haven't been able to find a source for this photo that isn't tumblr or facebook...
If these ARE German, then they're probably a fad brought over from somewhere else. Looking into it a bit, maybe they're copied / inspired by the mermaid whistle / rattles from Spain or belled amulet rattles from Italy?
Anyway, the facebook version for this specific pic says:
"Hunting Whistles - also in the form of a Stylized Siren, 16th century. Silver and gold.
Hunting whistles, as well as falconry whistles from the medieval and Tudor period are very rare, with only four other examples in silver listed on the Portable Antiquities Scheme, whilst another three are in the Museum of London collection.
A beautiful gold hawking whistle that was given by Henry VIII to Anne Boleyn can be seen in the Victoria & Albert Museum."
One of the items in this picture (second down on the right) has a very similar look-a-like on manuelohen dot com which says:
"Amulet, Museu Maritim de Barcelona, Barcelona, Spain
Amulet, a bell, rattle and whistle in the form of a mermaid, silver, 18th century, in the Museu Maritim de Barcelona, or Barcelona Maritime Museum, housed in the former medieval royal shipyards and arsenals at Drassanes, Barcelona, Catalonia, Spain. The museum houses exhibits on the maritime history of Catalonia, including many ships and boats built in the shipyards of Barcelona. Picture by Manuel Cohen."
Mermaid whistles with bells maybe seem to be A Thing.
As with this one, which also looks kinda like on in the original pic, second down on the left, at Autioneum, which lists it as:
18TH CENTURY SPANISH SILVER GILT FIGURAL MERMAID WHISTLE RATTLE AMULET
An 18th century Spanish silver gilt figural whistle rattle. The rattle in the form of a siren mermaid, mirror in hand and holding a cylindrical whistle aloft, strung with bells and foliates upon fancy link chain. The chains united by a figural surmount having large fashioned bale. Unmarked, tests indicate silver. Measures approx 16cms drop x 7cms width. AF the rattle retains most original gilding, a few bells have been lost over time.
There's also this whistle / rattle / amulet in a similar style that's both listed as Sold on antiquestore dot art AND listed as for sail on graysantiques dot com both of which describe it as:
"A silver gilt mermaid rattle and whistle.
North European, probably Frisia, mid 18th century.
Measures 11.2 x 7.5cm, excluding chain but including bells.
Amulets in the form of a mermaid have been used since the 17th century. The noise of the bells hanging along the lower edge would help to frighten off any evil spirits. In medieval France the mermaid also merged with the symbolism of motherhood."
For museum sources, there's this horse rattle from Italy, as seen on clevelandart dot org, that's got the same basic style, silver with the chain suspension and hanging bells, which lists it as:
Rattle
1700s
Italy, Sicily, 18th century
silver
Overall: 23.5 cm (9 1/4 in.); Average: 7.7 x 7 cm (3 1/16 x 2 3/4 in.)
The Mary Spedding Milliken Memorial Collection, Gift of William Mathewson Milliken 1947.275
've got no study in any of this, but if the original pic IS of some "German Hunting Whistles", then I'm very sad that the one hunting museum in Munich I've seen didn't have any :(
(it did have a really nice collection of swords, horns, and stuffed Wolpertingers tho)