Secondhand homes: Woodpecker cavity location and structure influences
secondary nester’s success.
Abstract
1. Understanding how ecosystem engineers influence other organisms has
long been a goal of ecologists. Woodpeckers select nesting sites with
high food availability and will excavate and then abandon multiple
cavities throughout their lifetime. These cavities are crucial to
secondary cavity nesting birds (SCB) that are otherwise limited by the
availability of naturally occurring cavities. 2. Our study examined the
influence of food resources on the nest site location and home-range
size of woodpeckers, and the subsequent influence of woodpeckers on the
nesting success of SCB. 3. Using five years of avian point count data to
locate golden-fronted woodpeckers (GFWO), we correlated insect
availability with GFWO home range size, determined differences in insect
availability between GFWO occupied and unoccupied sites, and compared
nesting success for the GFWO and common SCB in south Texas. We used
model averaging to fit species-specific logistic regression models to
predict nest success based on cavity metrics across all species. 4.
Sites occupied by GFWO had a higher biomass of insects in orders
Coleoptera, Hymenoptera, and Orthoptera than unoccupied sites, and there
was a negative correlation between the availability of these insect
orders and home-range size. GFWO nest success increased with vegetation
cover and lower levels of tree decay. SCB had higher levels of nesting
success in abandoned GFWO, and in trees with lower levels of nest tree
decay. 5. Our results suggest that SCB may be drawn to nest in abandoned
woodpecker cavities where they have higher rates of nest success
compared to natural cavities. Additionally, the prevalence for GFWO to
excavate cavities in trees with lower levels of decay contradicts
previous literature, and may indicate a novel temperature trade-off,
with live trees requiring more energy to excavate, but providing
increased protection from high breeding season temperatures in arid and
semi-arid areas.