I have a PDF copy of the paper below:

BIRD EGGSHELL IN DOMINICAN AMBER
2007. G. Poinar, Jr., et al. Paleontology 50 (6), 1381–1383.

Abstract: Here we report an eggshell in Dominican amber, representing
the first vertebrate egg in any amber deposit. The eggshell is
compared with present-day eggs of lizards, snails and birds. Based on
the surface structure and type of shell breakage, it appears that the
most likely candidate is a bird, and with that consideration, an avian
group that produces eggs similar to the fossil in shape, size and
colouration is the Trochilidae (hummingbirds). Several possible
explanations of how the fossil could be preserved in amber are
provided. If indeed a hummingbird was involved, this discovery would
represent the first New World record of a fossil trochilid.