Catwalks hang over a section of the newly constructed eastern span of the San Francisco-Oakland Bay Bridge during a media tour of the self-anchored suspension span tower on August 29, 2011 in Oakland, California. Contruction crews have erected twelve foot wide catwalks that connect to the San Francisco-Oakland Bay Bridge self-anchored suspension span's tower and crews will begin to lay the nearly one mile of main cable beginning in early 2012. The bridge has been under constrution since 2002 with an estimated price tag of $6.3 billion and will have the world's tallest Self-Anchored Suspension (SAS) tower once completed. (Photo by Justin Sullivan/Getty Images)

Young revelers take part in a parade called "La Calabiuza" on November 1, 2015, on the eve of the Day of the Dead in Tonacatepeque, 20 kms (13 miles) north of San Salvador. During the celebration, the residents of Tonacatepeque, originally an indigenous community, recall the characters from the mythology of Cuscatlan – pre-Columbian west and central regions of El Salvador – and their dead relatives. (Photo by Marvin Recinos/AFP Photo)

Comandos de Salvamento rescuers Maria Martinez (L) and Ana Chichilla attend to a wounded homeless man in San Salvador, El Salvador July 16, 2016. The man was attacked with a machete by suspected gang members. In 2015, El Salvador registered a record 103 homicides per 100,000 habitants, making it one of the most dangerous countries in the world outside a war zone. But for many young people who have few chances to distance themselves from rivalries between so-called maras in their schools and neighbourhoods, a civil-society organisation called the Comandos de Salvamento, or Rescue Corps, has been a refuge. (Photo by Jose Cabezas/Reuters)

Pfc. Esmeralda Calderon stands and salutes the flag on the 15th green during the first round of the LPGA golf tournament at Kingsmill Resort and Golf Course in Williamsburg, Va., Thursday May 23, 2019. Pfc. Calderon, from San Antonio, Texas, is a Marine assigned to Naval Weapons Station Yorktown. (Photo by John Sudbrink/The Daily Press via AP Photo)

Ocean Beach after a rain storm in San Francisco, California, US, on Thursday, January 5, 2023. A powerful storm with hurricane-force gusts has begun to wind down after ripping across California, leaving behind power outages, flood threats and road closures just hours before another drenching is set to wash over the state. (Photo by Shelby Knowles/Bloomberg)

A pedestrian walks by an Apple Store following an announcement that Apple has become the world's most valuable brand on May 9, 2011 in San Francisco, California. In a report released by London based Millward Brown, Apple Inc. has surpassed Google to claim the top spot in a global ranking of brand value this year with an estimated value of more than $153 billion up 84 percent from last year. (Photo by Justin Sullivan/Getty Images)

Apple CEO Steve Jobs delivers the keynote address at the 2011 Apple World Wide Developers Conference at the Moscone Center on June 6, 2011 in San Francisco, California. Apple CEO Steve Jobs returned from sick leave to introduce Apple's new iCloud storage system and the next versions of Apple's iOS and Mac OSX. (Photo by Justin Sullivan/Getty Images)

Sharon Beals is a San Francisco based photographer who has photographed nest and eggs specimens collected over the last two centuries at The California Academy of Sciences, The Museum of Vertebrate Zoology, and The Western Foundation of Vertebrate Zoology. While few nests are collected today, these nests and eggs are used for research, providing important information about their builder’s habitats, DNA, diseases and other survival issues.