On the use of anthropogenic materials in nest building of House Wren (Troglodytes aedon), a report from Parque Los Algarrobos, Cumbayá, Ecuador

Nests are structures built by a variety of vertebrates and often control the conditions where offspring develop [1,2,3]. Nesting materials often vary but can cause differing effects based on the emerging properties of the material. Such effects can change the nest’s insulation, antimicrobial and antiparasitic properties, concealment, and even the owner’s capacity for attracting mates [4].

Due to increasing human populations, anthropogenic environments are continuously replacing native ecosystems [5]. This loss of natural environments has caused various biotic and abiotic effects on native ecosystems. Human behaviors frequently impact both the natural areas adjacent to human settlements and the organisms residing in these areas. Numerous bird species incorporate anthropogenic material into their nests due to growing availability of pollutants globally [6]. The prevalence and type of anthropogenic nest materials (ANMs) used vary depending on availability; however, they can also depend on the preference of species or other variables [7].

Plenty of research has been done on the use of ANMs by seabirds [8,9,10,11,12,13]. However, terrestrial birds may have a higher amount of ANMs incorporated in their nests [6]. Numerous terrestrial birds, particularly passerine birds, have been found to use ANMs [14,15,16,17,18,19,20,21,22,23,24,25,26,27]. These behaviors occur in a variety of families within the order Passeriformes; nevertheless, the inclusion of ANMs in wrens of the family Troglodytidae has seldom been reported [28,29]. Likewise, in Latin America, these types of ecological records are rarely published. Despite its high biodiversity, the field of ecology of this region amounts to merely 9% of worldwide publications [30].

Troglodytes aedon (Vieillot, 1809) is a passerine bird belonging to the family Troglodytidae. Widely distributed, this species inhabits a vast range throughout the Americas, from southern Canada to the southernmost point of Argentina [31,32]. It exhibits a preference for habitats such as inter-Andean valleys and often coexists with human populations in various ecosystems [33,34,35,36]. In these areas, it is uncertain how urban anthropogenic disturbance affects the House Wren’s ecological behaviors, like singing, diet, predation, or nesting [37,38,39,40]. In this paper, we document the use of ANMs by a House Wren (Troglodytes aedon).

On November 26, 2023, at 11:11 am, we observed for ~20 min and photographed one individual House Wren at the lookout located at the entrance of Parque Los Algarrobos in Cumbayá, Pichincha Province, Ecuador (-0.206636, -78.420660, WGS84). This individual was observed carrying a piece of transparent plastic in its beak (see Fig 1). The plastic material appeared to be from an aged clear wrapper or plastic bag with an elongated shape. The House Wren was identified following the Fieldbook of the Birds of Ecuador [41], based on its striped, brown coloration and pale-brown venter as diagnostic features.

The House Wren was initially spotted on the branches of a castor bean plant (Ricinus communis), approximately 7 m from the outlook towards the metropolitan park (Fig. 1A). From there, it traversed from branch to branch into a chilca plant (Baccharis latifolia) (Fig. 1B) and subsequently flew towards a streetlamp on the deck structure of the viewpoint. Entering the lamp (Fig. 1C), it reemerged about 1 min later without the piece of plastic. The wren then vocalized for about 2 min (Fig. 1D), positioned itself on top of the lamp post, and continued vocalizing (see Fig. 1E); this behavior persisted for approximately 10 min.

Figure 1
A House Wren holding a piece of plastic on a Castor Bean plant B House Wren holding the piece of plastic on a chilca plant C House Wren entering streetlampnest with the piece of plastic D House Wren emerging from the streetlamp without the piece of plastic and vocalizing E House Wren on top of the streetlamp post vocalizing

The observation of a House Wren individual incorporating ANMs into its nest raises intriguing questions about the factors influencing the use of these nest materials by urban land birds. In temperate areas, House Wren nesting is well documented. These reports include the use of artificial structures in disturbed areas and the occasional use of ANMs. Reported elements used to build nests include hanging sacks, oil cans, animal skulls, wooden beams, etc. [36,41,42,43]. This variety of materials demonstrates the species’ adaptability to withstand human changes and environments but does not imply clear preferences for any element.

Five hypotheses have been proposed to explain the use of ANMs for birds in urban areas. (1) The Availability Hypothesis argues that the most common materials in the environment are going to be incorporated into nests, and thus the reduction of native plants in nesting areas can lead to the increase of ANMs due to their functional resemblance to natural nesting material [27,44,45]. (2) The Age Hypothesis states that

in urban areas, where birds tend to reach older ages, experienced (older) birds may use more ANMs due to their known resemblance to native materials [44,45,46,47]. (3) The New Location Hypothesis posits that novel nesting sites, such as buildings or nest boxes, challenge birds to acquire new nesting materials such as ANMs [45,48,49,50]. (4) The Adaptive Hypothesis posits that alterations in nest building materials and behavior stem from their adaptive value, with novel materials chosen for intrinsic benefits like antimicrobial activity or versatility [51,52,53,54]. Additionally, within this hypothesis, sexual selection may contribute, as suggested by the (5) Signaling Hypothesis, which proposes that as an extended phenotype, birds utilize ANMs to indicate reproductive quality through nest building [55,56,57].

The observed behavior seems to align with various of these hypotheses. However, we lean toward the Availability Hypothesis, which suggests that the scarcity of native plants may drive House Wrens to incorporate ANMs. The transparent plastic used by the House Wren, resembling natural materials with its elongated shape, might serve as an alternative amidst diminishing native resources. Additionally, the use of a streetlamp as a nesting structure could support the New Location Hypothesis, indicating the House Wrens’ adaptation to unconventional nesting sites. Another intriguing possibility is that the observed behavior aligns with the Signaling Hypothesis. The vocalization of the male House Wren during nest building suggests a potential attraction mechanism, intertwining nest construction and mate attraction. The interplay of various factors from these hypotheses adds complexity to our understanding of the observed behavior.

In conclusion, this observation provides insights into the complex interplay of factors influencing avian nest-building behaviors in urban environments. Further studies are warranted to explore the prevalence of ANMs in wren nests and to unravel the underlying mechanisms and adaptive significance of such behaviors. Understanding these dynamics is crucial for the effective conservation and management of urban bird populations in the face of ongoing environmental changes and human population growth.

We express our gratitude to everyone who participated in the “Gran Bioblitz del Sur” for their valuable assistance and participation in the event. Special thanks to the Laboratorio de Zoología Terrestre and the Museo de Zoología ZSFQ, within the Instituto de Biodiversidad Tropical IBIOTROP, at Universidad San Francisco de Quito USFQ, for their support in organizing such events and fostering our curiosity, enabling us to share this valuable information. Additionally, we extend our appreciation to Elisa Bonaccorso and the anonymous reviewers for their valuable suggestions on this manuscript.

Mateo Dávila-Játiva, Roberto J. León-E., and Ariel Guerrero-Campoverde spotted the nest building event together and contributed to the writing of the manuscript. Mateo Dávila-Játiva took the pictures and prepared the figure.