Mrs. (Sarah) Trimmer's first principle in respect to the treatment of birds and other animals was Christian mercy. It would be tempting to assign her to the "sentimental" camp in the history of bird protection if only she hadn't herself put so many bounds around the proper application of such mercy. To begin, it was sinful to feed to animals food fit for human consumption--poor and destitute humans were more worthy recipients for leftovers. At the same time, it was also sinful to throw away crumbs that had fallen to the floor--those should go to the birds. While cruelty to animals was morally abhorrent, so was intemperate love of one's pets. Human needs always came first, but humans needed to empathize as much as possible with inferior beings (whether work horses or house flies).
Trimmer dramatized these principles in a pair of books, An Easy Introduction to the Knowledge of Nature, and Reading the Holy Scriptures, Adapted to the Capacities of Children (1770) and Fabulous Histories Designed for the Instruction of Children Respecting their Treatment of Animals [AKA The History of the Robins] (1786). In the first, Trimmer used dialogue between a wise mother and her two children to convey the wonder of God's "book of nature." In the second, Trimmer narrated the intersecting stories of a family of (European) robins and two young human children (with the wise mother character never far away). The novelty of Fabulous Histories was the depiction of the robins as thinking and speaking beings, a bit of poetic license that Trimmer took pains to try and disenchant.
With respect to attitudes toward birdlife, An Easy Introduction displays beliefs consistent with those of Joseph Addison and Richard Steele earlier in the century. The mother character repeats Addison's line about blackbirds and cherries almost verbatim and reveals that she would sometimes buy captive larks at the marketplace in order to release them in the wild. Ultimately, however, birds lacked "souls" (which coincided, for Trimmer, with cognition and the ability to speak) and thus were inherently inferior to humans.
By the time she wrote Fabulous Histories, however, her thoughts about birds and speech seem to have shifted a little, which made the need for mercy even more pressing. Here's the wise mother counseling her daughter about trying to raise wild chicks in the home:
I cannot think you have any cruelty in your nature, but perhaps you have accustomed yourself to consider birds only as playthings, without sense of feeling. To me, who am a great admirer of the beautiful littler creatures, they appear in a very different light; and I have been an attentive observer of them I assure you. Though they have not the gift of speech like us, all kinds of birds have particular notes which answer in some measure the purpose of words among them, by means of which they can call to their young ones, express their love of them, their fears for their safety, their anger towards those who would hurt them, etc. from which we may infer that it is cruel to rob birds of their young, deprive them of their liberty, or exclude them from the blessings suited to their natures, for which it is impossible for us to give them an equivalent.
Besides, these creatures, insignificant as they appear in your estimation, were made by God as well as you. Have you not read in the Testament, my dear, that our Saviour said, "Blessed are the merciful, for they shall obtain mercy?"
I am of the opinion... that it would be a good way to accustom one's self, before one kills anything, to change situations with it in imagination, and to suppose how we feel were we bees, or ants, or birds, or kittens.
In addition to offering a specific argument (Christian mercy) for the protection of birds, Fabulous Histories is also a useful guide to late 18th century attitudes toward certain bird species. As we've seen before, robins ("Babes in the Woods") and swallows (insect-eaters) got a free pass, while bullying, stealing house sparrows deserved their persecution. Trimmer used other species to convey certain moral points linked to their natural behavior. Chattering magpies, for example, were foolish--always talking, never listening, while cuckoos were lazy, house-stealing foreigners. Trimmer even imported a mockingbird character (with an appropriate footnote indicating its American origin) to show how children how ridicule is funny until directed at one's self.