Causes and Consequences of Nest Mass and Structure Variation in the Bay-Capped Wren-SpinetailSpartonoica maluroides

Abstract

Bay-capped Wren-Spinetail Spartonoica maluroides (Furnariidae) nests very close to the ground in dense clumps of grasses or sedges and builds both open and enclosed nest. We describe a proportion and characteristics of both types of nests and evaluate some causes that could force the construction of one nest architecture or another. In order to study the causes of this variation, we assessed the variability of nest types (architecture and size) and vegetation structure, and examined their consequences for breeding parameters in a population of Bay-capped Wren-Spinetail breeding in Spartina densiflora saltmarshes located at a coastal lagoon on Atlantic coast in east Argentina. We found that Bay-capped Wren-Spinetail builds nests enclosed and open with similar frequency within the same population and vegetation type. All nests were built with stems and grass leaves of S. densiflora. We found that open nests were built in sites with denser vegetation than enclosed nests. Nesting success and nest survival were not affected by nest architecture and size. The ability to adjust nest structure according to the vegetation density may be a strategy aimed at increasing nest concealment to reduce the temperature inside the nest or to avoid nest depredation. A flexible nest architecture strategy in Bay-capped Wren-spinetail is a possible adaptation to living in simple, yet structurally variable environments such as saltmarshes.

Climate as an Evolutionary Driver of Nest Morphology in Birds: A Review

“…Among species that build a nest structure, the presence or absence of a roof, or whether or not, it is placed in a cavity, can have large effects on the thermal performance (Griffith et al, 2016), leading to the expectation of intraspecific variation in nest shape in species with wide geographic ranges. It is puzzling that within-species, the potential to dramatically alter nest shape (e.g., from cup to domed or vice versa) appears to be rare (Cardoni et al, 2017). It is possible that general nest shape is already well adapted to environmental conditions in the species' current distribution, such that variation at this level is unnecessary at smaller taxonomic scales.…”

“…One example is the golden-headed cisticola (Cisticola exilis), which is described as having open cup nests in some parts of its distribution in NE India and domed nests in other parts (Del Hoyo et al, 2017), but the causes for these differences are unknown. Another interesting case is that of the baycapped wren-spinetail (Spartonoica maluroides), which builds two different nest types in the same region in Argentina, but the causes for such variation are not completely clear either (Cardoni et al, 2017). These systems might be ideal to investigate the role of climate in driving intraspecific nest variation at broader scales.…”

Sexual Dimorphism and Parental Care in the Wren-Like Rushbird Phleocryptes melanops

“…Immediately after capture, we measured and ringed each individual with a unique combination of two coloured plastic bands (rings). We measured characters that are commonly used for determining sexual dimorphism in other bird species (Winker et al ., 1994; Moreno et al ., 2007; Cardoni et al ., 2009): bill length, taken from the anterior point of the nostril to the bill tip; bill width, taken across the bill base under the proximal point of the nostrils; bill depth, taken at the anterior point of the nostrils; tarsus length, taken from the joint of the tibiotarsus and tarsometatarsus to the distal edge of the most distal unbroken scute overlying the middle toe; tail length, taken between the two middle tail feathers, from the base of the feathers to the end of the longest feather; wing chord, taken from the carpal joint to the tip of the longest primary. We used a digital caliper (± 0.01mm) for bill and tarsus measurements and a ruler (± 1mm) for tail and wing measurements.…”

“…Sexual dimorphism in size is also slight. The few detailed studies have revealed that males are slightly larger than females in linear measurements (e.g., Winker et al ., 1994; Remsen, 2003; Moreno et al ., 2007; Cardoni et al ., 2009), which is in accordance with the presumed social monogamy of many species and the apparent similar role of both sexes in parental care. The few existing studies have reported that both members of the pair contribute to nest-building, incubation, and feeding of nestlings and fledglings (Kendeigh, 1952; Nores & Nores, 1994; Skutch, 1996; Moreno et al ., 2007; Massoni et al ., 2012).…”

The Impact of Weather on the Behavior and Ecology of Birds

“…Among species that build a nest structure, the presence or absence of a roof, or whether or not, it is placed in a cavity, can have large effects on the thermal performance , leading to the expectation of intraspecific variation in nest shape in species with wide geographic ranges. It is puzzling that within-species, the potential to dramatically alter nest shape (e.g., from cup to domed or vice versa) appears to be rare (Cardoni et al, 2017). It is possible that general nest shape is already well adapted to environmental conditions in the species' current distribution, such that variation at this level is unnecessary at smaller taxonomic scales.…”