Phenological Mismatch is Correlated with Fitness Outcomes and
Adaptive Behavior in a Generalist Avian Predator Distributed Across North America
Authors: Callery Kathleen R. 
Published: September 2020

Climate-driven advances in the start of spring may result in a phenological mismatch between
peak-prey abundance and the breeding season of secondary consumers. Phenological mismatch has
been well-studied in insectivorous birds for which reproductive productivity is strongly linked
to caterpillar abundance. The effects of mismatch on the productivity of dietary generalists,
that forage on several types of prey, are less well-understood. Further, few studies have addressed
questions about the effects of mismatch on survival, an important component of fitness that can
be affected by breeding in sub-optimal conditions. We examined the relationship between phenological
mismatch and fitness for a widespread generalist raptor, the American kestrel (Falco sparverius).
In the first chapter, we collected productivity data from nest observations across the contiguous
US and southern Canada and quantified phenological mismatch on each nest as the difference in days
between the start of spring and clutch initiation. Then, we examined the relationship between
mismatch, location, and productivity. Also, we investigated whether incubation behavior leading
to hatching-asynchrony was related to phenological mismatch. Kestrels that laid eggs after the
start of spring had fewer nestlings and higher rates of nest failure compared to kestrels that
laid eggs before the start of spring. The strength of the mismatch effect depended on location.
In the northeast, the number of fledglings per brood and rates of nest success were high for pairs
nesting before the start of spring, but the effect of phenological mismatch was strongest here,
with rapid declines in nest success associated with mismatch. Whereas, in the xi southwest,
early-laying pairs had lower productivity and success relative to the northeast, but the effects
of phenological mismatch were not as strong as the northeast. The effect of location is likely
related to climatic constraints on the growing season and the time window for kestrel breeding
that are becoming stronger in the northeast and weaker in the southwest. The timing of male
incubation behavior was associated with hatching asynchrony, and males breeding after the start
of spring were more likely to initiate incubation early as opposed to males breeding before the
spring index date, suggesting that hatching asynchrony is a possible mechanism to cope with
phenological mismatch.

In the second chapter, we investigated the relationships between phenological mismatch and
survival using mark-and-recapture data from two distinct, long-term study sites in Idaho and
New Jersey where kestrel exhibit difference migration strategies. We created a multistate
mark-recapture models to estimate the annual survival of adult (afterhatch- year) and juvenile
(hatch-year or yearling) kestrels. For the multistate framework, we categorized the phenological
mismatch of nests at each site “earlier” or “later” relative to the yearly median difference in
days between clutch initiation date and the start-of-spring date, which was estimated at each
nest box location. In addition, we included covariates for nesting success, sex, and minimum
winter temperature anomaly in our survival models. Mismatch was associated with the survival of
kestrels that produced young; however, the direction of this effect differed between populations.
In Idaho, successful kestrels had higher survival when they bred “earlier” rather than “later.” In
New Jersey, successful kestrels had higher survival when they bred “later” rather than “earlier."
Differences in survival between sites may reflect differences in seasonality, climate change
patterns, or consequences of migration strategies. For partially migrant xii populations (i.e,
Idaho kestrels), mismatch may rapidly drive directional selection for birds to breed earlier by
favoring survival and productivity, but for fully migrant populations (i.e., New Jersey) that have
a limited window of time to reproduce, mismatch may create trade-offs between reproduction and
survival. Mismatch did not affect the survival of adult birds with failed nests, and there was no
difference in survival between hatch-year birds produced from “earlier” or “later” nests. In Idaho,
males had higher survival rates than females and warmer winter temperatures positively correlated
with survival in all age and sex classes. In New Jersey, sex and winter temperature did not explain
survival. In sum, we found negative consequences of phenological mismatch on the fitness of American
kestrels, generalist predator. For both productivity and survival, the effect of mismatch was more
severe for kestrels in the northeast, where the breeding season is shorter and kestrels more
migratory when compared to the west. These results demonstrate that duration of breeding season
is an important factor to consider when assessing vulnerability to climate change, and that a
generalist diet does not ensure resilience to phenological mismatch.