Two With Spots

Spotted Sandpiper (Actitis macularius)

It’s been a while since I’ve seen a Spotted Sandpiper (“Immaculate,” Sep 28 2021) and even longer since I’ve seen one on the west side of the park, facing the Golden Gate Bridge. But this morning I saw not only one but two. The last few seconds of the video above show a second bird. To human eyes they looked identical but they were a good 50 yards apart so I’m confident they were different individuals. If they’d been closer together I wouldn’t be so sure; both birds showed great talent at just disappearing into the rocks, leaving my camera to pull back and scan left and right without seeing them again. They showed great skill at navigating on slippery surfaces at the turbulent edge, where any wave could wash them away. They displayed great timing. Even if a wave overtook them, it would not be a disaster, as they can swim and even dive if need be.

These birds both showed well-developed spots, indicating they were in or near their breeding mode. When not breeding they are spotless. Males and females have practically identical plumage, with females being a good bit (20-25%) bigger than males, but you’d have to see the sexes together to tell the difference. Females may carry spots farther down their bellies than males; if that’s so, given that these two have spots as far back as they can go, these two may be females. Unlike many other birds — for example, Red-winged Blackbirds — females migrate earlier than males. Females establish nesting territories and then hunt for males for mating. In some settings, the female mates with only one male. In many others, she may couple with two, three, or four males, and lay a clutch of eggs with each one of them. The females aggressively defend their territories, and fights between females competing for a male may result in injuries. Once the eggs are laid, it’s the male’s job to sit on them until they hatch, regardless whether he happens to be the father of that clutch. Sometimes the clutch on which he’s sitting has even been laid by a different female. It’s all very novel and confusing for the human observers, but the birds seem to work it out ok. Males and females have gender-typical levels of testosterone, with males having much higher levels than females. This leads scientists to conclude that testosterone levels are not the cause of the birds’ role reversal in breeding and brooding. But males of this species have significantly higher levels of prolactin during the breeding season. Prolactin is a hormone that promotes parental care, and prolactin levels are linked in a positive feedback loop with the male’s time spent incubating.

Spotted Sandpipers are known to breed in San Francisco Bay, but they strongly prefer sheltered territories free of mammalian predators. Such habitat would exist in Chavez Park if the Off-Leash Area were properly fenced and gated and the Berkeley leash law enforced, but given the current Wild West conditions, safe breeding territory for these sandpipers and other ground-nesting species does not exist in the park.

Spotted Sandpiper (Actitis macularius)

More about them: Audubon Wikipedia Cornell Previously on chavezpark.org

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One thought on “Two With Spots

  • April 9, 2022 at 3:29 am
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    And this bird wasn’t just out for a stroll…. Watch it sneak up and catch and swallow a prey at 26 seconds. (Put the video into .25X playback speed, or stop-motion for frame-by-frame stepping, to better catch the brief moment.)

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