David Gilmour has never again played Echoes live since Rick Wright (keyboards) died. He has always considered Echoes a "duet" both in singing & in the way the keyboards & guitar played off each other. He said "another guy could learn the keyboard part, but could never have the chemistry that I had with Rick". Their final performance before Rick's death always hits me...especially the last part ...it's so beautiful. https://www.youtube.com/watch?v=zrProK5R7ms
The squeaky sounds were discovered when Dave plugged ghis guitar into a certain pedal backwards. I guess they were pleased with the result and used it.
The seagull sound effect is achieved by David taking his Vox wah wah pedal and reversing the cord plugs. That is, the wah wah pedal's output to the amp is plugged straight from the guitar and the input is plugged into the amp. On his black strat he switches to the two bottom pickups and the tone knob is all the way off and the volume is turned all the way up. The guitar is then played through the tone knob turning up the tone creates the effect. Turning it back slowly gives it the laughing effect.
Note that at the very beginning of the song David is rubbing the strings of his guitar with a solid steel slide/tone bar in his right hand as he frets the strings with his left. That gives the guitar a violin kinda sound. Then at about the 2:40 mark in your video you see him switch out the tone bar for a steel slide on the finger of his left hand. Also, Rick at the very beginning is playing a grand piano that is mic'd through a Leslie speaker. There are three Leslies in that bank of speakers. They are the short brown cabinets behind Nick, David and Rick respectively. Rick then moves to what looks like his Hammond organ. Though he also played a Farfisa Compact Duo. At 19:47 between Rick's hands you can see the gold letters "compact duo".
This video is part of Adrian Maben's movie that came out in the mid 70s but it was filmed in the first week of October 1971.
There is a live version of Echoes from David Gilmour's 2006 "On an Island" solo tour. Rick Wright, Pink Floyd's keyboardist, joined him on that tour. Their last performance on that tour was in Gdansk, Poland and their performance of Echoes would be the very last time it will ever be performed live. Unbeknownst to David at the time, his good friend Richard was battling cancer and would succumb soon thereafter. So that performance, and the interaction between the too, is extremely poignant and emotional.
You should react to David Gilmour’s version of this from his live at Gdańsk show. It was the last time him and Rick Wright played it together before Rick died
I never get tired of listening to this unique universe, contained in a single reason: to take me to space. It's amazing to think about the possibility that we can sit back, play and be carried away by the sound.
I got to see them live in fall 1972 in Austin Tx. They played in a smaller rectangular hall and used a quad sound system so the music was always circling around us. Astronomie Domine, Set the Controls for the Heart of the Sun, Careful with that Axe Eugene were all played in full extended glory and the encore was the long version of Echos. To this day, 50 years later, that is still what I measure concerts by.