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How do increasing daylight hours stimulate reproduction in frogs birds and mammals?

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Diagram comparing reproductive pathways: arrows show sexual reproduction forming a diploid zygote from oocyte and sperm, haploid parthenogenesis forming a haploid individual, and two types of diploid parthenogenesis-automixis and apomixis-both resulting in diploid individuals. Symbols indicate haploid and diploid stages. — Animal reproductive system The process of sexual reproduction and several forms of parthenogenesis.

Increasing daylight hours serve as a primary environmental cue for many vertebrates, signaling the onset of favorable conditions for reproduction. This process, known as photoperiodism, involves a complex interaction between the environment and the animal's endocrine system.123

The Mechanism of Stimulation

When an animal detects increased daylight, the signal is processed by the brain, which triggers the pituitary gland to release hormones called gonadotropins. These hormones travel through the bloodstream to the gonads, stimulating them to grow, mature, and produce gametes (eggs and sperm) as well as sex hormones like estrogen and testosterone.245

Birds: Light can reach the brain through the eyes or even the skull, stimulating cells that prompt the pituitary gland to initiate the reproductive cycle.5
Mammals: While some mammals rely on light to trigger ovulation, others use melatonin—a hormone produced by the pineal gland in response to darkness—as a biological clock to time their breeding seasons.46
Frogs: As vertebrates, amphibians also utilize hormonal pathways influenced by environmental cycles, and melatonin was historically identified through its ability to affect skin color in frogs.6

These responses ensure that reproduction occurs when environmental conditions, such as food availability, are most likely to support offspring.13