemmon 1956).…”

“…Here we used the same set of Blue Manakin nests to look for evidence of nest masquerading, focusing on potential interactions between nests and visually oriented nest predators, which in the study area are other birds (Ribeiro-Silva et al 2018, Perrella et al 2020. For details on the study area and nest search procedures, see Perrella et al (2020) and Zima et al (2021).…”

“…We did not consider this a problem because the outer walls of Blue Manakin nests also varied in the relative amounts of these materials. Vegetation density was estimated within a 50-cm radius (see Perrella et al 2020 andZima et al 2021 for methodological details), and forest canopy cover was estimated using a spherical densiometer (Convex Model-A; Forest Suppliers, Inc., Jackson, MS, USA) following the manufacturer's instructions (Lemmon 1956).…”