Tree cavity density is a limiting factor for a secondary cavity nester in second-growth Andean temperate rainforests

Cavity-nesting bird populations are most frequently limited by the number of tree cavities available in second-growth forests. However, this possible limitation of a key resource is less clear in old-growth forests. We compared forest attributes (i.e., basal area, density of larger trees, density of dead trees, and tree cavity density) in second-growth and old-growth stands in Andean temperate rainforests in southern Chile. To examine the role of nest-site availability in limiting the populations of Thorn-Tailed Rayaditos (Aphrastura spinicauda), a secondary cavity-nesting bird species, we conducted an experiment in which nest-boxes were added and removed in old-growth and second-growth forests during a five-year period (2008-2013). In old-growth forests, as compared to second-growth forests, we found a more than double basal area (99.6 vs. 43.7 m2/ha), a three times higher density of larger trees (88.2 vs. 36.4 trees/ha), and a 1.5 times higher number of small cavities (25.9 vs. 10.3 c..., Study area
We studied a small bodied secondary cavity-nesting bird species in Andean temperate rainforests of southern Chile (Thorn-Tailed Rayadito, 11.74 g; Altamirano et al. 2020), in the La Araucanía Region (39º16’ S, 71º48’ W) (Fig. 1). The South American temperate rainforests are one out of only seven of these temperate rainforest ecosystems in the world (Alaback, 1991). These forests cover more than 40,000 km2 along the south-western edge of the continent, mainly in Chile and a small adjacent area in Argentina (CONAF et al., 1999; Donoso, 1993), stretching in latitude south between 35° and 55° (Armesto et al., 1998). They are characterised by cool summers, with precipitation occurring throughout the year. Furthermore, they have been classified as among the world’s 200 biologically most valuable and critically endangered ecoregions (Olson and Dinerstein, 1998) and are considered a Global Biodiversity Hotspot (Myers et al., 2000). In Andean areas, native forest has been reduced by 4..., , # Tree cavity density is a limiting factor for a secondary cavity nester in second-growth Andean temperate rainforests

 

## Altamirano etal 2024 OrnApp BirdData

Unit number: forest stands id

Forest type:

OG: Old-growth Forest

SG: Second-growth Forest

STN ID: Point count number

Season: breeding season

NB Treatment

0: before

1: during

2: after

APHSPI_TOT: Number of individuals of Thorn-tailed Rayaditos

## Altamirano etal 2024 OrnApp VegData

Forest Type: Old- or second-growth forest

Dens DBH > 60: Number of trees greater than 60 cm DBH per hectare

Dens dead trees: Number of standing dead trees per hectare

Peq_dens: cavity density per hectare

Æ© Basal area dens: meters^2 per hectare

DBH (cm): Diameter at breast height

LOG10 (PEQ + 1): Log10 of the Number of small cavities of each tree + 1.