Bay Area Birds - Sample Text
SHEARWATERS and PETRELS (Procellariidae)
[Note: Over two dozen species of albatrosses, shearwaters, petrels, and storm-petrels have been found along the central California coast and they range from extraordinarily rare to abundant. Finding these birds can be challenging and exciting, and often requires taking an offshore boat trip. These birds of the open ocean have lives that are mostly or entirely peripheral to the Bay Area, plus their numbers vary dramatically from year to year based on ocean temperatures and currents, so only twelve species that are common, expected every year, or uniquely characteristic of the California Current are included below and in Appendix 1.]
Sooty Shearwater Puffinus griseus
Life History Sooty Shearwaters are one of the ultimate seabirds, utilizing ocean resources so efficiently they are among the planet’s most abundant birds (an estimated 20 million!). The population in the Pacific Ocean breeds on islands around New Zealand from October to March, taking advantage of abundant food resources during the Southern Hemisphere summer. Then in March they begin what is perhaps the most stunning migration undertaken by any animal, traveling 34,000–46,000 miles in a giant figure-8 loop around the Pacific Ocean that brings part of the population to the California coast in May–July just as food resources peak in the California Current. They eat large numbers of fish and squid, collecting them from the ocean surface or by diving 45–220 ft underwater. While in the Bay Area they fatten up and complete their premigratory molts by feasting on dense schools of post-spawning anchovies that rise to the surface during the day in the Gulf of the Farallones and in Monterey Bay. Sooty Shearwaters usually do not find their own food, but converge after murres or gulls find a rich food source first.
Sadly, their numbers in the California Current have declined 90 percent since the early 1990s. Prior to this decline, an estimated 4 million Sooty Shearwaters occurred each year along the California coast with flocks of 1000 to 27,000 birds once common, and one stunning flock of 631,000 birds found on Monterey Bay in late June, 1981. It is not clear if there has been a real drop in numbers or if they are using different parts of the Pacific Ocean but these wide-ranging birds provide a snapshot of global ecological health so scientists are concerned by this apparent trend.
In a quirky aside, their massive numbers at Monterey Bay might have been the inspiration for Hitchcock’s movie The Birds, which was influenced by a real-life event in 1961 when thousands of shearwaters poisoned by toxic algae crash-landed all over Santa Cruz.
Note: Due to their similar appearance, little is known about the seasonal abundance and status of Short-tailed Shearwaters (P. tenuirostris) that mingle in much smaller numbers among vast flocks of Sooty Shearwaters. With an improved understanding of how to identify them, bird-watchers now suspect that Short-tailed Shearwaters are rare along the coast (occasionally common at Monterey Bay) from November–March, during a time when Sooty numbers are at their lowest.
Range Sooty Shearwaters are common to abundant along the central California coast from late March to early November, though they can be found year round. Peak numbers occur May–July, and they show a second peak in late August–early September as the bulk of the population begins an epic journey towards New Zealand (traveling 300–680 miles a day). Most stay well offshore, but at times phenomenal numbers can be seen along the shore or flying by coastal headlands. Sightings of Sooty Shearwaters drop off dramatically by mid- to late September.
Brandt’s Cormorant Phalacrocorax penicillatus
Life History Cormorants are gangly, short-winged seabirds that look bedraggled and out of proportion on land, but in the water they are incredible predators that can chase down fast-moving fish at surprising depths (over 200 ft deep). With little body fat, dense bones, and no waterproofing on their feathers they have eliminated the buoyancy that compromises the diving ability of many other birds, but after a feeding session they retreat to perches out of water to spread their wings and dry their feathers.
Brandt’s are almost entirely restricted to the California Current, and a very large percentage of their global population (which numbers around 75,000 pairs) breeds on the central California coast where strong upwelling waters create one of the world’s most highly productive marine environments. However, the fickle nature of the California Current means local marine food chains go through a boom and bust cycle, with significant impacts on populations of Brandt’s Cormorants and other seabirds breeding in the Bay Area.
In a good year with cold, strongly upwelling water, Brandt’s Cormorants gather on the ocean surface in large dynamic flocks that roam in search of abundant food items like juvenile rockfish (around the Farallon Islands) or anchovies (in San Francisco Bay). Actively foraging cormorants dive and splash in a rolling frenzy, with birds at the back of the flock continuously flying to the front of the pack and immediately diving in pursuit of their fleeing prey. They consume 10–27 percent of their body weight in fish each day, so in a year with weak upwelling and diminished productivity they break into smaller groups and switch to a diet of bottom-dwelling fish and smaller numbers of whatever fish they can find.
Because they are so dependent on the degree of upwelling and the resulting food supply, the numbers of breeding pairs can vary dramatically. On the Farallon Islands, the numbers of nesting pairs oscillated from 14,000 in 1979, to 0 in 1983, to 10,000 in 2002, and just under 1300 in 2009. A small colony on Alcatraz Island had 460 pairs in 2002, 1700 pairs in 2007, 0 pairs in 2009, and 200 pairs in 2010.
After dispersing widely along the entire Pacific coast in the winter, Brandt’s Cormorants begin returning to their nesting areas around mid-March. They are susceptible to predators (adults do not defend their nests and chicks) and vulnerable to disturbance from people, boats, and low-flying planes, so they nest on inaccessible islands or areas protected by rugged cliffs.
Few people have a chance to witness their breeding behavior but colonies are generally located on the flat tops or gentle slopes of islands, and older males return first so they can claim the best sites in the center of the colony. Males pile up as many grasses and bits native vegetation or seaweed as they can find, then display to passing females by crouching down with tails spread and heads thrown back to show off their flashy blue throats and elegant facial plumes. The scarcity of green plants on rocky islands means nesting materials are at a premium so pairs constantly steal from each other and can only build up a nest mound by having the female stand guard and construct the nest while the male goes on expeditions to find more nesting material. Parties of males will sometimes launch raids to steal nesting materials from Western Gulls, even dismantling nests from under sitting gulls as they loudly protest.
Brandt’s Cormorants do not start breeding until they are at least two years old, with the majority of birds breeding by age four. Younger birds are also the first to forgo their breeding efforts in low food years. Over the course of their lifetimes (no more than 21 years) adults typically breed 2–3 times and successfully raise 2–4 chicks, though the record is a male that bred eight years and reared 20 chicks.
One to four eggs are typically laid from late April to early June, but the date varies each year depending on ocean conditions and food supplies. Some birds that initiate courtship and build nests do not lay eggs, especially in years with low prey availability. Incubation lasts about 30 days, with pairs taking turns incubating their eggs by standing on them and warming the eggs with their webbed feet. Chicks hatch asynchronously, which is an effective strategy when food supplies are unpredictable because the oldest chick gets fed first, and then if there is enough food the next oldest chick gets fed, and so on, with the youngest chicks dying of starvation if there is not enough to go around. Chicks are helpless for several weeks and will be harassed by neighboring cormorants or eaten by gulls if left unattended, but they are soon strong enough to shove their heads down the throats of their parents and pull out partially digested fish for a tasty meal. Young chicks gather together in increasingly larger groups (crèches) until they leave the colony in late summer and early fall.
Range Brandt’s Cormorants are widespread on the California coast, but their greatest numbers occur in the Bay Area. The largest breeding colony in the world is located on the Farallon Islands, but there are many other smaller colonies on suitable rocky islands and rugged cliffs along the coast. Breeding adults forage near their colonies and are found in a relatively narrow zone along the coast, seldom occurring farther than six miles offshore (except at the Farallon Islands). They are rare in estuaries and bays (though they enter Tomales Bay when herring are spawning), but they are common inside the mouth of San Francisco Bay and began breeding on Alcatraz Island in 1991.
After the breeding season about 50 percent of the birds, mostly juveniles plus some adults, immediately disperse northward along the coast as far north as British Columbia, where they either remain for an extended period of time or begin heading back south in the fall. At the same time, smaller numbers disperse southward; with the overall effect that their total population goes from being highly clumped in central California during the breeding season to being widely dispersed along the entire Pacific Coast during the nonbreeding season. In years when food supplies are lowest, many dead juvenile birds wash up on beaches in September–October. The lowest numbers in the Bay Area occur during the winter, then numbers surge in March–May as they return to their nesting colonies.
Double-crested Cormorant Phalacrocorax auritus
Life History Double-crested Cormorants were common in the Bay Area until the 1940s when their populations suffered a major decline that lasted until the 1970s, from which they are only recently beginning to recover. This increase in numbers has been mirrored in the establishment of new and growing nesting colonies around San Francisco Bay—including colonies discovered on the Richmond-San Rafael and Bay Bridges in 1984, and a colony on the Dumbarton Bridge in 1988.
Unlike other cormorants, Double-crested Cormorants avoid the uncertain productivity of the California Current by specializing on a relatively limited diet of fish they capture in large bays and shallow coastal waters, as well as on large rivers and freshwater lakes. Birds that breed on the Farallon Islands, for instance, make 45-mile roundtrip flights to catch dependable surfperch along the coast rather than forage around the islands for rockfish (an erratic food supply) with Brandt’s Cormorants. Double-crested Cormorants typically dive in shallow waters (less than 25 ft deep) over flat bottoms, and where food is abundant they often feed in large “leapfrogging” flocks, as may be observed when they gather to feast on herring in the winter. Their diets and primary foraging habitats overlap very little with other cormorants.
Many aspects of their breeding biology match those of Brandt’s Cormorants, but where the two species nest together Double-cresteds are restricted to steeper slopes. Double-crested Cormorants prefer to nest on the ground but use a wide variety of sites including old wharves, pilings, trees (especially dead trees surrounded by water), power poles, and bridges.
The oldest males begin returning to their colonies in mid-March, building nests of seaweed and displaying in the fashion of Brandt’s Cormorants, but differing in adding sticks, feathers, and bones to their nests. They are also less sensitive to disturbance than other cormorants, which partly accounts for their willingness to nest on bridges. The 3–4 eggs hatch in 30 days, and chicks join mobile crèches (nurseries for young birds) at 3–4 weeks of age. In trees or on bridges, where chicks cannot move around, they remain on their nests until they can fly at 6–7 weeks of age. Chicks fledge by late July, but are still fed by their parents until August or September.
Range Although Double-crested Cormorants are widespread and familiar cormorants in much of North America, their distribution in California is limited and they are the scarcest of our three cormorant species. Except for their colony on the Farallon Islands (just under 200 pairs in 2011), they are surprisingly scarce breeders along the outer coast, with only a few small colonies in the area covered by this book. They are similarly scarce at inland locations, where they may nest with herons and egrets in trees, but they are fairly numerous around San Francisco Bay (over 1100 pairs in 2011) making this one of their primary nesting areas on the California coast. In addition to this nesting population, numerous nonbreeding birds hang out all summer-long on estuaries, bays, lagoons, large rivers, and reservoirs.
Double-crested Cormorants become more noticeable in August as postbreeding adults and juveniles disperse from their local nesting sites. Although juveniles, and some adults, head north up the coast, and larger numbers leave for southern California, there is still a significant increase in overall numbers from November to March as cormorants from interior areas move to the coast for the winter. While wintering Brandt’s and Pelagic Cormorants are almost completely restricted to the outer coast, Double-crested Cormorants favor the sheltered waters of large bays and estuaries. The highest Christmas Bird Count numbers in the Bay Area come from San Francisco, southern Marin County, and Oakland: all clustered around the central portions and mouth of San Francisco Bay.
Pelagic Cormorant Phalacrocorax pelagicus
Life History These charming smallish cormorants, showing red faces and startling white flank feathers in the breeding season, live in a very narrow coastal band around the perimeter of the subarctic Pacific Ocean. They nest exclusively on sheer cliffs directly over and facing the ocean, where they take advantage of their size to nest on narrow ledges few other birds use. They are not particularly social or colonial but end up nesting in loose groups on cliffs with multiple ledges. Although they are restricted to coastal cliffs where they nest in small numbers at each location, Pelagic Cormorants are still our most widespread local cormorant because they use almost every cliff face and rocky island along the entire coast.
From these precarious colonies Pelagics undertake short foraging expeditions into nearby waters over rocky reefs, where they dive up to 400 ft in search of various fish. Along the coast they forage for fish hiding among underwater rocks, while around the Farallon Islands they eat more rockfish in cold-water years and more sculpins in warm-water years. It is possible they prefer rockfish when these fish are abundant because large chaotic flocks of seabirds gather to eat rockfish when they are available, thus making it more efficient to simply look for clusters of feeding seabirds than to find the prey yourself. Overall, their diet is fairly restricted and does not overlap with other cormorants but closely resembles that of Pigeon Guillemots.
Along the California coast equal numbers of Pelagic Cormorants nest on offshore islands and on mainland cliffs, but their specific nest locations change frequently, partly because this species is more sensitive to oscillations in the ocean environment than any California seabird. Counts of nesting pairs on the Farallon Islands, for instance, change dramatically from year to year: some years they do not breed at all, while other years they abandon their nests, eggs, or chicks at a moment’s notice if food supplies begin to dwindle. Even in a good year, fewer than half of all eggs may hatch. Fortunately, Pelagic Cormorant populations apparently recover quickly after a poor year.
At the Farallon Islands, anywhere from 0–100 percent of the breeding population sticks around through the winter, and some years pairs reoccupy their nest sites in December or January, while other years they wait until April–May. Like other cormorants, Pelagics construct nests from bits of grasses, native vegetation, and seaweeds, but they are unique in cementing their nests solidly in place with feces to keep them from slipping off narrow ledges. Most pairs begin tending eggs and chicks in May or June, but eggs have been observed as late as early August. The 3–4 eggs are incubated for 30 days, with parents taking turns holding the eggs on top of their feet and pressed against their breast feathers. Chicks grow so fast they reach adult size in about eight weeks, and due to their perilous nest locations chicks do not gather into crèches as other cormorants do. Chicks fledge sometime between late July and early October.
Range Although Pelagic Cormorant nest along the entire California coast, a significant percentage of the total California population nests on the Farallon Islands (100 pairs in 2011) and along the coast immediately north of San Francisco Bay. Smaller numbers also nest along the coast between San Francisco and Santa Cruz. They began nesting at Alcatraz Island in 1986; a pair nested at Yerba Buena Island in 1990; a pair nested on the Berkeley Marina in 2007; and pairs have nested sporadically at Pt. San Pablo.
Observations suggest that most, if not all, of these birds are year-round residents, remaining along the coast or shuttling back and forth to the Farallon Islands. In addition to the coast they also enter the mouths of large bays, but seldom enter estuaries and lagoons except occasionally in late summer as they first disperse from their breeding sites. When herring spawn in Tomales Bay, Pelagic Cormorants show up in small numbers but they are by far the scarcest cormorants. Similar numbers of wintering birds occur at the entrance and in the central portions of San Francisco Bay. Christmas Bird Counts along the coast each average about 60-150 birds, suggesting the total population must be fairly small.
American White Pelican Pelecanus erythrorhynchos
Life History These huge white birds are an ungainly mix of elegance and awkwardness—simply folding up wings that span nine ft across, or landing and taking off from water seems to cause them consternation. Once airborne, however, they are awe-inspiring as they circle high overhead in precise formations. They have an amazing ability to glide effortlessly on rising air currents and will travel great distances in search of food—on their breeding grounds they regularly fly 200–600 miles to gather fish for their chicks. In the Bay Area they appear to commute almost daily, even multiple times a day, among far-flung feeding sites, with the result that pelicans might show up for a few hours or days then disappear just as quickly.
Unlike their sea-going cousins, white pelicans favor shallow wetlands while they are in the Bay Area. They appear in groups ranging from single birds to hundreds that forage in waters less than three ft deep and rich in fish. These large birds eat about three pounds of fish a day so they are active feeders, dipping their huge bills into the water like nets and scooping up small fish. If fish are scattered or occur in low numbers pelicans feed individually, but as soon as a pocket of food is detected pelicans briefly gather in groups that cooperate by lining up shoulder to shoulder to chase and trap fish inside a closing circle of pelicans. They also steal fish from diving birds like Double-crested Cormorants. When not feeding or flying between feeding sites, pelicans roost in large groups on sandspits in coastal estuaries, or on levees in managed wetlands.
Range American White Pelicans seem to use the Bay Area in complicated and not fully understood ways. In February–March, breeding adults leave for a handful of nesting colonies divided between northeastern California, Malheur National Wildlife Refuge in Oregon, Pyramid Lake in Nevada, and at the Great Salt Lake in Utah. Their return migration is not well described but some adults show up in the Bay Area in July and juvenile birds continue to show up through September. What complicates this picture is that white pelicans do not start breeding until they are three years old and fairly large numbers of nonbreeding birds spend the entire year in the Bay Area, even hanging out at some sites for months at a time. In other areas there are long unexplained absences and it is not known whether these “missing” birds move to the Central Valley, move to other Bay Area locations, or leave the area entirely. In drought years, many pelicans stick around rather than head to their breeding grounds.
While in the Bay Area they are particularly abundant around the North Bay and South Bay salt ponds, with smaller numbers commuting between a variety of coastal estuaries, sheltered bays, brackish wetlands, and large freshwater lakes and marshes. Because of their fickle movements it is hard to summarize their seasonal status and regional distribution, but their overall numbers increase from May through the summer and fall, and then several thousand spend the winter in the Bay Area. At the South Bay salt ponds they reach peak numbers from July–October, while at Point Reyes they reach peak numbers from October to January and at Monterey Bay from November to February, but it is unknown if these dates are linked in any way. By late winter their numbers diminish, but at variable rates in different years, and there might be a small peak in April–early May, which could represent migrants moving toward their breeding areas.
Brown Pelican Pelecanus occidentalis
Life History Despite their near-extinction from the United States in the late 1950s–early 1970s (due to DDT), Brown Pelicans have launched a stunning comeback and are once again a characteristic and ubiquitous coastal bird. During their summer–fall peak, well over 20,000 Brown Pelicans now roam the central California coast, where they congregate to feed in the highly productive upwelling waters of the California Current. However, like other coastal birds they are vulnerable to long-term oscillations in ocean temperatures and currents and their numbers can swing dramatically from year to year. For instance, on three consecutive years the Southern Marin Christmas Bird Count recorded 10; 2498; and 63 pelicans.
Unlike white pelicans, Brown Pelicans catch fish in spectacular dives that are launched from as high as 60 ft and end with a big splash as they plunge head-first into the water to scoop up fish up to three ft deep. If you watch closely you will notice that as they enter the water they roll to the left to protect their trachea and esophagus which are fixed to the right side of their necks. Extensive air sacs under their skin cushion the impact of their dives and help buoy them back to the surface. They mostly eat schooling fish such as anchovies and smelt, and on the open ocean they seek out highly productive zones where cold upwelling waters collide against warm-water currents. Heermann’s Gulls (and to a lesser degree Western Gulls) accompany Brown Pelicans and wait for fish scraps, while the activity of pelicans diving on schools of fish attracts seabirds from miles around.
Surprisingly, Brown Pelicans become waterlogged after an hour on the water so they frequently retreat to dry perches and these social birds use the same roosting areas year after year, often in huge numbers (thousands at a time are possible). These roosts are typically on isolated beaches, offshore rocks, or on pilings and wharves.
Range Brown Pelicans are late summer visitors that wander up the coast after breeding in the Gulf of California and southern California. In a successful year they begin leaving their Baja California colonies in June, and their southern California colonies in July, with many still heading north in August; but in an unsuccessful year many abandon their colonies months earlier and show up in the Bay Area in March–April. Although small numbers continue north to British Columbia, most stop on the stretch of coast between Pt. Lobos and Bodega Bay. Here their numbers continue to increase through the summer, reaching a peak in September–October. Most are found along the coast but they also enter coastal estuaries and bays, and they are fairly numerous inside the mouth and central portions of San Francisco Bay (but are scarce past San Pablo Bay or in the South Bay). Thousands have also been observed around the Farallon Islands, including a one-day count of 5700 in early September, indicating that many use the islands as a base for foraging in the extremely productive waters of the Gulf of the Farallones. Because they begin nesting and laying eggs in November–December, most leave the Bay Area abruptly in November. Historically, winter numbers have been very low from December to March but in recent years many more have stayed behind and at least four local Christmas Bird Counts now record well over a thousand birds some years.
HERONS and EGRETS (Ardeidae)
American Bittern Botaurus lentiginosus
Life History Populations of these solitary, cryptically camouflaged wading birds have been dramatically reduced throughout their range due to the widespread destruction of freshwater marshes with extensive stands of tall emergent vegetation. Bitterns were probably never common in the Bay Area and are now rare residents. Finding a bittern is a matter of luck or hard work and very little is known about their life history, much less their status and distribution. The few nests known from the Bay Area have been mostly found by accident, but adults are occasionally observed feeding young birds in mid-June.
Hiding amid dense marsh vegetation and rarely coming into the open, bitterns are best looked for at dawn and dusk when they begin actively hunting for insects, frogs, fish, and other small vertebrates. In the breeding season you may hear their eerie thumping pump-er-lunk calls resonating across a marsh, or you may see them flush up in brief flights as they move around trying to find mates or chase away intruders. Females build nests amid dense, emergent vegetation and tend the eggs and chicks by themselves. Incubation lasts about a month, and chicks remain in the nest for 1–2 weeks then linger nearby for another 2–4 weeks.
Range Bitterns reside in freshwater marshes, or around the margins of lakes with extensive stands of tall cattails and bulrushes; to a lesser degree they use brackish marshes if no other habitat is available. The Bay Area probably has a small resident population, though actual numbers are unknown due to their highly secretive nature. There are very few nesting records but American Bitterns likely breed in any part of the Bay Area with suitable habitat. Their numbers, or at least their visibility, seem to increase from September–April. A large percentage of all bitterns reported in the Bay Area are found at a few traditional spots, where a handful of individuals probably account for most sightings. These locations include Abbott’s Lagoon at Point Reyes, Spring Lake and Shollenberger Park in Sonoma County, and North Lake in Golden Gate Park.
Great Blue Heron Ardea herodias
Life History These common and widespread wading birds show up anywhere in the Bay Area where there is water. Their preferred foraging habitats are shallow waters along the edges of ponds, lakes, and rivers, but they are readily seen in places as diverse as schoolyards, agricultural fields, neighborhood parks, and grassy highway shoulders. On occasion they may be observed standing on top of high trees or rock outcrops, and along the coast they stand on masses of floating kelp.
Great Blue Herons are correspondingly universal in their food choices and eat just about any animal they can catch and swallow: everything from fish (their primary food) and frogs when hunting in water, to gophers and snakes when foraging in fields. Hunting herons walk slowly or stand motionlessly, then make captures with lightning fast strikes. Other hunting strategies include hovering, diving, swimming, flicking their wings open to startle prey, and running. They are mostly solitary and exhibit antagonistic behaviors towards other herons, signaled by erected feathers and partially spread wings, but they are gregarious while nesting and are sometimes plentiful in areas of abundant food in the wintertime.
Great Blue Herons nest in colonies that range from single pairs to dozens of pairs, often nesting side by side with egrets and night-herons. Many of the 60+ colonies in the Bay Area are small and short-lived, with nesting herons moving around and utilizing the landscape fluidly. Nearly all nests are located in tall trees such as eucalyptus, redwoods, Douglas firs, and gray pines; usually on hillsides with commanding views, or on floodplains near water. In the Bay Area, they begin returning to their colonies (heronries) surprisingly early, with males gathering in the vicinity of previously established colonies by late December. From early January into March pairs engage in elaborate courtship rituals—including lots of neck stretching, feather ruffling, and stick shaking—as males bring sticks to their mates, who either toss them aside or weave them into messy platforms that after several years of use can grow to be bulky structures measuring nearly four ft across and three ft deep.
Chick-rearing is an extended effort by both parents, with the first eggs being laid from late February to early March (some clutches are laid in early summer). Both adults incubate their 3–4 eggs for about 28 days with eggs hatching sequentially over several days in the order they were laid. This asynchronous hatching leads to competition among the nestlings, with the oldest young having a significant advantage in times of food scarcity. Chicks clamber around their nests on progressively more adventurous forays for several weeks then fledge when they are 2–3 months old.
Range Great Blue Herons appear to be common local residents that do not migrate, but there is considerable movement through the seasons. During the nonbreeding season they show up around the margins of almost any type of water body, including coastal beaches, estuaries, tidal marshes, lakes, rivers, and wetlands. They use the same habitats during the breeding season but are more locally concentrated near active colonies. There are about 500-600 nesting pairs in the Bay Area, but their overall numbers appear to decline during the early part of the nesting season because one parent always stays at the nest until the young are 3-4 weeks of age. By May or June, when chicks are old enough to be left alone, the apparent number of herons jumps as both parents begin foraging again. There is another increase when adults and fledglings begin leaving heronries in June. Their postbreeding dispersal is reflected by their appearance at nonbreeding locations like Abbott’s Lagoon and the Farallon Islands from August to mid-October. Because ponds and wetlands shrink in late summer and fall, foraging herons may become concentrated until winter rains rejuvenate dried-up feeding areas.
Great Egret Ardea alba
Life History Thanks to the tireless efforts of the staff and docents at Audubon Canyon Ranch, thousands of schoolchildren each year have a chance to witness nesting Great Egrets first hand, making this majestic bird one of the Bay Area’s totem animals. In fact, everyone in the Bay Area is lucky this large nesting colony in West Marin was saved from development because both the colony and the adjacent foraging grounds on Bolinas Lagoon are fantastic places to watch these birds close up. Excessive hunting for the millinery trade (womens’ hats) in the late 1800s led to the near-disappearance of these birds, but they slowly rebounded in the 1900s and there are now more than 25 nesting colonies with about 1300 nesting pairs in the Bay Area.
These slightly smaller and slimmer versions of Great Blue Herons share many similar life history traits, and the two species are often seen feeding and nesting together. Great Egrets also frequent shallow waters around estuaries and wetlands, and like Great Blue Herons they show up in fields and grasslands in search of just about anything they can catch and swallow. Their premier feeding and nesting area in the Bay Area is Suisun Bay where freshwater flows of the Sacramento and San Joaquin Rivers mix with incoming saltwater currents to create a zone of extremely abundant plankton, and the highest numbers of larval and juvenile fish in the San Francisco Bay estuary.
While Great Blue Herons utilize a wide variety of habitats and nest in many small, dispersed colonies, egrets are more narrowly distributed and nest in a handful of larger, more persistent colonies (though some colonies are also small and short-lived). The colony at Audubon Canyon Ranch, for example, has at times exceeded 100 nests, and a colony at Elkhorn Slough has had more than 60 nests. Great Egrets almost always nest alongside other wading birds, including a colony at the Napa State Hospital where they nested with both Snowy Egrets and Black-crowned Night-Herons. Although Great Blue Herons readily nest in forested areas, Great Egrets prefer tall trees in more open areas near bayshores, such as at Suisun Marsh where they nest in isolated eucalyptus groves in the midst of open wetlands or near San Rafael where they nest on a tiny island in the open bay.
During the winter, Great Egrets are widespread and thinly dispersed over countless tidal mudflats, estuaries, marshes, and freshwater ponds and lakes, but by early March breeding adults move back to their nesting colonies. Males pick potential nest sites and begin displaying for mates by stretching their necks, bowing, erecting elegant white plumes, and snapping their bills. Many details of their nesting biology match those of Great Blue Herons (see above), but they nest a bit later. Egg-laying, for instance, peaks in early April rather than early March. Chicks are physically able to fly at 7 weeks of age but generally remain at or near the nest until they are 10–12 weeks old. During this time, they begin making short hesitant flights between branches, leading to brief exploratory excursions until they are ready to leave the nest. Although immature birds visit nearby foraging areas in the day they still fly back to the nest each night for several more weeks.
Range Great Egrets are fairly common to common residents throughout the Bay Area, but they may be slightly less abundant along the outer coast (Audubon Canyon Ranch and Bolinas Lagoon being a notable exception). They utilize freshwater wetlands, estuaries, and rivers everywhere in the Bay Area so it is surprising there are few nesting colonies here. Except for the heavily used area around Suisun Bay, there are generally no more than 2–3 large colonies in any single Bay Area county. Overall numbers in the Bay Area appear mostly stable, and Christmas Bird Count numbers are fairly consistent year after year.
Snowy Egret Egretta thula
Life History Compared to their two larger cousins, nesting Snowy Egrets are slightly less common in the Bay Area and establish colonies in fewer locations (only 12 colonies and 600 pairs in one recent survey), where nest in trees, among shrubs, or in stands of dense bulrushes and cattails. They favor wild places but will also nest in residential areas along with Black-crowned Night-Herons, Great Egrets, and Great Blue Herons. Snowy Egret nesting numbers show wide annual fluctuations, not only in the Bay Area but also nationwide. For instance, one large colony in the Bay Area went from a high of 500 nests in 1982 down to 220 nests in 1992, and then the entire colony collapsed in 1994 because a juvenile Red-tailed Hawk harassed them (there were only 8 nests that year!).
These small wading birds are active, almost frantic, hunters that dart back and forth in the shallow waters of wetlands and tidal marshes. More than other wading birds, they use their entire body as they forage, flicking their wings open and vibrating their yellow feet in murky water to scare up hiding fish and crustaceans. Much of their diet (perhaps 75 percent) consists of fish but they eat any type of small organism that is locally abundant, with most prey items being too small to be identified by a human observer. They frequently hunt together in large numbers or mingle with other wading birds (strategies that increase their feeding efficiency), but will also feed alone. High counts in the Bay Area include groups of 300–400 Snowy Egrets foraging together in the South Bay in late July–early August. These groups gather around dense patches of food and usually include juvenile birds learning to find and capture prey.
Nesting Snowy Egrets are concentrated at a few large to very large colonies in the Bay Area. Their limiting requirement seems to be colony security rather suitable nesting substrates, which may explain why colonies are readily abandoned in the face of threats that range from predation by nonnative red foxes, to human disturbance, to lowered water levels that connect islands to the shore. On the plus side, they have shown a willingness to nest in restored wetlands after bulrushes were planted. Their nesting season begins later than other local wading birds, and is signaled when males display by stretching their bills toward the sky while pumping their bodies up and down and making loud wah-wah-wah calls. Courtship may begin in March, and most pairs are incubating their 3–5 eggs and raising chicks during April–June. Chicks start scrambling out of the nest at approximately 10 days of age then spend increasing amounts of time out of the nest, but fledglings continue hanging out around the colony for another month or more even after they can fly.
Range In the early 1900s, Snowy Egrets were thought to be extinct in California but they have since recovered to what might be their current carrying capacity in the Bay Area. They are now common year-round residents in the Bay Area and through the Delta into low-lying areas of the Central Valley. Although some have been breeding around San Francisco Bay for at least half a century, they only started nesting in Sonoma County in 1991, in Napa County in 1992, and in Monterey County in 1997; though these records may partly reflect an increased monitoring effort throughout the region. Before they began nesting in Monterey County they were fairly common visitors from July to March, which seems to be the timing of their nonbreeding season.
Large nesting colonies include West Marin Island near San Rafael, Alcatraz Island, and Lake Merritt in Oakland. From these colonies Snowy Egrets fan out onto nearby tidal mudflats and brackish marshes to feed. For example, Snowy Egrets from West Marin Island seem to cross the Bay and feed along the Berkeley bayfront. After the breeding season, adults and juveniles disperse widely and can be found on many types of shallow freshwater, saltwater, or brackish ponds, marshes, lakes, and estuaries; their numbers are generally higher at inland locations than along the outer coast. Recoveries of banded juveniles hint that at least some migrate south to Mexico in the winter, while many adults may be year-round residents.
Green Heron Butorides virescens
Life History Dark greenish and well hidden amid the shadows of dense streamside thickets, Green Herons might be totally overlooked if they did not fly off with squawking skow calls when startled. In flight they may be mistaken for crows without tails, because most people do not expect to see otherwise secretive herons in the open. They are generally considered uncommon in the Bay Area but breeding surveys have found Green Heron territories stacked one after another along the lengths of slow-moving streams or around the perimeters of suitable wetland habitats.
Unlike other wading birds, these small herons are loners (at least in the Bay Area). When foraging they may stand motionless for long periods of time, waiting for approaching fish or other small animals. Green Herons are known for their strategy of “baiting” curious fish by dropping bits of potential food on the water surface then snatching up any fish that come near; they may also actively hunt by swimming, diving from above, or foot-stirring like Snowy Egrets.
Starting in late March or early April, males advertise their presence with “songs” that are little more than low-pitched ow-ch or skow calls. Herons that have migrated may already be paired up when they arrive because they begin nesting immediately. Pairs make flattish stick nests that range from astonishingly flimsy to solid and bulky, and they often use old nests as foundations for new nests. Nests may be built on the ground, but many are placed in trees (such as willows) standing over water. At times they nest in trees in suburban neighborhoods or along city streets—including a nest in downtown Santa Rosa—so long as there is a pond or stream nearby.
Pairs cooperate in all aspect of nesting and raising chicks. The 3–5 eggs are laid anytime from early April to late June and take about 20 days to hatch. Parents begin leaving their chicks unattended when they are 10 days old, and three-week old chicks can scramble out of a nest and cling to branches or even make their first flights. Chicks are pretty much independent at four weeks old.
Range During the breeding season, Green Herons are uncommon and found mostly along the heavily vegetated margins of lakes, ponds, marshes, and slow-moving streams, where they hide their nests amid dense foliage. There is a noticeable increase in numbers during fall migration from August to September, but then they are rare and highly localized from October to March. There is another noticeable peak in numbers as spring migrants begin to move through the area in April, particularly in late April or early May.
Black-crowned Night-Heron Nycticorax nycticorax
Life History Common all over the world and highly adaptable, these birds nest in a phenomenal range of conditions and eat almost anything they can catch and swallow—including unexpected food items like the eggs of marsh birds, carrion, plants, and garbage (at landfills). Night-herons roost at traditional sites during the day when they perch on tree branches or among the dense vegetation at the edges of marshes, lakes, and rivers. Their presence may only be revealed by their loud squawking calls, especially at dusk when they stir and depart their roosts for nighttime foraging sites. They feed as individuals but are gregarious on their roosts and at their nesting colonies where they may mingle with other nesting herons and egrets. Many colonies are located on islands in the Central Bay (about 50 percent of all nests in the Bay Area) or in large wetlands, but they are otherwise not picky about whether they nest on the ground, in stands of bulrushes, in dense shrubs, or in tall trees. In fact, more than any other local wading bird, they are not at all averse to nesting in the middle of small towns or in residential neighborhoods. Successful colonies may be used for decades, but they readily abandon even the largest and most well-established colonies. For instance, the Brooks Island colony just south of Richmond had 251 nests in 1995 and 0 nests in 1996; while the Bair Island colony near Redwood City had 684 nests in 1971 but was quickly abandoned when nonnative red foxes wandered into the area.
Nesting often begins in early April, even in early March, as males arrive at their colony sites and engage in feather ruffling, bowing, and stick-shaking to attract the attention of nearby females. The males’ elegant white plumes are essential to their future chances, and a pair bond dissolves quickly if a male’s plumes are lost or damaged at any point. With luck, a male may graduate from shaking sticks at a female to laying the foundation of a nest, which an interested female continues shaping as he brings more sticks to her. The pair cooperates in all aspects of their nesting effort, including incubating eggs for 25 days. Chicks start scrambling out of the nest at two weeks of age and need constant feeding until they are four weeks old.
Range Black-crowned Night-Herons are common permanent residents in the Bay Area with a relatively stable population (although the trend has been down in recent years). Their largest numbers are found in marshes and wetlands around the perimeter of San Francisco Bay, but there are smaller numbers scattered around large lakes, ponds, and estuaries elsewhere in the Bay Area. There is a small increase in numbers as visiting birds join the local population for the winter. Breeding birds are limited to a handful of both large and small colonies; in a 2005 survey there were at least 13 colonies in the Bay Area with around 800 active nests. Notable colonies include Lake Merritt, Napa State Hospital, Alcatraz Island, and West Marin Island. Colonies are frequently abandoned, but adults readily establish new colonies at other locations, so their population appears to be fluid and able to adapt to a changing environment.
GOLDEN-CROWNED KINGLET Regulus satrapa
LIFE HISTORY Despite being one of the most abundant birds in mid-elevation coniferous forests, Golden-crowned Kinglets are difficult to observe and their behavior during the breeding season remains virtually unstudied in California.
Equipped with unusually dense plumage, many of these kinglets remain year round on their breeding grounds even in frigid winter temperatures. During the winter, they occasionally mingle with chickadees and creepers but typically remain in small flocks of their own kind, often ranging into a wider range of habitats than they use during the breeding season. These agile birds have been called branch-tip specialists because they are so lightweight they can cling to tiny branch tips that would bend under the weight of heavier-bodied birds. Moving constantly, they scan branch tips and tree bark in search of adult insects, spiders, and mites, as well as their eggs, which are a plentiful food source in the winter.
Both sexes begin building deep, well-insulated cup nests in May, weaving needles and grasses together with spider webs and bits of moss and lichens for camouflage then adding a lining of feathers and hair. These nests are well hidden amid dense clusters of needles and rarely found. Males bring food to females as they incubate 5–10 eggs for 14–16 days. Both sexes then tend the young on the nest for 16–19 days, but while females almost immediately begin incubating another clutch of eggs, males care for the first batch of fledglings until they reach independence at 17 days of age.
RANGE Golden-crowned Kinglets are common residents in mid-elevation coniferous forests, but they will also range to both higher and lower elevations to nest in isolated groves of conifers away from the main belt of trees. A few wander to treeline in late summer, and may rarely nest as high as 10,000 ft. Some years, large numbers descend into the foothills, where they are possible in a wide variety of deciduous and coniferous forests. WEST SLOPE: Primarily breed in stands dominated by mature giant sequoia, red and white fir, and Douglas fir between 3000–8000 ft, where they are common to abundant from April–September. Golden-crowneds are surprisingly widespread, as shown by one Yosemite National Park study where they were detected in 22 different habitat types during the breeding season (compared to 5 habitat types for Ruby-crowneds). Also found in a wide range of forested habitats from the low foothills to 8000 ft in winter, but numbers are unpredictable at that season. EAST SLOPE: Locally uncommon resident in scattered pockets of firs and pines, but common at some locations (for instance, they are one of the 10 most common birds at Devils Postpile National Monument). Found the full length of the Sierra Nevada, though increasingly scarce and localized at the arid southern end of the range. Small numbers occasionally descend to valley bottoms and desert slopes in winter.
RUBY-CROWNED KINGLET Regulus calendula
LIFE HISTORY One of the joys of birding in the western foothills during winter is the ubiquitous presence of these abundant, noisily chattering kinglets. Their primary winter vocalizations are best compared to bursts of clacking typewriter keys though by the end of February males begin practicing songs that start as a series of high notes that build into a gallop of exuberant warbles. Grinnell and Storer, in their classic Animal Life of Yosemite, describe the song as see, see, see, oh, oh, oh, property, property, property. A month later, males depart to breed in montane coniferous forests, followed soon thereafter by females. Much of their breeding biology remains poorly known, in part because pairs build their well-insulated nests deep within dense needle clusters as high as 100 ft above the ground. Males attract females and challenge rivals by raising their otherwise hidden red crowns, sometimes stretching their bodies into exaggerated postures to highlight these colorful displays. By late May, females spend about 5 days constructing thick nests of mosses, lichens, and bits of plants, woven together with spider webs and thickly lined with feathers. Females incubate 7–8 white eggs for 12–14 days while males bring food. Clutches of 12 eggs are possible, the highest number of eggs relative to a bird’s size for any songbird in North America. Both parents tend the nestlings until they leave the nest around 16 days of age, and it is thought that families break up as soon as fledglings become independent. Ruby-crowned Kinglets seem to enjoy the company of other birds, especially in winter when they are nearly always found in the company of mixed-species flocks with warblers, nuthatches, chickadees, and other songbirds. They forage almost exclusively on the outermost foliage and often hover in mid-air to snatch small insects and spiders at the slender tips of branches.
RANGE Ruby-crowned Kinglets breed in montane conifer forests with a strong preference for lodgepole pine forests, especially near water or the margins of meadow. They sometimes appear in great numbers at low elevations during migration or winter. WEST SLOPE: An abundant migrant and winter resident in many types of forested and shrubby habitats below 4000 ft from late September to mid-April. During the summer, most apparently head north because they are uncommon breeders at higher elevations between May–July, when they are found mostly in lodgepole pine or mountain hemlock forests of the Subalpine Zone. Rarely breed as low as 4000 ft or up to 10,000 ft, and primarily found between 6000–8000 ft. EAST SLOPE: While huge numbers of migrants briefly show up in valleys and on foothill slopes in April, and a smaller number of migrants appear in late September to mid-October, numbers of wintering birds range from rare to fairly common. Though considered a common breeder in some locations, they are likely generally rare on their breeding grounds (6000–10,000 ft) from late April to late October.