2015 Southeastern Naturalist Notes Vol. 14, No. 1
N10
J.F. Dwyer, and J.P. Dalla Rosa
Use of Anthropogenic Nest Substrates by Crested Caracaras
James F. Dwyer1,*, and Jeffrey P. Dalla Rosa2
Abstract - Caracara cheriway (Crested Caracara) typically nest in Sabal palmetto (Cabbage Palms)
in Florida and isolated thorny shrubs (e.g., Celtis pallida [Granjeno]) in Texas. The species has not
previously been reported to use anthropogenic nest substrates. We found Crested Caracara nests in
an electrical substation, on a radio tower, and on a billboard near Clewiston, FL, and in an electrical
substation and on a lattice electrical-transmission tower near Houston, TX. Our observations of nesting
on anthropogenic substrates may support 3 distinctly different inferences. First, the behavior could
be ongoing but not previously reported. Second, because individual Crested Caracaras in breeding
plumage persist for years as floaters, novel use of anthropogenic nest substrates may indicate adult
Caracaras seeking any possible nesting opportunity, even if nest success is low. Third, Crested Caracaras
may be modifying their breeding behavior to capitalize on high-quality resources in areas that lack
traditional nest substrates. Comparison of productivity between nests on anthropogenic and natural
substrates would resolve the latter 2 competing hypotheses. Because management focuses primarily
on nest sites, novel nesting-behavior could have important management implications. Future research
should quantify productivity on anthropogenic substrates and document whether individuals produced
at these sites tend to return to anthropogenic substrates to breed.
Introduction. Caracara cheriway Jacquin (Crested Caracara; hereafter Caracara) are
unique among falcons in that Caracaras are the only Falconidae to construct nests (Morrison
and Dwyer 2012). Other falcons nest directly on a substrate, such as a cliff or cave, or
occupy an existing nest built by another species (Ferguson-Lees and Christie 2001). Natural
nest substrates used by Caracaras tend to be consistent within regions but vary among
regions. In Florida, Caracaras nest primarily in Sabal palmetto (Walter) Lodd. ex Schult.
& Schult. f. (Cabbage Palm; Morrison 2007, Smith and Scholer 2013) with scattered individual
records in other trees (Dickinson and Arnold 1996, Morrison and Dwyer 2012). In
Texas, Caracaras nest primarily in Celtis pallida (Klotzsch) Liebm. (Granjeno; Actkinson
et al. 2007) with rare records in other thorny shrubs and trees (Morrison and Dwyer 2012).
In Baja California, Mexico, Caracaras nest primarily in Pachycereus pringlei (S.Watson)
Britton & Rose (Cardon Cactus); records of nests in other cacti are rare (Rivera-Rodríguez
and Rodríguez-Estrella 1998).
Caracaras have not been reported using anthropogenic nest substrates, although it is
possible the behavior occurred historically but was not observed or reported. The closely
related Caracara plancus (Miller) (Southern Caracara) nests on anthropogenic substrates in
Argentina (Seipke 2012; one nest), and Argentinian Patagonia (16 of 35 nests documented
from 2010 through 2013; M. Saggese, Western University of Health Sciences, Pomona, CA,
unpubl. data). Two Phalcoboenus megalopterus Meyen (Mountain Caracara) nests have
been reported on concrete electrical-transmission poles (White and Boyce 1986), and 3 Milvango
chimachima Vieillot (Yellow-headed Caracara) nests were reported in open-topped
boxes affixed to buildings (Johansson et al. 1999). Other than these isolated observations,
caracara species appear to nest consistently in trees (e.g., Daptrius ater Vieillot [Black
Caracara; Whittaker 1996], Milvago chimango Vieillot [Chimango Caracara; Morrison and
Phillips 2000], Southern Caracara [Goldstein 2000], Ibycter americanus (Boddaert) [Red-
1EDM International, Inc., Fort Collins, CO 80525. 2CenterPoint Energy Houston Electric, Houston,
TX 77017. *Corresponding author - jdwyer@edmlink.com.
Manuscript Editor: Karl Miller
Notes of the Southeastern Naturalist, Issue 14/1, 2015
N11
2015 Southeastern Naturalist Notes Vol. 14, No. 1
J.F. Dwyer, and J.P. Dalla Rosa
throated Caracara; McCann et al. 2010]), or on rock ledges or the ground (e.g., Phalcoboenus
australis (Gmelin) [Striated Caracaras]; Raimilla et al. 2014).
Here we report 3 Caracara nests on anthropogenic structures in Florida and 2 Caracara
nests on anthropogenic structures in Texas. We do not know if this behavior is new or simply
not previously reported, but because Caracaras are threatened in Florida, changes in nesting
behavior have important management implications.
Methods. We observed Caracara nests on anthropogenic structures in Florida while
conducting field-work to investigate the ecology of non-breeding and breeding Crested
Caracaras in Florida (Dwyer 2010). This work involved seeking and tracking Caracaras
throughout the species’ range in Florida (Dwyer et al. 2012a, b). We observed nests on
anthropogenic structures in Texas while developing and implementing an avian protection
plan (APP) for CenterPoint Energy Houston Electric. APPs are designed to identify and
mitigate avian electrocution and collision concerns on overhead power systems (APLIC
2006). We determined these structures to be Caracara nests based on our observations of
adult Caracaras attending nests and caring for young.
Results. On 7 February 2007, we found a nest on an A-frame lattice electrical-transmission
tower in a Florida Power and Light (Miami, FL) substation located 6 km south of
Clewiston, FL. The nest was 15 m above the ground, and contained 2 nestlings (Fig. 1). The
substation was surrounded by private property; thus, we were unable to access it again to
determine whether the nest fledged young or was used again in ot her years.
Figure 1. Anthropogenic nest substrates used by Crested Caracaras in Florida, 2007–2009. (A) Location
of nest on A-frame in substation. (B) Close view of 2 nestlings in substation nest. (C) Location
of nest on billboard-support structure; note 1 adult in the nest and another adult on billboard. (D)
Location of nest on radio tower; note adult with prey item in foreground.
2015 Southeastern Naturalist Notes Vol. 14, No. 1
N12
J.F. Dwyer, and J.P. Dalla Rosa
On 4 March 2009, we found a nest on a radio tower 14 km south of Clewiston, FL. The
nest was on a maintenance walkway 20 m above the ground. We observed the nest through
2010 and noted adult Caracaras in the nest in incubating posture suggesting that a clutch
was produced, but we were unable to access the tower to count eggs or nestlings.
On 17 March 2009, we found a nest on a billboard-support structure 6 km west of Lakeport,
FL. The nest was 10 m above the ground and was used annually through 2012 (J.F.
Dwyer, pers. observ; J. Smith, University of Nebraska-Lincoln, Lincoln, NE, pers. comm.).
We observed adult Caracaras annually, but we do not know if this nest produced young.
Each of these nests occurred in landscapes dominated by sugar-cane agriculture.
On 20 March 2014, we found a nest containing 3 eggs on a CenterPoint Energy
Houston Electric (Houston, TX) 138-kV lattice electrical transmission tower, near La
Porte, TX (Fig. 2). The tower supported a power line crossing a 0.75-km-wide ship
channel with the nearest land 0.15–0.25 km southwest, depending on the tide. The nest
was 12 m above the water; it produced 2 eggs and at least 1 fledgling. This structure
had historically supported Ardeidae species (heron and egret nests; Dalla Rosa, unpubl.
data), but those species were absent in 2014.
We found a nest containing 2 eggs on a 138-kV A-frame lattice electrical transmission
tower on 23 March 2014 near Woodgate, TX. The nest was in a 0.5-km2 NRG Energy
(Houston, TX) power-generation facility that served suburban areas. The nest was 21 m
above ground and contained 2 eggs. We identified it during an investigation of a highvoltage
flashover that interrupted electrical service. The location of the nest relative to
Figure 2. Anthropogenic nest substrates used by Crested Caracaras in Texas, 2014. (A) Location of
nest on A-frame in substation. (B) Location of nest on lattice tower. (C) Eggs in nest on lattice tower.
(D) Nestlings in nest on lattice tower.
N13
2015 Southeastern Naturalist Notes Vol. 14, No. 1
J.F. Dwyer, and J.P. Dalla Rosa
high-voltage equipment posed potential electrocution and fire risks to the Caracaras.
Consequently, under a permit issued by the US Fish and Wildlife Service (USFWS), and
with guidance from the USFWS Migratory Bird Office, the nest was removed. Following
the care standards of the National Wildlife Rehabilitators Association (Miller 2000), the 2
eggs were transferred to the Wildlife Center of Texas (Houston, TX), incubated, and the
single resulting chick was raised.
During the time we collected these data in Florida, we studied factors affecting detection
of Caracara nests (Dwyer et al. 2012b); we found and monitored 49 nests on natural
substrates (Dwyer 2010). Thus, 6% of the nests we found in Florida were on anthropogenic
structures. We do not have similar data for Texas because the nests on which we report here
were not found as part of a species-specific nest-monitoring pro gram.
Discussion. Our observations of Caracaras nesting on anthropogenic substrates may
support 3 competing hypotheses. First, Caracaras may have been nesting on anthropogenic
substrates for some time but the nests were not noticed or reported. This suggestion seems
unlikely, particularly in Florida where Caracara nesting has been studied in detail since the
early 1990s (e.g., Dwyer et al. 2012b, Morrison 2007, Morrison and Dwyer 2012, Morrison
and Humphrey 2001, Morrison et al. 1997, Smith and Scholer 2013). Anthropogenic nesting
substrates have not been described previously for this species, though there are reports
of the birds using atypical natural substrates (Morrison et al. 1997). Studies of Caracara
breeding ecology in Texas (Actkinson et al. 2007) and Baja California (Rivera-Rodríguez
and Rodríguez-Estrella 1998) are fewer, but also do not mention nesting on anthropogenic
substrates, even when Caracaras’ relationships to human activities are focal topics (e.g.,
Rodríguez-Estrella 1996). Thus, we believe the nesting behavior reported here is novel.
A second hypothesis is that use of alternate, anthropogenic nest substrates may reflect individuals
accepting any possible nesting opportunity, even if the probability of nest success
is low. Individual adult Caracaras in breeding plumage can persist for years as floaters in
non-breeding groups, presumably seeking but unable to secure a breeding territory (Dwyer
2010; Dwyer et al. 2012a, b). The Caracara population in Florida is thought to be limited by
the availability of nesting territories (reviewed in Dwyer 2010). If this hypothesis is correct,
comparison of nest productivity on natural versus anthropogenic substrates should indicate
lower nest success on anthropogenic structures than on natural substrates.
A third competing hypothesis is that Caracaras are finding high-quality resources in
areas that lack traditional nest substrates, and are modifying their behavior to capitalize
on these resources. Given the species’ ability to use different nest substrates between
regions, and that Caracaras are apparently breeding successfully in natural substrates in
urban areas in Florida (J.F. Dwyer and J.L. Morrison, unpubl. data), this hypothesis seems
most likely. If correct, comparison of nest productivity on natural versus anthropogenic
substrates should indicate greater nest success on anthropogenic structures than on natural
substrates. Thus, nest productivity comparisons may provide simultaneous tests of 2
mutually exclusive competing hypotheses. Simultaneous comparison of productivity in
natural areas to productivity of Caracara nests in urban areas may provide additional insight
into the competing hypotheses.
Caracara nests are typically constructed 4–8 m above ground level (Actkinson et al.
2007, Morrison and Dwyer 2012). The nests reported here were much higher (mean = 15.6
m, SE = 2.2). Young Caracaras typically fledge prior to being well-flighted (Morrison and
Dwyer 2012). Fledglings glide to the ground below the nest and spend 2–3 days sheltering
under low vegetation near the nest substrate before they are able to complete sustained
flights (Morrison and Dwyer 2012). Because we did not monitor nest success, we do not
2015 Southeastern Naturalist Notes Vol. 14, No. 1
N14
J.F. Dwyer, and J.P. Dalla Rosa
know whether higher nests impacted this behavior or whether nesting above open water
might have impacted fledgling survival at the nest in the ship channel. If productivity at various
nest substrates is compared, careful quantification of nest heights would be warranted.
We do not know if Caracaras fledged from anthropogenic substrates tend to return to
anthropogenic substrates to breed, as Falco peregrinus Tunstall (Peregrine Falcon; Tordoff
et al. 1998) and Accipiter cooperii Bonaparte (Cooper’s Hawk; Mannan et al. 2007) do
in a process known as habitat imprinting (Temple 1977) or habitat-preference induction
(Stamps 2001). If imprinting occurs, and if nesting in anthropogenic structures produces at
least as many young per nest as nesting on traditional substrates does, then we would expect
nesting on anthropogenic substrates to become more common in the Florida and Texas
populations. This behavior will have important management implications because current
management strategies for Caracaras in Florida focus almost exclusively on nest sites (reviewed
in Dwyer 2010). Constrictive pressures exerted by habitat loss and fragmentation
in Florida (Morrison and Dwyer 2012) may decrease if Caracaras can breed successfully in
anthropogenic nest substrates or in urban areas. In future research comparing productivity
at anthropogenic versus natural nest substrates, Caracaras produced in anthropogenic or
urban nests should receive unique leg bands to facilitate evaluation of imprinting.
Acknowledgments. CenterPoint Energy Houston Electric, EDM International, Inc.,
and NRG Energy supported this study in Texas. B. Sacra and B. Hughes found and monitored
nests. S. Schmalz and M. Pickell cared for nestling Caracaras until they could be
released. J. Fraser and J. Morrison advised the Ph.D. Dissertation research at Virginia Tech
that informed and facilitated documentation of anthropogenic nest substrates in Florida.
D. Eccleston, R. Harness, K. Miller, J. Smith, and 3 anonymous reviewers provided helpful
comments on drafts of this manuscript.
Literature Cited
Actkinson, M.L., W.P. Kuvlesky, Jr., C.W. Boal, L.A. Brennan, and F. Hernandez. 2007. Nestinghabitat
relationships of sympatric Crested Caracaras, Red-tailed Hawks, and White-tailed Hawks
in South Texas. Wilson Journal of Ornithology 119:570–578.
Avian Power-Line Interaction Committee (APLIC). 2006. Suggested practices for avian protection
on power lines: The state of the art it 2006. Edison Electric Institute, APLIC, and the California
Energy Commission, Washington DC, and Sacramento, CA.
Dickinson, V.M., and K.A. Arnold. 1996. Breeding biology of the Crested Caracara in south Texas.
Wilson Bulletin 108:516–523.
Dwyer, J.F. 2010. Ecology of non-breeding and breeding Crested Caracaras (Caracara cheriway) in
Florida. Ph.D. Dissertation. Virginia Polytechnic Institute and State University, Blacksburg, VA.
Dwyer, J.F., J.D. Fraser, and J.L. Morrison. 2012a. Within-year survival of non-breeding Crested
Caracaras. Condor 114:295–301.
Dwyer, J.F., J.L. Morrison, and J.D. Fraser. 2012b. Factors influencing detection of nesting Crested
Caracaras. Journal of Wildlife Management 75:857–862.
Ferguson-Lees, J., and D.A. Christie. 2001. Raptors of the World. Houghton Mifflin Company, Boston,
MA. 992 pp.
Goldstein, M.I. 2000. Nest-site characteristics of Crested Caracaras in La Pampa, Argentina. Journal
of Raptor Research 34:330–333.
Johansson, C.A., E.T. Linder, C.M. White, and J.C. Lyra Fleury. 1999. Nesting observations of the
Yellow-headed Caracara in the Cerrado region of Brazil. Ornithologia Neotropical 10:211–215.
Mannan, R.W., R.N. Mannan, C.A. Schmidt, W.A. Estes-Zumpf, and C.W. Boal. 2007. Influence
of natal experience on nest-site selection by urban-nesting Cooper’s Hawks. Journal of Wildlife
Management 71:64–68.
McCann, S., O. Moeri, T. Jones, S. O’Donnell, and G. Gries. 2010. Nesting and nest-provisioning
of the Red-throated Caracara (Ibycter americanus) in central French Guiana. Journal of Raptor
Research 44:236–240.
N15
2015 Southeastern Naturalist Notes Vol. 14, No. 1
J.F. Dwyer, and J.P. Dalla Rosa
Miller, E.A. 2000. Minimum Standards for Wildlife Rehabilitation, 3rd Edition. National Wildlife
Rehabilitators Association, St. Cloud, MN. 76 pp.
Morrison, J.L. 2007. Characteristics of nest sites used by Crested Caracaras in south-central Florida.
Florida Field Naturalist 35:1–8.
Morrison, J.L., and J.F. Dwyer. 2012. Crested Caracara (Caracara cheriway). Number 249, In A.
Poole (Ed.). The Birds of North America online. Cornell Lab of Ornithology, Ithaca, NY. Available
online at http://bna.birds.cornell.edu/bna/species/249. Accessed 1 September 2014.
Morrison, J.L., and S.R. Humphrey. 2001. Conservation value of private lands for Crested Caracaras
in Florida. Conservation Biology 15:675–684.
Morrison, J.L., and L.M. Phillips. 2000. Nesting habitat and success of the Chimango Caracara in
southern Chile. Wilson Bulletin 112:225–232.
Morrison, J.L., M.A. McMillian, S.M. McGehee, and D. Todd. 1997. First record of Crested Caracaras
nesting in a cypress. Florida Field Naturalist 25:51–53.
Raimilla, V., C.G. Suazo, G. Robertson, and J.R. Rau. 2014. Observations suggesting cooperative
breeding by Striated Caracaras (Phalcoboenus australis). Journal of Raptor Research 48:189–191.
Rivera-Rodríguez, L.B., and R. Rodríguez-Estrella. 1998. Breeding biology of the Crested Caracara
in the cape region of Baja California, Mexico. Journal of Field Ornithology 69:160–168.
Rodríguez-Estrella, R. 1996. Response of Common Black Hawks and Crested Caracaras to human
activities in Mexico. Pp. 356–363, In D.M. Bird, D. Varland, and J.J. Negro (Eds.). Raptors in
Human Landscapes. Academic Press, London, UK. 396 pp.
Seipke, S.H. 2012. First record of Southern Caracaras (Caracara plancus) nesting on a human-made
object. Journal of Raptor Research 46:228–230.
Smith, J.A., and M.N. Scholer. 2013. Nest components of Crested Caracaras (Caracara cheriway)
breeding in Florida. Florida Field Naturalist 41:42–48.
Stamps, J.A. 2001. Habitat selection by dispersers: Integrating proximate and ultimate approaches.
Pp. 230–242, In J. Colbert, E. Danchin, A.A. Dhondt, and J.D. Nichols (Eds.). Dispersal. Oxford
University Press, New York, NY. 480 pp.
Temple, S.A. 1977. Manipulating behavioral patterns of endangered birds: A potential management
technique. Pp. 435–443, In S.A. Temple (Ed.). Endangered birds. The University of Wisconsin
Press, Madison, WI. 468 pp.
Tordoff, H.B., M.S. Martell, and P.T. Redig. 1998. Effects of fledge site on choice of nest site by
Midwestern Peregrine Falcons. Loon 70:127–129.
White, C.M., and D.A. Boyce. 1986. Notes on Mountain Caracara (Phalcoboenus megalopterus) in
the Argentine puna. Wilson Bulletin 99:283–284.
Whittaker, A. 1996. Nesting records of the genus Daptrius (Falconidae) from the Brazilian Amazon,
with the first documented nest of the Black Caracara. Ararajuba 4:107–109.