Since the spring migration of hummers seems to be finally winding down, perhaps now would be an appropriate time to assess it.
I have long
theorized speculated that the northward migration of Archilochus hummers (i.e., Ruby-throats and Black-chins, the only species we in south Texas generally see) follows the appearance of one of their favorite forage flowers, the Indian Paintbrush (Castilleja indivisa).
This plant commences to bloom in wave-like fashion, from south to north, beginning in mid-February; north of San Antonio the peak season seems to occur in April. 1 In "normal" years here in Atascosa County (ca. 30 miles south of San Antonio), the first Indian Paintbrushes begin blooming in late February and are in full swing by mid-March--coincidentally about the average arrival times for Archilochus types. 2
This year, however, with all of south Texas in the grip of an extended drought, the extent of the Castilleja bloom has been significantly reduced. Instead of acres and acres of mixed Bluebonnets (Lupinus subcarnosus and L. texensis) and Indian Paintbrushes, these have managed to grow only in occasional small clumps composed of several individual plants. My own half-acre backyard, for example, usually tinted red with Paintbrushes, this year contains fewer than twenty plants.
Thus I speculated that our first Archilochus hummers would be late, slowed by the lack of forage blooms en route. Wrong! The first Archilochus appeared at a feeder on the morning of 9 March, which seemed to be quite typical, neither unusually early nor unusually late. I couldn't determine whether it was a Ruby-throat or a Black-chin, for it was gone from the feeder in a flash. Either species is equally likely for the FOS [first of season].
If our first hummer was a trans-Gulf migratiing Ruby-throat, this would explain why the paucity of flowers hadn't slowed him down--the FOS is always a "him." I suspect, however, that most of our early season Ruby-throats arrive by an overland path similar to that followed by their Black-chinned congeners. Speculating again; I have no proof of this.
Perhaps then, if the dearth of flowers failed to slow down the migrating hummers, it is possible that it sped them up! Any bird capable of flying non-stop across the Gulf of Mexico from the Yucatan would not be daunted by the depth of south Texas. But, again, they weren't exactly early either. Williamson (2001) places the average arrival dates for Ruby-throats in south Texas between 1 March and 11 March, with the same dates applying to Black-chins as well. 2
The Black-chinned is the local resident breeding species; Ruby-throats are merely passing through on their protracted spring migration. Nevertheless, Ruby-throats continue trickling through this area until about the beginning of May. Although I know of no Atascosa County, Texas nesting records for the Ruby-throat, I see no reason why they shouldn't nest here; the extensive live oak savannas somewhat resemble their preferred eastern forests.
Our first female hummer appeared exactly ten days later, on 19 March. Again, it was difficult to determine which species I was seeing at any given time. I mainly distinguish female Archilochus by the intensity of the green on their backs. The female Ruby-throat typically has a much brighter shade of green on the back, whereas the female Black-chinned appears a much duller shade, sometimes almost gray. This is a somewhat subjective criterion, but if the light is good it usually works for me.
At any rate, many of the duller-colored females seemed to immediately begin gathering nesting materials, especially dandelion seed filaments. Given that they may produce as many as three broods before they depart in August, the local resident females apparently get down to business quickly.
The paucity of wildflowers has also caused an unusual springtime concentration of hummers around our sugar-water feeders. From late March onward it has been rare to glance at a feeder and fail to see several birds, either feeding at a port or hovering, impatiently awaiting their turn. In "normal" springs I will typically observe four or five hummers feeding at Paintbrushes in the backyard for every one actually using a feeder. This spring, however, it is not unusual--especially in the morning or during the evening "frenzy"--to see every port occupied by a bird, with half a dozen or so hovering about. Considering that we keep seven feeders going throughout the warmer months, this would indicate nearly a hundred individuals present in the area at such times. Hummingbird banders, however, assert that counting the number of birds visiting feeders results in a substantial underestimate of the number actually present.
Thus far the only unusual hummer to visit during migration was an adult male Rufous Hummer (Selasphorus rufus), which appeared over the weekend of 1-2 April. Rufous hummers are not at all uncommon here during the summer/fall migration or even as overwintering birds. This was the first time, however, I have noticed one during the spring--most overwintering Selasphorus have departed several weeks before the FOS Archilochus types appear in March. The male Rufous in the photo below is not the one who visited here, but instead one from last summer in New Mexico.