The phrase "are observed in a number of" is correct and usable in written English.
It can be used when discussing findings, trends, or phenomena that have been noted or recorded in various instances or studies.
Example: "Certain behavioral patterns are observed in a number of species during mating season."
Alternatives: "are noted in several" or "can be found in various".
Transoceanic migrations (greater than 1,000 kilometres) are observed in a number of marine vertebrates, and these movements often relate to requirements of feeding and reproduction.
New frequencies are observed in a number of cases, and their distribution gives information about possible causes for impedance spectrum distortion, eg about a poor linearity and/or instability of the electrode interphase during the measurement.
Aberrant DNA methylation and gene expression are observed in a number of conditions and diseases, including cancer, neuro-psychiatric disorders, and autoimmunity.
Higher TBHg levels are observed in a number of regions – e.g., Southeast Asia, the Amazon Basin, and the Arctic [ 3] – where HBV is also endemic [ 62, 63].
Compulsive behaviors (including perseveration) and impulsive behaviors are observed in a number of psychiatric conditions, including substance misuse and gambling disorders (Álvarez-Moya et al., 2009; Andersen & Teicher, 2009; de Ruiter et al., 2009; Lovallo, 2013).
With regard to menstrual cycle effects; for example, cyclical changes are observed in a number of different female reproductive hormones, and these changes influence a broad range of cognitive, emotional, and sensory processes (Dreher et al. 2007; Farage et al. 2008; Guillermo et al. 2010).
Since then, imprinting has been observed in a number of bird species including geese, ducks and, of course, cranes.
This phenomenon was observed in a number of mammalian species.
The massive blue stars were observed in a number of young and very bright galaxies, including one dubbed CR7--a nod to the Portuguese soccer player Cristiano Ronaldo.
Enhanced binding on GMPCPP microtubules was observed in a number of different conditions.
Emx2OS was observed in a number of CNS structures expressing also Emx2.
