Are bird populations that depend on the bay and surrounding lands stable?

Header photo courtesy of Marlin Harms.

Are bird populations that depend on the bay and surrounding lands stable?

Yes, the diversity of birds in the Morro Bay area appears stable. However, some birds face difficult conditions or are changing their behavior due to forces such as extreme weather events and habitat loss.

The habitats of the Morro Bay estuary and watershed support a wide diversity of bird species. Understanding the health of bird populations is a crucial tool for tracking environmental health. Across the country, a third of U.S. birds need conservation action for protection, which safeguards both habitats and the economy.

The North American Bird Conservation Initiative (NABCI) cites a loss of three billion North American birds in the past 50 years. While some groups of birds are faring better than others, loss of habitat and declining populations put all birds at risk. One of the best strategies for reversing this trend is researching species-specific declines to better understand what causes them and enact informed conservation measures. In the sections below, we highlight projects that are actively collecting valuable data on bird populations to aid in their management and recovery.

Snowy Plover Populations on the Morro Bay Sandspit

The western snowy plover is a small shorebird that nests directly on the sand. Plover nests are vulnerable to trampling, habitat loss, and being eaten by predators. In 1993, the federal government determined that this species required additional protection and management to improve its chance of survival.

California State Parks is responsible for managing plover habitat in the San Luis Obispo Coast District, which stretches from north of San Simeon to the southern end of the sandspit in Morro Bay. State Parks plover management consists of maintaining eight miles of fencing around nesting areas, monitoring predators, and increasing survey efforts during the breeding season (March to September).

The number of plover nests found on the sandspit during breeding season surveys has been declining since 2015. However, a recent uptick in 2024 resulted in the highest number of plover nests observed in the past five years (see graph above).

Despite the increase in total nests, the number of nests resulting in successfully hatched plovers has been relatively stagnant since 2019. On average, just under half of plover nests on the sandspit are successful (see graph above). Only 34% hatched in 2024, which follows two years of higher-than-average nest success. The main culprit for nest failure on the sandspit is predation by coyotes.

Even though the road to recovery for the western snowy plover has been long and challenging, the trend in our region is a gradual, positive trend in plover numbers, which would not be possible without the management actions and stewardship of State Parks and other partners.

Black Brant Migration Shifts

Black brant are a migratory species, stopping by Morro Bay in late fall to early spring, on their way to Mexico to escape the cold winter on the Alaskan tundra. They migrate along the Pacific Flyway, the north-south corridor for bird migration in the Americas that is over 4,000 miles long and up to 1,000 miles wide.

Eelgrass, a flowering marine plant that grows in the estuary, serves as an important food source for migrating black brant. In the past, the number of brant in the Morro Bay estuary has fluctuated along with changes in eelgrass acreage. During the most recent eelgrass decline period from 2007 through 2015, brant populations also decreased. Even though eelgrass has made a significant comeback in the past few years, the Morro Bay brant population has not rebounded to the same degree.

This decline in the Morro Bay brant population is due at least in part to a shift in temperature. As the Alaskan Peninsula continues to experience warmer winters, more brant are opting to skip the arduous 4,000-mile journey to warmer climes and instead remain in Alaska for the winter. This means fewer brant are stopping by Morro Bay to forage on eelgrass.

In the graph above, the falling green line represents the decreasing number of brant opting to winter in Mexico, while the rising red line shows the increasing number of brant remaining in Alaska for the winter. Winter 2023 marked the first year since data collection began that more brant remained in Alaska rather than migrating south to Mexico.

Fortunately for brant, the decline observed in our local population is not reflective of the population along the entirety of the Pacific Flyway. The Pacific Flyway population has remained relatively stable, meaning that the change in migration pattern has not yet impacted the brant population as a whole.

Tracking Our Shorebirds

Since 1988, Point Blue Conservation Science and the Morro Coast Audubon Society have conducted annual surveys to track overwintering shorebird populations within the estuary and along nearby beaches. During the survey, volunteers venture out into the estuary by foot and by kayak to pre-defined survey areas. They then identify and count all shorebirds that use the survey area, record the current weather conditions, and make note of important habitat characteristics. Their combined efforts result in a reasonably complete census of overwintering shorebird populations.

The Morro Bay estuary is split into twelve zones for the fall shorebird surveys. During the latest survey conducted in November 2024, Marbled Godwits and Willets dominated the Front Bay (blue), Western Sandpipers made up the majority of the Mid Bay (orange), and Least Sandpipers were most abundant in the Back Bay (green). Marbled Godwit photo courtesy of Mike Baird, all others courtesy of Marlin Harms.

Since 2010, Morro Bay’s survey results have been part of a broader study called the Pacific Flyway Shorebird Survey (PFSS), which partners with the Migratory Shorebird Project (MSP) to monitor shorebird populations across the Pacific Flyway from Chile to Canada. By monitoring shorebirds at their wintering areas in thirteen countries each year, this collaborative project generates species-level population trends for the Pacific Flyway to guide management and conservation efforts.

After steadily declining for years, Morro Bay shorebird abundance significantly increased in November 2024. For now, it is too early to tell whether this is a temporary change or an indication of recovery. Shorebirds from other areas can become temporarily displaced due to wildfire smoke, predators, and human disturbance. The displaced birds then contribute to short-term population increases in nearby areas. Future surveys will be instrumental in determining if this population increase is sustained in Morro Bay and whether trends are similar across the Pacific Flyway.