Flight Speeds of Northern Pintails during Migration Determined Using Satellite Telemetry

2005·7.4 MB·English

by  Michael R Miller

Wilson Bulletin 117(4):364-374, 2005
FLIGHT SPEEDS OF NORTHERN PINTAILS DURING MIGRATION
DETERMINED USING SATELLITE TELEMETRY
MICHAEL R. MILLER,'•= JOHN Y. TAKEKAWA,^ JOSEPH P. FLESKES,'
DENNIS L. ORTHMEYER,’-'* MICHAEL L. CASAZZA,' DAVID A. HAUKOS,^
AND WILLIAM M. PERRY'
ABSTRACT. Speed (km/hr) during flight is one of several factors determining the rate of migration (km/
day) andflightrangeofbirds. Weattached26-g,back-mountedsatellite-receivedradiotags(platformtransmitting
terminals; PTTs) to adult female Northern Pintails {Anasacuta) during (1) midwinter2000-2003 in the northern
Central Valley ofCalifornia, (2) fall and winter 2002-2003 in the PlayaLakes Region and GulfCoastofTexas,
ainnsdta(n3c)ese,arolbytafailnle2d0m0u2l-t2ip0l0e3lioncastoiuotnhs-cdeunrtirnagl NsiengwleMemxiigrcaot.orWyefltirgahctkse(dfltiagghtgepdatbhisr)d.sWaefteursreedledaasteaafnrd,omin17sevPeTrTa-l
tagged hens along 21 migratory flight paths to estimate groundspeeds during spring {n = 19 flights) and fall (n
= 2 flights). Pintails migrated at an average groundspeed of77 ±4 (SE) km/hr(range forindividual flightpaths
= 40-122 km/hr), which was within the range of estimates reported in the literature for migratory and local
fk1lm7i/ghhotfrstiohnfetw2aai1tlwefirlnfidgoshw.tlpAa(tt4h2as-t1oy1cp6iccuakrlmr,/ehdbru)ti;nhftyuapriotlthwheiernt,discgarlwo,iutnfhldisagphnteeaadvlteairtvauegdreeagoaeifdrs1p5,e43e6d0±omf65(k58m5/0±hrm4iilnlkimhb/aehrras,dwsaitnnadndds4aradoncdpcrue8rs2rseudr±e)m4,
headwindswithan average airspeedof71 ±4kmyOir. These adjustmentsinairspeedandgroundspeedinresponse
to wind suggest that pintails migrated at airspeeds that on average maximized range and conserved energy, and
fell within the range ofexpectations based on aerodynamic and energetic theory. Received 19November2004,
accepted 6 September2005.
The overall rate at which birds travel during of migration (the number ofbirds aloft; Rich-
migration, often referred to as migration speed ardson 1990). For many birds, migration
(measured in km/day), includes the time re- speed may be controlled largely by the time
quired to accumulate fat reserves and rest pri- required to acquire fat reserves at stopovers
or to migration and at stopovers, and the ac- (Alerstam 2003). However, Liechti and Bru-
tual time spent in flight during which fat is derer (1998) concluded that for birds making
catabolized (Alerstam and Lindstrom 1990). long nonstop flights, selection of favorable
Flight speed (km/hr) is expressed as ground- tailwinds to boost groundspeed and save en-
speed (velocity with respect to ground) or air- ergy (fat) is more important than timing de-
speed (velocity with respect to air); the ratio parture based on the rate of fat accumulation.
of groundspeed to airspeed directly measures Birds in headwinds, for example, may lower
the effects of wind on the energetic costs of flight altitude until wind velocity declines,
migration (Alerstam 1978, Richardson 1990). thereby increasing groundspeed and conserv-
This ratio is proportional to migration speed ing energy (Kerlinger and Moore 1989).
(Alerstam 2003), and can predict the strength Birds migrate at groundspeeds that reflect,
among other things, airspeed in the presence
or absence of tailwinds or headwinds (Rich-
* U.S. Geological Survey, Western Ecological Re- ardson 1990, Alerstam 2003) and aerodynam-
search Center, Dixon Field Station, 6924TremontRd., ic characteristics of the species (Pennycuick
Dixon, CA 95620, USA. 1975, Rayner 1990). Aeronautical flight me-
2U.S. Geological Survey, Western Ecological Re- chanics and bioenergetics theory suggest that
tsieoanr,ch50C5enAtzeru,arSaDrn.,FVraalnlceijsoc,oCBAay94E5s9t2u,arUySAFi.eld Sta- birds should fly at one of two characteristic
3U.S. Fish and Wildlife Service, Dept, of Range, airspeeds during migration. The first minimiz-
Wildlife, and Fisheries Management, Texas Tech es energy cost per unit of time to remain air-
Univ., Lubbock, TX 79409, USA. borne as long as possible (minimum powei
^Currentaddress: CaliforniaWaterfowlAssociatiConA, speed; V^^), and the second minimizes the en-
4630 Northgate Blvd., Ste. 150, Sacramento, ergy cost per unit of distance flown to maxi-
95834, USA. mize distance over the ground with a certair
^Corresponding author; e-mail:
[email protected] fuel load (maximum range speed; Vny.) (Tuckei
364
Milleret al. • PINTAIL FLIGHT SPEED 365
and Schmidt-Koenig 1971, Alerstam and Hed- 51' W). These areas are located in important
A
enstrom 1998). third conceptual speed, pintail wintering or fall staging regions (Bell-
which is not as well defined (Bruderer and rose 1980).
Boldt 2001), minimizes total duration of the We tagged only adult female pintails be-
migration by maximizing overall speed (min- cause of their critical role in population dy-
imum time speed; however, in practice it namics (Flint et al. 1998). We sorted all hens
is rarely separable from (Alerstam and by sex and age (Carney 1992), attached fed-
Hedenstrom 1998, Hedenstrom and Alerstam eral leg bands, and obtained body mass (±5
1998). In general, waterfowl are well designed g). We used Model 100 PTTs fromMicrowave
for relatively rapid long-distance migration Telemetry, Inc. (Columbia, Maryland), and
(Rayner 1988), and the moderately sized annually attached 25-55 on females in Cali-
Northern Pintail {Anas acuta), in particular, fornia, 20 in Texas, and 6-9 in New Mexico.
features an aerodynamic design (streamlined The units, with harness and protective neo-
shape, long narrow wings) that supports effi- prene pad, weighed about 26 g, which was
cient long-distance flight (Pennycuick 1975, 2.7-3.2% of average body mass at capture in
Bellrose 1980, Bruderer and Boldt 2001). California (900-950 g), Texas (820-920 g),
However, it is not known whether pintails mi- and New Mexico (935-975 g), well under
grate with flight speeds that adhere to theo- commonly used guidelines (Caccamise and
retical models. Hedin 1985). We attached each PTT dorsally
Investigators have used satellite telemetry between the wings by fashioning a harness of
to estimate the groundspeeds of migrating 0.38-cm-wide (sold as 3/16 in) Teflon ribbon
swans (Cygnus spp.; Pennycuick et al. (Bally Ribbon, Bally, Pennsylvania). The
1996a, Ely et al. 1997) and Brant {Branta completed harness included fore and aft body
bernicla; Green et al. 2002), but we found loops connected with a 1-cm-length ofribbon
no such information for ducks. A recent pro- over the keel, similar to designs used by Ma-
ject to track migration of adult female pin- lecki et al. (2001). Ours, however, consisted
tails outfitted with satellite-receiving radio of a single length of ribbon without metal
tags (platform transmitting terminals; PTTs) clips, buckles, shrink-tubing, or sewed areas,
in California, Texas, and New Mexico win- and we hardened knots with cyanoacrylate
tering regions (Miller et al. 2001, 2005) pro- glue. We released ta—gged hens at trap sites 5-
vided an opportunity to directly estimate 19 hr after capture either during evening
groundspeed. By using archived speeds and pintail flights or at night.
directions of winds at a typical waterfowl To encompass spring migration, we pro-
migration altitude, we then determined their grammed PTTs to last 6-8 months by using a
potential airspeed and compared it with the- repeating duty cycle consisting of a 5- to 6-hr
oretical values of and (Bruderer and transmission period followed by a 72-hr rest-
Boldt 2001). ing period; some PTTs lasted long enough to
METHODS provide data during fall migration. We used
the Argos location and data collection system
We captured pintails at the following times (Argos, Inc. 1996), including multi-satellite
and locations: (1) December-January 2000- service with standard and auxiliary location
2003 in California at Sacramento Valley na- processing, to monitor the locations of PTT-
tional wildlife refuges (NWR) and state wild- tagged pintails. Argos estimates PTT locations
life areas (central location: 39° 24' N, 121° from the Doppler shift in transmission fre-
58' W); (2) November-Janiiary 2001-2002 in quency received by satellites as they approach
the Playa Lakes Region of Texas at Buffalo and then mcwe away from the PTT. Argos
Lake NWR (34° 54' N, 102° 7' W) and on pri- checks the plausibility of locations via (1)
vate lands (33° 46' N, 101° 51' W), and along minimum residual crnn; (2) transmission fre-
the Texas Gulf Coast on a unit of Aransas quency continuity, (3) shortest distance cov-
NWR (28° 33' N, 96° 33' W) and on private ered since previous location, and (4) plausi-
lands (27°20'N, 97°48'W); and (3) Octo- bility ol velocity between locations. The num-
ber—November 2(K)1—2002 in New Mexico at ber of positive checks (NOPC; 0-4) is includ-
Bosque del Apache NWR (33°48'N, 106° ed with each location received via daily
366 THE WILSON BULLETIN • Vol. 117, No. 4, December2005
—
e-mails. The PTTs also provided sensor data corded during pintail migratory flights iden-
to index the unit’s temperature, remaining tified from multiple locations ofbirds heading
voltage, and motion. We used these, especially generally northerly or sou—therly during a sin-
the latter, to determine whether birds were gle transmission period concurrently with
alive and to verify that they were flying. PTT motion sensor data that suggested vig-
Argos classifies each PTT location based on orous activity. Additionally, we used only lo-
estimated accuracy and the number of trans- cations >200 km from the location recorded
missions (messages) received from each PTT on the previous or subsequent (or both) loca-
during a satellite overpass. The classes of lo- tion-days; these criteria precluded inadver-
cation quality (LC 3, LC 2, LC 1, LC 0) are tently including stationary pintails or those
based on >4 messages received by the satel- making only local flights.
lite via standard data processing; respective We selected only those points that best de-
accuracies are <150, 150-350, 350-1,000, fined the flight path, and deleted those that
and >1,000 m. Accuracy is expressed as the deviated from the general line of flight, re-
probability that 67% of the locations will fall versed direction, occurred in clusters (indicat-
within stated limits; therefore, high-quality lo- ing a stationary bird), occurred too close to-
cations might be inaccurate, while lower-qual- gether in space and time, or represented
ity locations might be very accurate (Hatch et movem—ent too fast or too slow between
al. 2000). Argos does not estimate accuracy points especially if LC was A or worse
of LC A (3 messages received), LC B (two (Hatch et al. 2000 used LC 0). For example,
messages received), or LC Z (latitude/longi- we considered a given point to be an obvious
tude often provided if >1 message received), outlier from the general line of flight if the
which are received via auxiliary processing; perpendicular distance from the flight line was
however, field tests have shown that LC A can greater than the average error distance from
be as accurate as LC 0 or LC 1 (Britten et al. true position as determined for the least ac-
1999, Hays et al. 2001), and LC B can be as curate LCs in recent field tests of PTTs (i.e.,
accurate or better than LC 0 (Hatch et al. 7.5 km for LC 0 and LC A, and 23-35 km
2000, Hays et al. 2001). Therefore, the accu- for LC B [Blouin et al. 1999, Britten et al.
racy of individual points along a flight path 1999]; 20 km for LC A and LC B [Hatch et
likely varies, even among those of the same al. 2000]; 1-10 km for LC 0 and LC A, and
LC (Hatch et al. 2000). If a PTT-tagged bird 7 km for LC B [Hays et al. 2001]). We also
is stationary (not flying), several criteria are considered points to be outliers ifthe time be-
normally used to choose one best location tween location points along the path was <10
from among the many normally provided by min and the distances between them <20 km,
Argos (Ely et al. 1997, Butler et al. 1998, Pe- unless this was typical along the flight path
tersen et al. 1999, Hatch et al. 2000). Because and produced similar intervening ground-
of continuous forward travel, however, Argos speeds among segments. We rejected one of
cannot provide alternate points at each loca- two points that created sharp-angled direction
tion for pintails in migratory flight. Therefore, changes (usually >45°) and reversals. Addi-
we initially plotted all locations of birds in tionally, we questioned the accuracy of indi-
flight and subsequently examined each of vidual locations ifthe groundspeed along path
them in detail to determine flight paths. segments seemed biologically impossible. We
We analyzed and displayed location data defined this as (1) >160 km/hr, the speed of
using Arcinfo and ArcView Geographic In- a Red-breasted Merganser (Mergus serrator)
formation System software (Environmental flying with a 32 km/hr tailwind, while being
Systems Research Institute, Redlands, Cali- chased by a small aircraft (Thompson 1961),
fornia). Eoreach female, we plottedindividual or (2) <20 km/hr when point separation was
flight paths using all PTT locations acquired <20 km, unless intervening groundspeeds
while the bird was flying. Each flight path matched those between other more widely
consisted of segments formed by successive separated points along the path. These criteria
pairs of adjacent location points (e.g., a path are somewhat arbitrary, but provided a con-
formed by five points would have four flight- sistent—method for selecting and rejecting lo-
path segments). We used only locations re- cations similar to procedures used by Hatch
Miller et al. • PINTAIL FLIGHT SPEED 367
et al. (2000), in which they discarded loca- We assumed that the weather charts repre-
tions “conspicuously outside” clusters of sented conditions at the location offlying pin-
points (stationary birds) because they violated tails, and we used wind speeds and directions
their redundancy rule. nearest to each pintail flight path (Shamoun-
We estimated apparent groundspeeds along Baranes et al. 2003). Because exact flight al-
each outlier-corrected flight path by summing titudes remained unknown, we did not add un-
the total time (hr) and distance (km) of each justified precision to the generally imperfect
flight-path segment, and then dividing total data to account for the angle at which tail-
distance over the flight path by total time from winds orheadwinds may have interceptedpin-
the first to the last accepted location point. We tail flight paths (Gill et al. 2005). Instead, we
used multiple flight paths from individual assumed that tailwinds and headwinds essen-
tagged hens, if available, and estimated tially paralleled flight paths, and ignored com-
groundspeed as mean ± SE for all flights. For pensation and drift (Wege and Raveling 1984,
comparison, we also estimated groundspeed Alerstam and Hedenstrom 1998). We calcu-
—
for all flights using all recorded locations (out- lated airspeeds either as (1) groundspeed
liers retained) to recognize our uncertainty tailwind or (2) groundspeed + headwind. To
with the deletions and determine how our cri- characterize migration conditions at the sur-
teria may have affected final groundspeed es- face, we obtained archived sky conditions and
timates. surface wind speed and direction at the time
We wanted to determine reliable airspeeds of flights from weather stations nearest the
for PTT-tagged pintails, but wind speeds in- flight paths (Weather Underground 2005).
crease and their directions change markedly
RESULTS
with increasing altitude (Kerlinger and Moore
1989, Ahrens 2000); in addition, we did not During 2001, 2002, and 2003, we obtained
know at what altitudes our tagged ducks mi- 21 flight paths of 17 PTT-tagged pintails for
grated (our PTTs did not have altitude sen- which we estimated groundspeeds (Fig. 1). Of
sors). We had no means to predict when or this total, 19 flights from 16 pintails occurred
where measurable flight paths would occur, during spring, and 2 flights from 2 birds oc-
and as a result, we could not a priori deploy curred during fall (1 hen provided 1 spring
radar and weather balloons to obtain ground- and 1 fall flight; Table 1). These data included
speed, wind speed, wind direction, and flight 14 pintails tagged in California, 2 in Texas,
altitude simultaneously, as done when birds and 1 in New Mexico. We used all original
pass predictable locations (Bruderer and Boldt Argos locations from 10 pintail flight paths
2001). Therefore, to assess the effect ofhead- (uncorrected), but deleted >1 location from
winds or tailwinds along the 21 pintail flight each of 1 1 others (outlier-corrected), because
paths, we assumed migration altitudes of sea they did not meet ourestablished criteria. Out-
level and 1,460 m above sea level (1,000 and lier correction resulted in increases in ground-
850 millibars [mb] at standard pressure; Ah- speed of 4-21 km/hr for five flight paths, de-
rens 2000), which is within the typical range creases in speed of 1-69 km/hr for five flight
used by migrating waterfowl (Kerlinger and paths, and no change for one flight path. Out-
Moore 1989, Berthold 1996), and for which lier correction reduced our total number of lo-
archived weather data were readily available. cations from 108 to 77. Correction for outliers
The higher altitude was used by Dau (1992), did not markedly increase the proportion of
wShamoun-Barancs et al. (2003), and Gill et al. high-quality locations forming flight paths
(2005) to examine migration of Brant, White compared with that in the uncorrected data
Storks (Ciconia ciconia), and Bar-tailed God- set. For example, the proportion of LC 1 and
wits (Limosa lapponica), respectively. We ob- LC 2 locations increased to 17% from 12% of
tained wind speed and direction on the dates all locations, and those (4' LC A, B, and Z
of pintail flights using North American Con- declined to 25% from 32% (no change in pro-
stant Pressure weather charts (850 mb) for portion of LC 0).
()():()() UTC and 12:00 UTC, published by the When we used the 1 I outlier-corrected
National Center for Environmental Prediction flights and the 10 uncorrected flights, ground-
(NCEP; National Climatic Data Center 2005). speeds of pintails along all 21 flight paths
368 THE WILSON BULLETIN • Vol. 117, No. 4, December 2005
FIG. 1. Migration flightpaths and path segments ofadultfemale Northern PintailsPTT-taggedinCalifornia,
Texas, and New Mexico, used to estimate groundspeed and airspeed (km/hr), 2001-2003. Circled uppercase
letters are bird identifiers from Tables 1, 2. Thick black lines show the measured flight paths divided into
segments by open circles representing pintail locations. Thin gray lines show migration routes prior and sub-
sequent to the measured path.
ranged from 40 to 122 km/hr (Table 1) and groundspeeds ranged from 45 to 111 km/hr
averaged 77 ± 4 km/hr (CV = 5.6, 90% Cl and averaged 78 ± 4 km/hr (CV = 4.9, Cl =
— 69-84). Two-thirds ofthe speeds (14 of 21 72-84), indistinguishable from the outlier-cor-
flight paths) occurred over a narrower range rected value. Groundspeed averaged 75 ± 4
of 61-80 km/hr. Without omitting outliers. km/hr (CV - 4.6, Cl - 70-81) for the 10
Miller et al. • PINTAIL FLIGHT SPEED 369
TABLE 1. Outlier-corrected groundspeeds ofadult female Northern Pintails, including start and end times,
distance flown, and time in flight, along flight paths determined via satellite telemetry, 2001-2003. All times
are Pacific Standard Time, except as noted. Bird identifiers (uppercase letters) correspond to those in Figure 1.
Distance Timein Ground
Start Start-end flown flight speed
Year date Bird Locationofflight(«i,«2)^ times (km) (hr) (km/hr)
2001 21 Mar A West-central Idaho (4, 4) 04:15-08:42^ 288.7 4.45 65
2001 25 Apr B West ofWashington/British Columbia 03:55-09:23 393.3 5.45 72
(8, 6)
2001 27 Apr C Northeastern Alberta (10, 5) 04:29-07:58® 267.4 3.49 77
2001 27 Apr D Western Alberta (4, 4) 19:31-00:38® 511.4 5.12 100
2001 3 May E West ofWashington/Oregon (4, 4) 02:30-06:23 309.2 3.90 79
2002 23 Feb F Northern California (8, 3) 17:05-20:06 212.6 3.13 68
2002 20 Mar G Southern Idaho (4, 3) 01:09-03:42® 294.4 2.55 116
2002 21 Mar Eastern Oregon to western Idaho 19:55-23:57® 257.8 4.03 64
(3, 3)
2002 13 Apr I North Dakota (10, 5) 15:54-19:52^ 180.1 2.28 79
2002 19 Apr J British Columbia coast (7, 4) 02:20-07:13 216.3 4.89 44
2002 21 Apr West ofWashington/British Columbia 11:51-15:46 157.6 3.91 40
(8, 5)
2002 24 Apr ML“ Western Oregon/ocean (3, 3) 23:17-01:25 292.7 3.79 77
2002 25 Apr Eastern Texas (3, 3) 20:41-22:20^ 218.3 3.06 71
2002 8 May Nb Central Alberta (3, 3) 21:08-22:49® 206.1 3.36 62
2002 9 May O Central Oregon (2, 2) 21:35-23:14 127.4 1.66 77
2002 14 May pb Southeastern Yukon (9, 5) 09:08-10:48 366.4 3.01 122
2002 26 May West-central British Columbia (4, 3) 22:47-02:15 277.3 3.46 80
2002 10 Oct Western Oregon/ocean (3, 2) 21:38-23:16 99.8 1.64 61
2002 12 Nov S Southern New Mexico to Mexico 18:49-22:17® 428.1 4.51 95
(6, 5)
2003 19 Mar T Northeastern Oregon (2, 2) 01:07-02:46 135.3 1.66 82
2003 31 Mar U Eastern Oregon (3, 3) 19:28-22:39 243.1 3.19 76
= total numberofseparatelocationpointsrecordedduringflightandusedtoestimategroundspeedwithoutcorrectingforoutliers;nj = number
ofacceptedlocationpointsusedtoestimateoutlier-correctedgroundspeed.
Superscriptsofthesameletterindicatemultipleflightsforthesamepintail.
®MountainStandardTime.
^CentralStandardTime.
uncorrected flights, 78 ± 8 km/hr (CV = 10.1, data), and the fourth flight (bird N) would
Cl = 65-90) for the 1 1 outlier-corrected have had headwinds of 6-9 km/hr. Corre-
flights, and 80 ± 7 km/hr (CV = 8.4, Cl = sponding airspeeds of pintails at 850 mb
69-91) for the 1 1 flights when not corrected ranged from 24 to 97 km/hr in tailwinds and
for outliers. Most (19 of 21) flights occurred from 59 to 80 km/hr in headwinds (Table 2),
partially or entirely at night (Table 1), and two with means of 55 ± 4 km/hr (CV = 7.9, Cl
paths transited land and sea (Fig. 1). = 48-62) in tailwinds and 71 ± 4 km/hr (CV
Based on wind speeds and directions at = 6.2, Cl = 64-78) in headwinds. The ratios
m
1,400 (850 mb), 17 of the 21 flights (81%) of groundspeed to airspeed averaged 0.73 ±
occurred in tailwinds and four in headwinds 0.6 in headwind (CV = 8.2, Cl = 0.63-0.83)
(Table 2). Groundspeeds averaged 82 ± 4 and 1.61 ±0.14 in tailwind (CV = 8.5. Cl
km/hr (CV = 8.2, Cl = 75—89) in tailwinds = 1.39-1.83).
and 53 ± 6 km/hr (CV = 1 1.8, Cl = 43-63) riie longest distance flown by a pintail for
in headwinds. Three of the four flights that which we est—imated groundspeed (bird B),
occurred in headwinds at 850 mb (birds A, J, was 2,926 km from Goo.se Lake in southern
and K; Table 2) would have had tailwinds Oregon (42° 15' N, 120° 23' W) to the Kenai
near the ground surface of 6-13, 7-11, and Peninsula in Alaska (59°12'N, 151°46'W;
13-15 km/hr, respectively (weather station Fable 1). Assuming that pintails flew at the
.
370 THE WILSON BULLETIN • Vol. 117, No. 4, December2005
TABLE 2. Airspeeds of adult female Northern Pintails estimated using satellite telemetry and supporting
wind speed and direction data from North American Constant Pressure weather charts (850 millibars or 1,460
m), 2001-2003. Local sky and surface wind direction categories at weather stations nearest to flight paths are
also given. Bird identifiers (uppercase letters) correspond to those in Figure 1.
Ground- Highest Wind Localsky
speed windspeed direction Wind Airspeed conditions;surface
Year Date Bird (km/hr)^ (km/hr)'^ (compass)'^ category‘s (km/hr)^* windcategory^
2001 21 Mar A 65 9 NW QHW 74 MC; QTW'
2001 25 Apr B 72 37 ssw QTW 35 OC; QHW2
2001 27 Apr C 77 19 ssw QTW 58 OC; QTW3
2001 27 Apr D 100 28 ssw QTW 72 MC; none''
2001 3 May E 79 46 ssw QTW 33 PC; QTW2
2002 23 Feb F 68 19 SSE TW 49 OC; VAR5
2002 20 Mar G 116 19 w TW 97 CL; QTW6
2002 21 Mar Hf 64 28 SW QTW 36 CL; QHW"
222000000222 211139 AAAppprrr JIKg 447940 221889 WNSNWNWW, N QQHTHWWW 755129 LMPCRC;;;TQQWTT^WW'9«
2002 24 Apr Lh 77 19 SW QTW 58 CL; VAR"
2002 25 Apr M 71 28 WSW, SW QTW 43 MC; QHW'2
2002 8 May Nf 61 19 N HW 80 OC; HW^
2002 9 May O 77 9 SE TW 68 OC; HW'3
2002 14 May P' 122 56 SE TW 66 LR; QTW'^
2002 26 May Qg 80 56 SSE TW 24 LR; QTW'5
2002 10 Oct Rh 61 9 NW, NNW TW 52 OC; none"
2002 12 Nov S 95 28 NNW, N QTW 67 CL; QTW'^
2003 19 Mar T 82 19 SSW TW 63 CL; QTW'"
2003 31 Mar U 76 9 SW QTW 67 R; QTW'«
h^VSWayilmnubdeoslsspreofeuodnrsderaednladttoicvnoeemawpriaenssdtskddimir/reehccrttiifoonrnoscmaotbTetagaboilrneyed1apfprloymtaoiruspppeeerd/adiirreacntdiosnursfyamcbeodlastao:nQ85=0qmuabrtceornisntga,nTtWpre=ssutraeilwwienadt,heHrWcha=rtshenaedawriensdt,piSntWail=flsiigdhtesw.ind,
VAR = variable,none = calm.
Airspeed= groundspeed-tailwind,orgroundspeed + headwind;windspeedusedisthehighestoftherangesobtainedfromweathercharts,
Ds31ah4k=eoo=wStFkaotWy;rhatetc9oScsnomo=dninidttVihLiat,oaninkcoNsenoo:,urlvtOYeehauCrswk,teos=fnBtar;vioTotve1irer5sarrhbcil=atCeosortTifl,eeoursrLmr;baRm4ciiega=,r=;aBtlE1riii0dogthmnit=.osnhrNQtauCiuoniomn,llb,luReamAryblue=ibtdeaerr,;astiuaWn1p;a,6esr5Mhs=ic=CnrTigrRpt=uteotsdnhmd;roieosnfr1tge1rl,Cyot=CnoacsllNteioheqfeuwoudprneyonen,iracartPe;e,sCs6,tO=rw=NeeegapBowaturnhrt;elMlereyy1xs,2citlcaIo=todui;aodChnyoo:1,;l7l1C7e=L=g=eHB=eSoOrtincamstltieaeis,raotirnI;oo,d,nwaT,OhheorxeO;earrsgee2;ogno>=1;n13;H8co=1o=q8nuRdJi=eiaatdmmimBeo,ounsnmWtadsaops,,wphnlOiO,irnregeNed,tgogooorwnnnte;.;h
Superscriptsofthesameletterindicatemultipleflightsforthesamepintail.
average outlier-corrected groundspeed of 77 Canada Geese (Branta canadensis) fitted with
km/hr, they would have required 38 hrto com- VHP radio-transmitters migrated at ground-
plete the flight nonstop. speeds of 49-110 km/hr (Wege and Raveling
1984). Bellrose and Crompton (1981) clocked
DISCUSSION migrating Canada Geese at 61-73 km/hr.
The estimated 77 km/hr migration ground- Lesser Snow Geese {Chen caerulescens) at
speed ofPTT-tagged adult female pintails was 67-83 km/hr, and Mallards {Anas platyrhyn-
consistent with that of the upper range ofpin- chos) at 72 km/hrby following in automobiles
tail groundspeeds (local flights) estimated us- or aircraft. Using satellite telemetry, radar, and
ing radar (65-76 km/hr; Bruderer and Boldt other means, migrating Brant have been re-
2001). Average groundspeeds of other ducks corded at groundspeeds of 99 km/hr (Dau
during local flights have ranged from 42 to 1992), 90 km/hr (Lindell 1977 cited in Eb-
116 km/hr (Speirs 1945, Lokemoen 1967, binge and Spaans 1995), 30—115 km/hr
Kerlinger 1995, Bruderer and Boldt 2001), (Green and Alerstam 2000), and 58-109 km/
very similar to the range we obtained for mi- hr (Green et al. 2002). Wide interspecific var-
grating pintails. During migration, PTT-tagged iation in these reported groundspeed estimates
Whooper (Cygnus cygnus) and Tundra (C. probably resulted from species-specific flight
columbianus) swans migrated at 60-90 km/hr aerodynamics (Pennycuick 1975, Rayner
(Pennycuick et al. 1996a, Ely et al. 1997), and 1990), atmospheric conditions (Kerlinger and
Miller et al. • PINTAIL FLIGHT SPEED 371
Moore 1989), and errors associated with the erage pintail airspeed support the hypothesis
various methods (Bruderer and Boldt 2001). that their airspeed was faster, and groundspeed
The relatively wide range of pintail ground- slower, in headwinds compared with tail-
speeds in our study undoubtedly reflected pri- winds. The ratios of groundspeed to airspeed
marily wind conditions, and perhaps angle of for tagged pintails show that compared with
flight (ascending, descending, horizontal; still air (ratio = 1.0), pintails decreased their
Green and Alerstam 2000); however, the close groundspeeds about 27% in headwinds and in-
agreement between outlier-corrected and un- creased groundspeeds by about 61% in tail-
corrected data suggests that measurement er- winds, suggesting that migration occurred at
ror was minimal. We recommend that inves- Vmr- Demonstrating such compensation during
tigators report groundspeeds and groundspeed local flights. Tucker and Schmidt-Koenig
to airspeed ratios because of their implication (1971) reported a pintail airspeed of 56 ±
1
in analysis of flight range and cost. km/hr with tailwinds and 66 ± km/hr
1
Birds use tailwinds to minimize the ener- against headwinds, similar to our results (55
getic cost of migration by increasing ground- and 71 km/hr, respectively). Because Tucker
speed and range, reducing airspeed to main- and Schmidt-Koenig (1971) did not report re-
tain groundspeed, or both (Richardson 1990, spective groundspeeds or wind directions, we
Alerstam and Hedenstrom 1998), and this has estimated groundspeeds from their study by
been verified for migrating waterfowl (Blok- using their reported average wind speeds of
poel 1974, Bellrose and Crompton 1981, 18 and 31 km/hr and applying them as tail-
Wege and Raveling 1984, Dau 1992, Green et winds and headwinds. This produced potential
al. 2002). Most pintails (had they migrated at respective groundspeeds of 74 and 87 km/hr
our specified altitude of 1,460 m) would have in tailwinds and 48 and 35 km/hr in head-
benefited from tailwinds, as exemplified by winds, similar to our findings.
their average higher groundspeed and lower Using the theoretical flight models of Pen-
airspeed in tailwinds. Birds are known to alter nycuick (1989) and Rayner (1990), Bruderer
flight altitudes and move to those with favor- and Boldt (2001) calculated and for
able winds (Gauthreaux 1991). If three of the pintails as 64 and 40 km/hr, respectively. The
four pintails in our study that we assumed average airspeed of our pintails in tailwinds
were flying into headwinds aloft had instead (55 km/hr) was above V^p and below and
been flying near the ground surface, they their average airspeed in headwinds (71 km/
would have had tailwinds. Also, the three hr) was greater than both V^p and In four
flights occurred partially or completely during instances, our pintails flew more slowly than
the day (Table 1), when low-altitude migration in tailwinds (24-36 km/hr), and on nine
flights are typical (Richardson 1990). How- flight paths in variable wind directions, they
ever, we cannot be sure of the migration alti- flew faster than (66-97 km/hr); on eight
tude, and sky conditions observed from the paths, pintails flew at speeds between the the-
ground varied from mostly cloudy to light rain oretical speeds (43-63 km/hr; Table 2). Our
and overcast (Table 2), weather types that tend data support Welham’s (1994) findings that
to discourage migration (Richardson 1990). pintail-sized birds tend to migrate at but
Birds generally adjust airspeed when wind are not bound by theoretical flight models
direction changes; waterfowl increase air- (Pennycuick 1998); more data are needed to
speed to compensate for headwinds and re- compare field results with their predictions.
duce airspeed as tailwinds increase (Tucker The four excessively slow speeds in tailwinds
and Schmidt-Koenig 1971, Bellrose and (<Knp) reflect errors resulting from over-
Crompton 1981, Wege and Raveling 1984, estimation of wind speed (Tucker and
Pennycuick et al. 1996a), but the adjustments Schmidt-Koenig 1971), resulting from poten-
are not necessarily proportionate (Bellrose and tial ditferences between winds at the actual
Crompton 1981). Our pintails clearly did not (unknown) and .selected (850 mb) flight alti-
have a strategy to maintain airspeeds in tudes. Pintails probably do not fly at the the-
changing wind conditions (Table 2), although oretical minimum power speed in any event,
Blokpoel (1974) concluded that migrating a phenomenon demonstrated for a Common
Lesser Snow Geese did. Our estimates of av- Teal {Anas crecca crcccci) and other birds that
372 THE WILSON BULLETIN • Vol. 117, No. 4, December2005
refused to fly in wind tunnels at (Penny- relatively large sample sizes. Average ground-
cuick et al. 1996b). To address this problem speed estimated using all data did not differ
in future field studies, wind speeds and direc- from that using outlier-corrected data, even
tions will need to be obtained very near flight though the former included very high and un-
altitudes because wind data gleaned from con- realistic speeds on six flight-path segments
stant pressure charts are only as relevant as (175, 381, 484, 611, 829, and 999 km/hr).
the selected flight altitude. Investigators could These did not affect the average because they
use PTTs with onboard altitude sensors, but occurred over very short time periods between
these sensors are not yet available for the the first and last location points (32 sec to 7.2
small PTTs required for use on pintail-sized min), and because we did not estimate
birds. Larger PTTs with GPS technology are groundspeed by averaging speeds of each
available, which would be suitable for geese flight-path segment. Investigators could in-
and swans; these can track position, altitude, crease the frequency of high-quality locations
heading, and speed with high accuracy (±30 (LC > 0) by increasing PTT power, or, for
m; Microwave Telemetry, Inc. 2005). large species, adopt new PTT models that in-
Most waterfowl are known to migrate at corporate global positioning systems (GPS;
night as well as during daylight hours (Bell- Microwave Telemetry, Inc. 2005). This would
rose 1980, Kerlinger and Moore 1989). There- improve estimation of groundspeeds and air-
fore, it is not surprising that nearly all of our speeds and their precision along individual
measured flights of tagged pintails occurred flight-path segments.
partially or entirely at night. For long-distance Back-mounted PTTs may have reduced our
migrations, typically beginning after sunset estimates ofpintail groundspeed; however, re-
(Kerlinger and Moore 1989), travel may ex- sults from previous studies that addressed this
tend into daylight hours because there is not issue have been inconclusive. For example,
5%
enough time to make the transit during night- Butler et al. (1998) estimated a potential
time hours (Berthold 1996), or wind condi- increase in the energetic costs offlight ofBar-
tions might favor continuing into daytime nacle Geese {Branta leucopsis) outfitted with
hours (Liechti and Schaller 1999 cited inJenni 33-g PTTs. Because geese are able to reposi-
and Schaub 2003); five ofour recorded flights tion PTTs under their body feathers while
overlapped day and night (birds A, B, C, E, preening (Butler et al. 1998), wind resistance
and J; Table 1). Migration in the cooler, am- due to PTTs may be reduced (Obrecht et al.
bient nighttime air at moderate to high alti- 1988). Harnessed transmitters increased the
tudes theoretically provides bioenergetic ben- energy cost of rapid flight in homing pigeons
efits of heat dissipation and water conserva- (Rock Pigeon, Columba livia\ Gessaman and
tion through evaporative cooling (Berthold Nagy 1988), perhaps due to the vertically flat-
1996, Kvist et al. 1998). This could be critical tened posterior ends of the test transmitters
for waterfowl during long, nonstop migrations (Obrecht et al. 1988). In wind tunnel experi-
when diurnal and surface temperatures are ments that tested the aerodynamic character-
high (e.g., early fall, late spring). Nocturnal istics ofthree transmitter sizes attached to fro-
atmospheric conditions provide distinct ad- zen Lesser Snow Geese and Mallards, stream-
vantages to migrating birds, including cooler lined transmitters created the least drag, and
temperatures and more humidity, denser air, the smallest test transmitters (slightly larger
weaker and more laminar horizontal winds, than our 20-g unit [excluding harness]) cre-
and little or no vertical air motion compared ated drag too small to be measured (Obrecht
with daytime conditions (KerlingerandMoore et al. 1988); the sloped anterior and posterior
1989, Ahrens 2000); these conditions maxi- ends ofourpintail PTTs mimickedthe stream-
mize flight speed while reducing energy cost. lined shape of these units. Pennycuick et al.
Additionally, night migration would enable (1996b) recently reduced their estimate of
celestial navigation (Bellrose 1980). body-drag coefficients for flying birds from
Our data suggest that researchers need not 0.4 to 0.08, suggesting that drag may not be
delete any but the most obvious outliers to as important as once thought. Based on this
estimate groundspeeds when using the method new information and our typical mean
of total distance divided by total time with groundspeeds and airspeeds of PTT-tagged
Milleret al. • PINTAIL FLIGHT SPEED 373
pintails, we conclude that the variation in speedsofthreewaterfowl species.WilsonBulletin
groundspeed caused by wind direction and 93:121-124.
speed likely overwhelmed wind resistance and Berthold, P. 1996. Control of bird migration. Chap-
mass effects of PTTs. Nonetheless, we en- man and Hall, London, United Kingdom.
pcloaunrtaagbelerePsTeTarschfeorrs mtoodedreavteelloyp rseilzieadblew,atiemr-- BlokdBpiloauenel,WGielHed.slei,f1e97pSa4er.trvMi1i.cgeRr,eaOpttoitroatnwaSo,efriOLenest,sasrneioro.,S2Cn8a,onwaCdaana.an-d
fowl because of potential aerodynamic bene- Blouin, F, j. F. Giroux, J. Ferron, G. Gauthier, and
fits and reduced energetic costs of flight. G. J. Doucet. 1999. The use ofsatellite telemetry
to track Greater Snow Geese. Journal ofField Or-
ACKNOWLEDGMENTS
nithology 70:187-199.
We thank A. A. Marnell, II, and the Tuscany Re- Britt1e9n9,9.M.PerWf.o,rmPa.ncL.e Kaenndneadccyu,raacnydevSa.luAamtibornosseo.f
search Institute for providing all operational funding small satellite transmitters. Journal of Wildlife
to support the California work through annual grants Management 63:1349-1358.
to Ducks Unlimited, Inc., Memphis, Tennessee, and Bruderer, B. and a. Boldt. 2001. Flight character-
astuipopno,rtSiancgragmraennttso,toCtahleifCoranliiaf.ornDi.aPWatCeornfnoelwlly,AssF.ocAi.- Iisbtiiscs14o3f:b1i7r8d-s:20I4..Radar measurements of speeds.
RDe.iJd.,Baatntd, MG.. PLe.trSiet,ewaanrdtGs.ecS.urYeadrrtihsemfaunnadginegd,daonnadteBd. ButlBere,haPv.iJo.u,rA.anJ.dWpohaykseisol,ogayndofC.SvMa.lbBairsdhoBpa.rn1a9c9l8e.
Rfuenidds,.GB..S.D.YaJr.riBsa,ttM,.M.G.PAetnrdiee,rsDo.n,P.K.CoLn.neGlulyy,n,F.anAd. gGreaetsioen.BrJaonurtnaalleoufcoApvsiiasnduBriionlgogtyhe2ir9:a5u3t6-u5m4n5.mi-
o(Dt.RheeCgr.iopDnluan2n)cn,ianTnge.xcoaTnsthrePiabrUuk.tsSe.datnFodisphWrioljadenlcditfedW,eilvadenlldiofpetmheeSnetPrlvaainycdae Caccbnaiamrimdsis.ec,WibDal.ssioFs.nafBnourldleRst.eilneSc.9t7iH:neg3d0i6nt-.r3a1n1s89m.8i5t.teArnloaaedrsodyi-n
aLnadkeNseJwoinMtexViecntourweorpkr.ovP.idHeodwfeuyndpirnogvifdoerdthteechTneixcaasl Carnceayt,ionS.oMf.du1c9k9s2.usSipnegciewsi,ngagep,luamnadge.sexU.iSd.entFiifsih-
assistance. P. Blake, D. Campbell, N. M. Carpenter, S. and Wildlife Service, Washington, D.C.
ctCeaoctrhedndeiscp,iianCnt.asilDwehncoanpitstu,rraeJp.pesGid.tedsM.uecnWksseika,tnhdaannakdssiJt.shteAe.dmawMinotyohnPfiTelolT-d Dau,dBirCte.inotnP.s.B1r9Wa9in2lt.dafTobhweerlnfi4ac3lll:a8m0ii-ng9rr5ae.tliaotnionoftoPaccliifmicatFilcycwoany-
aSA.t.tBaLucarhunmgeethntlt,i,nC,e.sapJ.encdGiraDel.gloyLrC.y.,LLaoenuedg,hLBm..aLnB.a.lWliJa.lrldKi,.aSm.DsaCmuogarhdnetarsg,teyJd,. Ebbinogfeb,odB.y Sr.esaernvdesB.acScpuamaunlsa.ted19i9n5.spTrhiengismtpaogritnganacre-
Ja.llBastatt,ellBi.teM.datBaa.llWared,tRh.anRk. CS.oxE,.aSncdhtwharrezebaancho,nyBm.ouDs. eliaesdiBnrtehnettGeemepseera{tBerzaontnae bfeorrnbirceleadibenrgniicnldaa)rki-nbethle-
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Ely, C. R., D. C. Douglas, A. C. Fowler, C. A. Bab-
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