Focus On...The Lesser Nighthawk
The Lesser Nighthawk (Chordeiles acutipennis) is the southernmost of California's three widespread nightjars. Primarily a bird of the lower deserts, this graceful aerial insect feeder appears to have a disjunct coastal population. Little is known of how the desert and coastal populations are related or how they differ ecologically, but they certainly occupy very different environments. Whereas the desert birds can be seen gathering locally in high densities day or night, the coastal birds are among the more cryptic nesting species of southern California.
The conservation status of the Lesser Nighthawk near the coast is uncertain. Found from the Mexican border north into the San Joaquin Valley, this bird is now scarce in much of its range. In coastal San Diego County, it appears to be restricted to mesas and gentle hills at low elevations. The nighthawk may never have occurred in high density within this range but probably maintained its breeding population across the extensive mesas that are not largely occupied by human development.
The nighthawk ranges far on its nightly forays for food and social interaction, and because of its aerial foraging mode, likely does so independent of habitat. Its choice of nesting habitat, however, is much more specific. This bird requires an undisturbed, open, and relatively level place on which to lay its two speckled pale slate-colored eggs that resemble polished stones. Absolutely no nesting material is used; the eggs are usually laid among small pebbles that may or may not match the color of the eggs.
In comparison to our neighboring counties to the north, San Diego County still has many acres of undeveloped coastal terrace. But most of this is not suitable for nesting nighthawks because the proper combination of conditions is not met. Dense brush precludes nesting because open ground with cobbly or fine-grained soil is not available. Therefore, nesting nighthawks are most often found in the naturally more open coastal sage scrub. Chaparral is generally too dense, although local soil conditions may support a sparse "dwarf" stand that is suitable. In many areas of disturbed scrub the woody cover is open enough, but such disturbance is usually accompanied by a rank growth of nonnative weeds, also unsuitable for nighthawks. A further restriction in nighthawk distribution is the scarcity of suitable cover in large areas of nearly level terrain. Much of the terrain remaining free of development and agriculture is too steep for the placement of the nighthawk's unsheltered eggs.
The final crucial element for nesting nighthawks is seclusion from human disturbance, which requires large undeveloped tracts. Nighthawk nests are quite vulnerable and the birds are sensitive to disturbance, readily abandoning their reproductive investments when molested. Many of our undeveloped coastal lowlands are not sufficiently buffered from even the most benign recreational traffic of people and domestic animals to be safe havens for nesting nighthawks. Thus the species is now relegated to a few remaining mesas, flat ridge tops, dry washes, and alkali basins.
When traversing atlas blocks, look for relatively flat terrain with undisturbed yet exposed soil. Adult nighthawks flush from the ground when intruders approach within a few yards of the nest and perform a low circling flight with accentuated wingbeats. The may utter a soft varying trill or hollow dovelike notes or a short nasal call. It is best to back carefully and quickly away from such displays, watching each footstep to avoid eggs, and moving through relatively dense vegetation. If you are fortunate enough to see at close range the point from which a bird flushes, a very quick inspection (preferably with binoculars) may reveal the eggs. However, not the sex of the bird flushed; males, which have the bold white wing patches and tail bars, do not incubate. The males are more likely to put on an aerial display and are probably the only ones to give the hollow trill. Females have duller wing patches, no white tail bars, and are more likely to drop quietly out of sight or utter a nasal chatter. Remember, prolonged human activity near the nest may cause abandonment.
If you visit your atlas block before late April, the Lesser Nighthawk may not yet have arrived from its wintering grounds. Nighthawks nest later than many lowland species, mostly in May or June. The young, however, develop rapidly and may be out of the "nest" in a week, so a visit later in the spring may not reveal the actual nest site. The juveniles are weak fliers, fluttering only a few yards to drop into another small opening among the shrubs. They are very drab, lacking any white in the wings or tail. Don't pursue the young, as they may be stressed by activity in hot weather. The adults are usually close by and may also flush excitedly if their young are disturbed.
These behaviors may be observed during daylight, but a dawn visit to a known nesting area may reward the observer with high aerial calls and displays. Conversely, observation of such behavior in an unexplored area may reveal the nearby nesting of this mysterious species. A better understanding of the Lesser Nighthawk will probably prove to be one of the more important results of the San Diego County Bird Atlas.
John Lovio, from the spring 1998 issue of WRENDERINGS, sketch by Brad Holderman