Abstract
Substrate type is a key-factor in nest-site selection and nest architecture of burrowing birds. However, little is known about which factors drive nest-site selection for these species, especially in the tropics. We studied the influence of soil attributes on nest-site selection by the campo miner Geositta poeciloptera, an open grassland bird that builds its nests within soil cavities. For all nests found, we measured the depth of the nest cavity and the resistance of the soil to penetration, and identified the soil horizon in which the nest was located. In soil banks with nests, we collected soil samples for granulometric analysis around each nest cavity, while in soil banks without nests we collected these samples at random points. From 43 nests found, 86% were located in the deeper soil horizons (C-horizon), and only 14% in the shallower horizons (B-horizon). Granulometric analysis showed that the C-horizons possessed a high similar granulometric composition, with high silt and low clay contents. These characteristics are associated with a low degree of structural development of the soil, which makes it easier to excavate. Contrarily, soil resistance to penetration does not seem to be an important criterion for nest site selection, although nests in more resistant the soils tend to have shallower nest cavities. Among the soil banks analyzed, 40% of those without cavities possessed a larger proportion of B-horizon relative to the C-horizon, and their texture was more clayey. On the other hand, almost all soil banks containing nest cavities had a larger C-horizon and a silty texture, indicating that soil attributes drive nest-site selection by G. poeciloptera. Thus, we conclude that the patchy distribution of G. poeciloptera can attributed to the infrequent natural exposure of the C-horizon in the tropical region, where well developed, deep and permeable soils are more common.
Highlights
Birds select nest-sites by assessing many biotic and abiotic environmental factors (e.g., [1,2,3,4,5])
We aimed to answer the following three questions: 1) Is cavity depth influenced by soil resistance to penetration? 2) Are soil resistance to penetration and/or soil horizon type driving nest location in steep soil banks? and 3) Which soil attributes better predict the presence or absence of nests in a given steep soil bank? For the first question, we hypothesize that more resistant soils will have shallower nests
The study was conducted in the municipality of São João del-Rei, which is located in the northern portion of Upper Rio Grande Grasslands (URGG), in the southern part of the state of Minas Gerais, Brazil (~21 ̊29’–21 ̊32’S; 43 ̊50’–44 ̊55’W) (Fig 2)
Summary
Birds select nest-sites by assessing many biotic and abiotic environmental factors (e.g., [1,2,3,4,5]). The type of substrate chosen for nest construction is . The attributes of the substrate that drive nest-site selection are still poorly studied for excavating birds, even though the first observations on the subject were published decades ago [9,10,11]. For birds that construct their nests within soil cavities, the granulometric composition of the soil—which is related to the ease of excavation—is an important factor that can even determine the geographic distribution of a species [12]
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