Interconnected nesting success
In our second and third objectives, we predicted that the same cavity
metrics that influenced GFWO nest success would also influence SCB, and
that SCB would have higher nest success in abandoned woodpecker
cavities. As predicted, all SCB had higher nest success rates in
abandoned woodpecker cavities than in natural cavities and cavity type
was the strongest predictor for all species, with the BEWR having the
least impact, followed by the BCTI, and largest influence on ATBC.
Additionally, GFWO had higher success in trees with lower decay and
higher vegetation cover, which was mirrored in SCB; BCTI and ATBC were
more likely to produce fledglings in trees with low decay, and BEWR were
more likely to produce fledglings in cavities with high vegetation
cover. The BEWR was the only species not impacted by decay, potentially
explained by its generalistic nesting behavior
(Taylor,
2003). We observed successful BEWR nests built in metal pipes or
direct sun, thus experiencing wide temperature swings throughout the
day, indicating that unstable nesting environments may be a deterrent
for other cavity nesting birds, but not this species.
Also in line with our third objective, we predicted that abandoned
woodpecker cavities would share characteristics making them better
nesting cavities than natural ones. To this, SCB within our study had
higher success rates within abandoned woodpecker cavities (81-93%),
than in natural cavities (41-56%). The structure of abandoned
woodpecker cavities present on our sites were distinctly different from
their natural counterparts; on average they were significantly higher in
trees, of lower decay, smaller DBH, and increased vegetation cover, all
characteristics that protect eggs and fledglings from shifting internal
temperatures and predation (Copeyon, 1990; Ojeda, Suarez, & Kitzberger,
2007;Pakkala
et al., 2019). Considering that SCB are reliant on pre-existing
cavities to create their nests, the factors that drive the creation and
design of woodpecker cavities may then dictate the success of local SCB.