|Twenty-two Years of
Ruby-throated Hummingbird Migration at Holiday Beach Conservation Area,
[Originally published in Ontario
Birds 16: No. 3 (Dec. 1998),
This paper presents both data and observations regarding the migrations of Ruby-throated Hummingbird (Archilochus colubris) at Holiday Beach Conservation Area, Essex County, Ontario, Canada, in order to provide an understanding of their movements in the region. Data was obtained from many dedicated individuals, whose participation was requested in addition to their duties as hawk counters. The data spans twenty-two years, from 1976 to 1997. Ellie Cox provided the data from 1976, and from 1977 through 1982 the author was the sole source of data. From 1982 to the end of the season in early October 1997, observers from the Holiday Beach Migration Observatory, and others, were largely responsible for the daily tallies, which have been compiled by the author. Data associated with specific hours and weather conditions prior to 1990 are entirely the author's. Data from more than 9,000 birds are included in this study.
Study Site and Methods
Holiday Beach Conservation Area is located in extreme southwest Essex County in extreme southwest Ontario, Canada (see map, figure 1), about 5 kilometers south-southeast of Amherstburg. The northern edge of the park is bounded by Essex County Road 50, the west edge by the eastern side of the mouth of Big Creek, the east edge by farmland and the south edge by Lake Erie. Habitats present include lakeshore, freshwater marsh, open deciduous woodland (mainly maple and cottonwood) and open areas (parking lots). There are some pines and cedars near the northern end of the park.
Figure 1. Holiday Beach location (2) and some hummingbird migration routes through the area.
This area has long been known as a hawk migration site and the data contained in this study were obtained in addition to the hawk count by volunteer observers. Data concerning weather were gathered from that taken for the hawk count. In order to maximize the view of the sky, the main site for counting is a parking area at the southwestern corner of the park. Hummingbirds were counted, hour by hour, as they flew past the ground-based observer(s) from 1976 - 1988. From 1989 - 1990, the newly erected observation tower (13 meters tall) was used for counts. Care must be taken to distinguish the rapid and difficult-to-detect hummingbirds from the migrating dragonflies and large bees also flying through. All observers were experienced enough to make this distinction. Coverage was most consistent from 1983 - 1997 (see figure 2).
Figure 2. Annual observer effort between 15 Aug. and 12 Oct (1976 - 1997).
Annual Cycles of Migration
After an initial low period from 1976-1979, when there was also low observer effort, the annual totals appear to be cyclical. Figure 3 shows a two year cycle of high and low numbers between 1981 and 1988. From 1988 to 1991 the cycle appears to have leveled off, but this could be due to the effects of observers adjusting to counting from the new hawk tower at 13 meters above the ground.
Figure 3. Annual Ruby-throated Hummingbird totals at Holiday Beach (1976-1997).
Seasonal Migration Pattern
Ruby-throated Hummingbirds have been detected at Holiday Beach from
August 18 to October 11. Evidence from other sites indicate that adult
males can begin migration as early as late July, but efforts to locate
adult males, or migration earlier in August, have thus far been
unsuccessful. Since the birds rarely are observed hovering or feeding,
there is little likelihood that any data regarding differential
migrations based on age or sex classes will be possible without
conducting banding studies at the site. It is possible, given a good
view, to distinguish an adult male in flight as it passes the observer,
but to date there have been very few reports. The male birds may take
different routes. Incidental catches of hummingbirds at nearby
Metrobeach Metropark, Macomb Co., Michigan (pers. obs.), implies a
pattern of adult females followed by immature males, followed by
immature females. The pattern of seasonal occurrence shown in figure 4
hints at a possible dual peak of numbers, one around September 5 and
another around September 15. These peaks may coincide with the adult
females and immatures of both sexes, respectively, although this is only
speculation in the absence of banding studies. Very few adult males have
ever been identified during the migration study at Holiday Beach. It is
interesting that there have been hummingbirds through in October
annually since 1984 (total of 54 birds, 0.59% of the total). The data
from Hawk Mountain, Pennsylvania (Willimont, Senner, and Goodrich 1988),
does not show any migration into October.
Figure 4. Daily abundance of migrating Ruby-throated Hummingbirds at Holiday Beach(Composite of all data from 1976-1997)
Daily Migration Pattern
Data from Hawk Mountain (opt. cit.) portrayed the daily rhythms of hummingbird migration as limited in the morning, typically not beginning until 1000h. (E.S.T.) and finishing before 1400h. This was attributed to the birds' apparent need to warm up in the morning before commencing migration. The data from Holiday Beach (with an average of 5 times as many birds per season as Hawk Mountain) shows a much wider range of migration time (figure 5). The earliest birds were through between 0500h and 0600h and the latest were through between 1700h and 1800h. In fact, as shown in figure 6, 38% of all hummingbirds at Holiday Beach migrated before 1000h! The difference in the two sets of data may be attributable to the higher altitude of the Hawk Mountain site, as Holiday Beach is at roughly 650 feet (195 m) above sea level, and is in an extremely flat area of southwestern Ontario. Conditions on Hawk Mountain may be colder during the bird's migration period, requiring longer morning "warm-ups." The October records from Holiday Beach are mainly of birds seen in the afternoon.
Figure 5. Hours of Ruby-throated Hummingbird migration at Holiday Beach
(Data collected principally by the author from 1983 - 1990).
Figure 6. Percent of Ruby-throated Hummingbirds accumulated by hour
(same data as figure 5).
Migration Pattern Relative to Wind Direction
As at Hawk Mountain, there was a strong correlation with northwest and west winds with peak migrations of hummingbirds (Figure 6). The large peak on southerly winds on figure 7 is due to an apparently anomalous single day where 520 birds passed in one afternoon! Factoring this day out, there were only 38 birds that passed on southerly winds.
Figure 7. Number of birds by wind direction (same data as figure 5 & 6).
Once the birds have flown out of the woods and are heading across the parking lot to be counted, there is little to distract them. Artificial red flowers placed on the tower in 1990 only caused about 5% of the birds to pause. Natural food items were present in the medians between parking lanes (through 1996, when many lanes were removed for construction of a pond). Only about 5% of all birds (estimate) have ever been observed to pause in these areas. The plants fed upon at these times include (in order of occurrence) Purple Loostrife (Lythrum salicaria), Small White Aster (Aster vimineus), and once from Turtlehead (Chelone glabra). On the edge of the open woodland are stands of Spotted Jewelweed (Impatiens capensis), where birds have been seen occasionally feeding prior to striking out across the open areas.
Laboratory studies of the bioenergetics of flying hummingbirds made to determine their ability to cross the 500 mile wide Gulf of Mexico have, necessarily, concentrated on hovering birds enclosed in bell jars (Odum, Connell, and Stoddard 1961, Lasiewski 1962). The actual flying style of migrating birds is quite different, and may extend significantly, their flying range (pers. obs.). Birds have been consistently observed to flap vigorously for about 1 second or more, followed by a period of "free fall," where the wings are either folded or not flapped, for about 0.5 seconds or more. This gives the birds a somewhat bounding flight style, and the technique is used at all altitudes thus far observed. This technique is known to conserve energy in woodpeckers and other species (Tobalske 1996), but has apparently not been described previously for the Ruby-throated Hummingbird.
Published flight speeds of A. colubris have ranged from 40 to 80 km/hr. On September 8, 1980, I measured two distances on frequently used flight lanes. One was 15 meters and was between the vegetated medians between parking lanes. The other was 21 meters. A stopwatch was used to time the birds as they flew between these measured lanes. The birds were able to be detected momentarily before reaching the starting point. Times were obtained ranging from 26 km/hr. against an 8 km/hr headwind to 63 km/hr. with an 8 km/hr) crosswind. Data from the 5 timed flights are shown below in Table 1.
Table 1. Flight speeds of Ruby-throated Hummingbirds at Holiday Beach.
Altitude of Flight
Altitude of flight data was collected only for 1990 from the volunteer hawk counters that year. Observations were done from the top of the tower (13 meters tall). Birds are rarely, if ever, observable below eye level from here. They blend in with the vegetation and their size and direct flight make them extremely difficult to detect under these circumstances. About 90% of all birds noted in 1990 were from 2 - 5 meters overhead, or 15 - 18 meters above the ground. About 4% were over 5 meters overhead, up to a maximum of about 30 meters, which may be as far as hummingbirds in flight can normally be detected. Rare individuals (~1%) were picked up in binoculars and could have been 50 meters or more overhead. This data could be misleading, as it may represent observer location more than true altitude of flight. Data from ground-based counts prior to 1990, although lacking, can be estimated based on my 22 years of experience. About 80% came through from eye level to 10 meters overhead, 18% came through from 10 to 30 meters overhead, and 2% were detected only in binoculars 30 meters or more overhead.
All humingbirds that were observed migrating past the site were flying from east to west, parallel to, and about 20 - 300 meters north of the shore of Lake Erie (Figure 1). It is interesting to note that the birds seemed to be exhibiting the same "water avoidance" behavior as the hawks during their migration. One observer (pers. com.) has commented that this pattern, combined with the scarcity of Ruby-throated Hummingbird in the Yucatan Peninsula of Mexico (des Montes 1988, Loftin 1991, pers. obs.), suggests that far fewer birds may actually attempt the crossing of the Gulf of Mexico than is currently assumed. Studies to date have concentrated on the bioenergetics pertaining to whether Ruby-throated Hummingbirds could make the crossing (Odum et al. 1961, Lasiewski 1962). Another observer (A. Wormington) has noted numbers of Ruby-throated Hummingbirds leaving the southern tip of Pt. Pelee (east of Holiday Beach, see figure 1) in the fall, so birds do cross the lake. The maximum water crossing from this point to Pelee Island is about 30 kilometers, where they can then hop another 30 kilometers to Kelley's Island (where birds have been noted in mid-August - pers. obs.), then on the final 30 kilometers to the southern shore of Lake Erie in northern Ohio. Near Holiday Beach, the crossing is more on the order of 60 kilometers, but this is far short of the 500 miles (850 km) across the Gulf of Mexico! Studies of trans-Gulf migration published in the literature (Bullis 1954, Bullis & Lincoln 1952, Lowery 1946, Paynter 1953, Siebenaler 1954, Stevenson 1957, Van Tyne & Trautman 1945, Williams 1945, 1948, 1952) only contain about a dozen sightings of Ruby-throated Hummingbirds. This bird is very numerous in coastal Texas in September and October (Stokes & Stokes 1989, pers. obs.), so the magnitude of Ruby-throated Hummingbird migration that crosses the Gulf of Mexico could be a very small proportion of the species' migration as a whole.
I wish to thank the numerous hawkwatchers who divided their attention from the primary task and contributed data to this study over the past 22 years. I also thank Paul Pratt for providing the data for the 1997 season, and Alan Wormington and Laurie Goodrich for helpful discussions that resulted in ideas presented in this paper.
Baumgartner, A.M. 1989. Ruby-throated Hummingbird Populations
in Northeastern Oklahoma - 1977-1988. North
American Bird Bander, October-December: 115-117.