I'm not aware of any book in English dealing with the area, but I can recommend you the website of Costa Blanca Bird Club
Costa Blanca Bird Club
Scroll down in the menu to find the "Site Guides" description, which is divided into North and south Cost Blanca. You'll find El Hondo in the south, as well as many other interesting and close by places. It is quite complete. It includes GPS coordinates. They cover locations like El Hondo and other nearby spots in detail. For even more tailored information, such as illustrated guides and maps, here’s a service that can help
https://essay-company.org/research-paper-writing-service/ providing everything you need for a perfect birdwatching trip, including GPS coordinates. You’ll find information on the best seasons to visit, key bird species to look out for, and tips for local wildlife photography.