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2014 SOUTHEASTERN NATURALIST 13(1):156–165
Interactions Between Wildlife and Civil Aircraft in
Mississippi
Kelsey M. Drey1, James A. Martin1,*, Jerrold L. Belant2, Travis L. DeVault3,
and Bradley F. Blackwell3
Abstract - Collisions between aircraft and wildlife have increased markedly since first recorded
in 1905. These strikes threaten human safety and cost the United States civil aviation
industry >$677 million annually. We examined the Federal Aviation Administration’s national
wildlife strike database records from 1990–2010 to characterize reported strikes with civil
aircraft in Mississippi. We hypothesized that daily foraging patterns and seasonal differences
would affect strike frequency for birds. We summarized 381 reported strikes (366 birds, 14
mammals, and 1 reptile) comprising ≥42 species. Bird strikes per 1000 aircraft operations
(take-off and landing counted as separate operations) increased between 1990–2010. The
monthly number of reported strikes per 1000 operations peaked July–September, coinciding
with late breeding season and fall migration. Bird strikes per 1000 operations occurred more
often during runway approach than during take-off, and more often at dusk than during other
times of day. These patterns mirrored nationally observed wildlife-strike patterns. Our results
may aid airport biologists in Mississippi to prioritize species management and more effectively
implement timing and types of animal control efforts.
Introduction
Wildlife–aircraft collisions (hereafter, strikes) pose increasing safety and financial
threats to civil aviation. These strikes result in an estimated annual worldwide
cost exceeding $1.2 billion (Allan 2002, Blackwell et al. 2009a, Dolbeer and Wright
2008). Globally, strikes involving birds have caused 276 human deaths and destroyed
108 civil aircraft (Thorpe 2010). In the US, estimates suggest that strikes cost the civil
aviation industry >$677 million dollars in 2010 (Dolbeer et al. 2012) and caused 24
human fatalities and 235 injuries from 1990–2010 (Dolbeer et al. 2012). The Federal
Aviation Administration (FAA) anticipates a 3.5% annual increase in US civil aircraft
traffic through 2025 and construction of additional runways (FAA 2008), suggesting
a continued increase risk of wildlife strikes (Blackwell et al. 2009a).
Wildlife abundance and habitats beyond airport boundaries are an important
consideration when managing strike risk (Dolbeer 2011, Martin et al. 2011), particularly
within approach and departure zones of aircraft runways (Blackwell et al.
2009a, Dolbeer 2006). Despite management success in reducing wildlife strikes
within boundaries (i.e., generally at altitudes less than 152 m [500 ft]; Dolbeer 2011),
regional priorities for wildlife management at airports differ. For example, with
1Department of Wildlife, Fisheries, and Aquaculture, Mississippi State University, Mississippi
State, MS, 39762. 2Center for Resolving Human–Wildlife Conflicts, Mississippi
State University, Mississippi State, MS, 39762. 3USDA, APHIS, Wildlife Services, National
Wildlife Research Center, Ohio Field Station, 6100 Columbus Avenue, Sandusky, OH
44870. *Corresponding author - jmartin@cfr.msstate.edu.
Manuscript Editor: Frank R. Moore
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increasing urbanization in the US, a variety of bird species, and mammals such as
Odocoileus virginianus Zimmermann (White-tailed Deer) and Canis latrans Say
(Coyote), have adapted to urban environments and use airport habitats (Dolbeer
and Wright 2009). Blackwell et al. (2013) suggested that by integrating our understanding
of species’ seasonal use of resources for foraging and breeding with a
knowledge of antipredator behaviors, managers can manipulate both resources and
perceived risk to reduce wildlife use of airport habitats.
In Mississippi, airports are exposed to birds migrating along the Mississippi
and Atlantic Flyways (Bellrose and Sieh 1960). Wildlife managers in the state are
increasingly confronted with management of large bird and mammal populations
that exploit agriculture and aquaculture resources, and pose a potential strike risk
through their use of airport habitats. We sought to gain a better understanding of
the species struck by aircraft at Mississippi airports relative to year-to-year dynamics,
within-year dynamics, time of day, and phase of flight. We hypothesized that
seasonal biological influences, such as bird migration, would affect the frequency
of strikes due to the influx of individuals moving through Mississippi, much as
collisions with wind turbines have seasonal influences in other geographic areas
(Hüppop et al. 2006). We expected that the fall migration period would have the
greatest strike rate because bird abundance increases after the breeding season
(Dolbeer et al. 2012). We also hypothesized that daily foraging patterns would be an
important factor in bird-aircraft interactions, and we predicted a greater frequency
of strikes at dawn and dusk. We also predicted that most strikes would occur during
the approach phase of flight because the aircraft is moving at a slower speed than
at take-off (Dolbeer et al. 2012). Our objectives were to evaluate temporal and spatial
patterns in wildlife strikes reported to the FAA for airports in Mississippi and
develop management guidance relative to these findings.
Methods
We tested our hypotheses using records from the FAA national wildlife strike database
for the state of Mississippi. The FAA national wildlife strike database consists
of information that is voluntarily reported to the FAA by pilots and airports using
FAA Form 5200-7 (Dolbeer et al. 2012). Data in these reports include the airport,
wildlife species involved, size of the animal, time of day, severity of aircraft damage,
month, year, and phase of flight. We queried the database for the years 1990–2010 using
the keywords Mississippi and civil aircraft to obtain data for this study. Because
not all reports were complete, sample sizes varied among comparisons.
We summarized the reported strikes using the FAA’s air traffic activity system
airport operation data from 1990–2010 for civil aircraft in Mississippi (FAA 2012).
We identified the number of species or species groups involved in reported strikes
from these reports. We also classified these groups in relation to hazard-level rank
(DeVault et al. 2011, Dolbeer and Wright 2009). Because birds represented 96% of
reported strikes, we evaluated only bird strikes in our analyses, but include descriptive
statistics for other taxa (Table 1). We considered each take-off and landing as
a separate operation and standardized the number of reported bird strikes per 1000
operations based on data from the air traffic activity system report (FAA 2012).
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We then calculated the frequency of standardized strikes by phase of flight—taxi,
take-off run, climb, approach, and landing. Take-off run and landing are when the
aircraft altitude is at 0 m above ground level (AGL), climb is from 0 m AGL to
cruising altitude, and approach will vary depending upon required rate of descent
from altitude (US DOT FAA 2007).
Table 1. Number of reported wildlife strikes (n = 381) with US civil aircraft and associated hazard
level by bird species, Mississippi, 1990–2010. Hazard level values were assigned by Dolbeer and
Wright (2009).
Group Strikes reported Hazard level
Unknown small bird 111
Unknown medium bird 62
Zenaida macroura (L.) (Mourning Dove) 43 Moderate
Charadrius vociferous (L.) (Killdeer) 16 Low
Gulls 13 Very high
Swallows 13 Very low
Blackbirds 12 Low
Hawks 12 Moderate
Meadowlarks 10 Low
Sparrow 10 Low
Unknown large bird 10
Geese 7 Extremely high
Odocoileus virginianus (Z.) (White-tailed Deer) 7 Extremely high
Vultures 6 Extremely high
Ducks 5 Extremely high
Canis latrans (S.) (Coyote) 5 High
Unknown bird 4
Owls 3 High
Sturnus vulgaris (L.) (European Starling) 3 Moderate
Turdus migratorius (L.) (American Robin) 3
Columba livia (G.) (Rock Pigeon) 2 High
Mimus polyglottos (L.) (Northern Mockingbird) 2 Low
Progne subis (L.) (Purple Martin) 2 Low
Ardea Herodias (L.) (Great Blue Heron) 2 Very high
Haliaeetus leucocephalus (L.) (Bald Eagle) 1 Extremely high
Corvus brachyrhynochos (B.) (American Crow) 1 High
Egret 1 High
Canis lupus familiaris (L.) (Domestic Dog) 1 Very high
Melegris gallopavo (L.) (Wild Turkey) 1 Very high
Falco sparverius (L.) (American Kestrel) 1 Very low
Chaetura pelagica (L.) (Chimney Swift) 1 Very low
Chordeiles minor (F.) (Common Nighthawk) 1 Very low
Scolopax minor (G.) (American Woodcock) 1
Molothrus ater (B.) (Brown-headed Cowbird) 1
Bos primigenius (B.) (Cattle) 1
Sialia sialis (L.) (Eastern Bluebird) 1
Eremophila alpestris (L.) (Horned Lark) 1
Grus Canadensis (L.) (Sandhill Crane) 1
Porzana carolina (L.) (Sora) 1
Tern 1
Turtle 1
Gallinago delicata (O.) (Wilson's Snipe) 1
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We calculated the total number of reported strikes and the number of strikes by
period of day, with dawn and dusk representing 0.75 hr and night and day 11.25 hr
per diel period (after Biondi et al. 2011, Wright et al. 1998). Therefore, strikes were
standardized by hours per diel period, but we could not standardize these values
by number of operations because insufficient data were available in publicly accessible
databases.
We used linear regression to compare the number of reported strikes (standardized
by number of operations) by year and used piecewise regression to detect
seasonal thresholds in strike rates. We compared models using Akaike’s information
criterion (AIC) (Burnham and Anderson 2002). We used goodness-of-fit tests
to compare numbers of reported strikes by aircraft movement type and season with
95% confidence intervals. We also used goodness-of-fit tests to compare time of
day, and then we applied the Marascuilo procedure to find significance between
differences in proportions (Berenson et al. 2012). We used program R (R Development
Core Team, 2011) with a priori statistical significance determined by α ≤ 0.05
for all analyses.
Results
There were 381 reported strikes with US civil aircraft in Mississippi from 1990–
2010 (Table 1). Birds accounted for 96% of reported strikes (n = 366; Table 1) at 20
airports, with 81% at Jackson-Medgar Wiley Evers International Airport and Gulfport
Biloxi Regional Airport (Fig. 1). Wildlife categorized at the moderate or greater
hazard level (Dolbeer and Wright 2009) accounted for 62% of total reported strikes.
Figure 1.
N u m b e r
of reported
bird
s t r i k e s
(n = 333)
with US
civil aircraft
in
Mississippi,
1990–
2010.
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The number of reported bird strikes per 1000 operations increased from 1990 to
2010, (r2 = 0.77, P < 0.01, df = 18; Fig. 2). Within years, the number of reported
bird strikes per 1000 operations has a distinct seasonal pattern showing no change
in strikes from January to April (-0.006, ± 0.014), an increase from April to July
(0.051, ± 0.017), and a decline from July to December (-0.066, ± 0.011) (r2 = 0.87,
P < 0.03, df = 6; Fig. 3). Reported strikes were more frequent during approach than
during other operations (χ4
2 = 120.53, P < 0.01; Fig. 4). The greatest number of
reported strikes-per-hour occurred during dusk, followed by dawn, day, and night,
respectively (χ3
2 = 17.87, P < 0.01; Fig. 5); strike rate differed significantly between
dusk and night.
Discussion
A recent 25% increase in strike reports across the US presumably has been in
response to the 2009 Hudson River bird-strike incident in which an airliner carrying
155 people was ditched after hitting at least one bird (Dolbeer et al. 2012,
Marra et al. 2009). Similarly, we found an increase in reported strikes since 2009
in Mississippi (Fig. 2). However, Dolbeer (2011) found that strike rates outside
the airport environment (>152 m above ground level) increased in the years preceding
2009; thus, increased reporting does not entirely explain the increase in
reported strikes. For 51% of the reported strikes in the FAA database, the birds
involved were not identified to species (Dolbeer et al. 2012). The FAA encourages
airport personnel to collect and send bird parts recovered from strikes to the
Figure 2. Number of reported bird strikes with US civil aircraft (n = 366) reported per year
in Mississippi, 1990–2010.
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2014 Vol. 13, No. 1
Figure 3. Rate
of bird strikes
(n = 366) with
US civil aircraft
by month
(±95% CI) in
Mis s i s s i p p i ,
1 9 9 0 – 2 0 1 0 .
The piecewise
regression is
defined as y =
0.06 + -0.004 *
x * I(x < c1) +
0.051 * x * I(c2
> x > c1) -0.066
* x * I(x > c2),
where x is the
month, ci is the
breakpoint, and
I is an indicator.
Estimated
breakpoints, c1
and c2, were 4.0
± 0.68 (SE) and
7.3 ± 0.40 (SE),
respectively.
Figure 4. Percent (+95% CI) of reported bird strikes (n = 286) with US civil aircraft by type
of aircraft movement in Mississippi, 1990–2010.
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Smithsonian Institute in Washington, DC for identification to species (Dolbeer et
al. 2012).
Mississippi airports with the most reported strikes were among the largest and
busiest: Jackson Evers International (Jackson, MS), Gulfport Biloxi Regional (Biloxi,
MS), and Golden Triangle Regional (Columbus, MS). All of these airports
are located near urban environments and major water bodies. These environments
harbor many of the species struck in Mississippi, including Branta canadensis
(Canada Goose), Charadrius vociferous (Killdeer) and gulls. Mississippi is a mostly
rural state with few population centers, and most strikes occur at airports near
those centers. Future urban development around existing airports should consider
the risk to aviation as a consequence of development (Blackwell et al. 2009a).
We predicted more bird strikes during spring and fall during bird migration. We
found the number of strikes was steady from January to April, increased markedly
Figure 5. Number and rate (+95% CI) of bird strikes (n = 307) with US civil aircraft by
time of day in Mississippi, 1990–2010, with statistical significance between dusk and night.
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2014 Vol. 13, No. 1
from April to July, then followed by a decline from July to December. The increase
in April through July may be associated with increased movements to establish
breeding territories and undertake courtship (Greenwood and Harvey 1982), as
well as the influx of inexperienced juveniles that may be more likely to collide with
aircraft (Arnett et al. 2008).
Analysis of the FAA data supported our predictions regarding diel patterns of
bird strikes. We based our initial predictions on bird biology—foraging mostly occurs
in morning and evening making an interaction with aircraft more likely during
those times (Bednekoff and Houston 1994, Coleman and Richmond 2007). Our
results show that most strikes occurred during dusk. This finding highlights the possibility
that food acquisition and movements to roost sites are the primary reasons
that birds use the airport environment, as has been suggested by others (Blackwell
et al. 2013, DeVault and Washburn 2013). Birds may also be impaired by reduced
visibility in low-light conditions, reducing the birds’ ability to make effective behavioral
responses to aircraft. Birds are known to respond to aircraft by attempting
to avoid being struck (Bernhardt et al. 2010), but we know of no studies that explain
how environmental conditions affect response times.
Our results support our prediction that most strikes occurred during the approach
phase. Dolbeer (2006) showed that 74% of all strikes occur at less than 152 m (less than 500 ft)
AGL. We hypothesize that birds’ response to aircraft varies with aircraft flightphase
because of differences in flight speeds, angle of the aircraft, and noise levels
(Bernhardt et al. 2010, Blackwell et al. 2009b). We believe that current work on
birds’ response to aircraft lighting and color-scheme design will help to improve
understanding of bird avoidance-behavior (e.g., Blackwell et al. 2012).
Because the FAA anticipates a 3.5% increase in US civil aircraft traffic
through 2025 (FAA 2008), we encourage additional management efforts to reduce
bird strikes (see Dolbeer et al. 2012), with emphasis on time periods of greatest
bird movement and use of the airport environment such as migration and twilight
hours. Research and monitoring of the airport environment will elucidate the
mechanisms driving patterns of bird movement and will inform risk-mitigation
strategies. We recommend that managers identify struck birds to species to finetune
management approaches. Fortunately, none of these strikes has caused major
property loss or major human injury in Mississippi; however, wildlife–aircraft
strikes are inevitable and through proper reporting, bird monitoring, continued research
in deterring birds, and implementation of management recommendations,
we can decrease strike risk.
Acknowledgments
This study was supported by Mississippi State University, the FAA, and the US Department
of Agriculture’s National Wildlife Research Center. We would like to thank S.E.
Wright and K.M. Biondi for assisting with the FAA database. This manuscript was improved
by the comments of one anonymous reviewer and D.J. Twedt. Opinions expressed in this
manuscript do not necessarily reflect current FAA policy decisions regarding the control of
wildlife on or near airports.
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