Frigatebird soars for weeks without landing

The orginal paper published 74 1 JULY 2016 • VOL 353 ISSUE 6294 sciencemag.org SCIENCE has a lot more information. For example, their observed L/D was 23.6-19.1 between 500-700 m, but 14.3-11.7 at higher altitudes.

I'm still trying to figure out how they stay aloft at night.

A Tasty Exerpt:
"However, birds regularly climbed up to 1000 to
2000 m, with a maximum of 4120 m (fig. S9). The
frequency of climbs at altitudes higher than 700 m
increased throughout the day to peak during the
first hours of night (fig. S10). Climbing to high
altitudes can be separated into a phase of slow
climb up to the base of the cumulus clouds at 600
to 700 m, followed by a more rapid climb to 1600 m
(Fig. 2D) or higher. This second phase of the ascent
is performed without flapping the wings (Fig. 2D);
i.e., in pure soaring flight and with climb rates
reaching 4 to 5 m s-1.

Ascent to high altitude can only take place inside
cumulus clouds, where updrafts reach 5 m s−1
at 2000 to 3000 m (fig. S11).
and are strong enough to provide such climb rates (15).
During the gliding phase made outside the clouds,
the minimum sink rate was 23.6 ± 19.1 m of ground
distance covered per meter lost between 500- to
700-m altitudes, compared to 14.3 ± 11.7 m at high-
er altitudes (F1,7 = 8.4, P = 0.045)."