Saborse and Renne • HISTORIC PRESENCE AND ABSENCE OF PREDATORS 
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Ohio Breeding Bird Atlas II data, as well as 
information from local park managers and 
experienced ornithologists (e.g.. no screech-owls 
have been reported in the latter sites in the last 
10-30 years; R. J. Novotny and R. C. Jones, and 
other local park managers, pers. comm.). 
Sample Size.—We acknowledge our small 
sample si/e could be problematic but believe 
our findings are valid for three main reasons. 
First, regional dialectical differences seem un¬ 
likely since chickadees in screech-owl areas were 
sampled from populations separated by 39 km 
and the only variable distinguishing these sites 
from all others was screech-owl presence (Fig. 1). 
Second, unlike song structures, which can vary 
greatly over short temporal and spatial scales in 
many songbirds (Slater 1986, Gammon et al. 
2005), warning call structures exhibit remarkable 
consistency across large areas and habitat types 
(Ippi et al. 2011). The 'chick-a-dee' warning call 
of Black-capped Chickadees seems highly con¬ 
served throughout its North American range 
(Hurd 1996 [Wisconsin], Baker and Becker 2002 
[Colorado], Templeton et al. 2005 [Montana], 
Avey et al. 2011 |Alberta, Canada], this study 
[Ohio]), Third, small sample size can lead to false 
positives and the likelihood of this would increase 
if by chance young birds happened to be caught 
that had not yet learned the calls from adults. 
However, the 12 Chickadees were tested from 
February to early May and nestlings Hedge in 
May; thus, few if any young could have been 
caught. 
RESULTS 
Call and Statistical Analysis.—We recorded 
231 ‘chick-a-dee’ calls from 12 individuals. 
Black-capped Chickadees from non-screech-owl 
areas produced 93 calls (n = 8 individuals, mean 
± SE = 11.6 ± 6.1) while chickadees from 
screech-owl areas produced 138 calls (n = 4 
individuals, mean ± SE = 34.5 ± 8.6). This 
197% increase in average call number per 
individual was only marginally significant when 
using log-transformed data with homogenous 
variances (Fig. 2A; Ft. io - 3,65. P = 0.085). 
Individuals from areas without and with screech- 
owls, respectively, averaged 2.30 and 4.40 D 
notes per call (median = 2.22). which represented 
a 91% higher number of D notes per call in areas 
with Eastern Screech-Owls (Fig. 2B, Fig. 3 ; F U o 
= 7.64, P = 0.020). The duration of the first D 
note produced by chickadees in areas without 
screech-owls was 36% longer than in areas with 
them (Fig. 2C. Fig. 3; F,., 0 = 6.44. P = 0.030) 
and the time between the first and second D notes 
was 44% longer (Fig. 2D. Fig. 3; Fuo = 4.58, 
P - 0.058). There was no significant difference in 
length of lime between the ‘chick-a’ and the D 
notes between the two groups (Fuo = 2.03. P = 
0.19). 
DISCUSSION 
Faunal community structure is spatially and 
temporally dynamic as predator composition 
changes over space as well as generations of prey 
(Griffin 2004). This raises a fundamental question 
as to whether absence of a historically sympat- 
ric predator results in loss of recognition or an 
acoustical change in learned calls for that 
predator. Evidence suggests it is not the former 
and that deterioration in predator recognition can 
be recalcitrant (Curio 1993, Blumstein 2006). 
Maintenance of adaptive response to unfamiliar 
predators is particularly likely for continental 
species, as their lineages have been subjected to 
different predator archetypes (Blackburn et al. 
2004, Cox and Lima 2006); presence of a 
functionally similar predator is also sufficient 
for persistence of threat recognition for a currently 
absent but historically sympalric predator (Blum¬ 
stein 2006). 
Black-capped Chickadees have many similar- 
sized avian predators such as Cooper’s Hawks 
(Accipiter cooper'd). Sharp-shinned Hawks (A. 
striatus), and American Kestrels (balco sparver- 
i„s), and it is unlikely the low-threat -chick-a-dee' 
calls produced in areas without screech-owls 
(Figs. 2. 3) reflect loss of predator recognition 
but rather resulted from failure to learn vocaliza¬ 
tions for them. Learning call structures in many 
songbirds is requisite for producing and respond¬ 
ing to them (Hughes et al. 1998, Gill and Sealy 
2004. Avey et al. 2011). and predator absence can 
alter learned anti-predator vocalizations in one 
generation (Blumstein et al, 2004). We did not test 
different-size predator models or measure re¬ 
sponses to playbacks of our recorded calls and it 
remains possible that chickadees in areas without 
screech-owls coincidentally elicit calls with few 
D notes which convey high threat. This is unlikely 
because 'chick-a-dee' calls designating high 
threat and the responses to them, albeit learned, 
seem highly conserved throughout North America 
(Hurd 1996. Baker and Becker 2002, Templeton 
et al. 2005. Templeton and Greene 2007, Avey 
