Have cockatiels or Agapornis species parents crop milk as pigeons have?

I am afraid not.
Crop milk is a semi-solid, crumbly excretion high in fat and protein that some bird species feed to baby birds during the first days after hatching. It is a secretion from the crop of parent birds.
This crop milk is only found in pigeons and doves [Columbidae].
Flamingos [ Phoenicopteridae] and the male emperor penguin [Aptenodytes forsteri] are producing something similar but this is a secretion from the esophagus.
Cockatiels [Nymphicus hollandicus]or Agapornis species have neither.

Sources:

[1]
M. J. Gillespie e.a., ‘Histological and global gene expression analysis of the “lactating” pigeon crop’, BMC Genomics, vol. 12, nr. 1, p. 452, sep. 2011, doi: 10.1186/1471-2164-12-452.
[2]
D. E. Blockstein, ‘Crop Milk and Clutch Size in Mourning Doves’, The Wilson Bulletin, vol. 101, nr. 1, pp. 11–25, 1989.
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3 comments

    1. Hello,
      this is not an opinion I am afraid. These are facts, multiple times proven by research. There are several papers about this subject. I will add these sources to the post as well

      [1]M. J. Gillespie e.a., ‘Histological and global gene expression analysis of the “lactating” pigeon crop’, BMC Genomics, vol. 12, nr. 1, p. 452, sep. 2011, doi: 10.1186/1471-2164-12-452.
      [2]D. E. Blockstein, ‘Crop Milk and Clutch Size in Mourning Doves’, The Wilson Bulletin, vol. 101, nr. 1, pp. 11–25, 1989.

      I qoute from one of these papers:
      Both male and female pigeons (Columba livia) possess the ability to produce a complete nutrient substance, termed pigeon ‘milk’, for the nourishment of their young. Pigeons generally lay two eggs one day apart, which hatch 18 days after they are laid [1]. Two days before the first egg hatches, pigeon ‘milk’ begins to be produced in the crop of the parent birds. A similar substance is produced by flamingos [2] and male emperor penguins [3]. As in any other bird species, the normal function of the crop is as a food storage area located between the oesophagus and proventriculus where food is moistened before further break-down and digestion through the gastrointestinal tract [1]. During the process of pigeon ‘lactation’, a curd-like substance is regurgitated from the crop to the squab.

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