Look Out for Amorous Alligator Lizards

Spring is mating season for alligator lizards. From Baja California to British Columbia, we need your help to study their mating behavior.

Alligator lizard coitus 2021 by iNat user James

Above Image: A pair of mating southern alligator lizards observed by Jacob, Oscar (age 5), and Mae (age 4)  https://www.inaturalist.org/observations/73385631 in their front yard in the Valley Village neighborhood of Los Angeles on April 7, 2021. The male is biting the female’s head and neck region; this is termed the bite hold. Pairs may stay in the bite hold for several days even though mating only takes a small portion of this time. photo: Jacob 


Within the ranges of these two alligator lizard species are a handful of major museums, hundreds of universities, and thousands of biologists, so you might think we must know everything there is to know about these relatively common lizards. Unfortunately, like most other species on this planet, we still have a huge amount to learn about the basic natural history of alligator lizards. 

In 2015, we realized that we could use crowdsourcing as a way to study mating behavior. At that time, in the entirety of the scientific literature, there were only four dates reported for when southern alligator lizards had been observed breeding. We knew we could get more observations through community science, by crowdsourcing the study of this rarely documented behavior. We started asking people to send us photos and videos of mating pairs. We have now accumulated over 700 observations of mating southern alligator lizards, and over 100 observations of northern alligator lizards (as of February 2023). We are pretty sure that through community science, we have generated the largest dataset ever on lizard mating. This result demonstrates the incredible value of community science for studying rarely observed natural history events.

Madeleine Claire Doney  https://www.inaturalist.org/observations/73466001 found this pair of northern alligator lizards at Point Lobos State Natural Reserve in Carmel, California on April 6, 2021. This pair is in a bite hold, but they are not mating.   
photo: Madeleine Claire Doney


1. Wet years are the big breeding years.
The 2015, 2016, and 2018 mating seasons followed below-average rain seasons, and we received 32–35 observations of southern alligator lizards in the mating position (i.e., the bite hold, shown in the above images). But, following the wetter 2017, 2019, 2020, and 2022 winters, we received nearly three times as many observations! In 2020 and 2022, Southern California experienced very high rainfall in December and then very little rain in January and February, but we still received a large number of observations. This suggests that the lizards are responding not just to rainfall, but to early-season rainfall. Good December rains yield springs with lots of lizard mating activity. 

2. Weather has a big impact on mating activity.
Cooler and wetter weather can shut down mating activity until conditions improve. For example, in 2015, most of the mating activity in Los Angeles, Orange, and San Diego Counties took place between March 11 and April 17, but we received no reports for two week-long periods during which large storms swept through the region. 

3. Lizards can stay paired up for over two days!
The actual act of mating likely takes place shortly after the lizards pair up. However, the male maintains the bite hold for a long time. This is most likely a type of “mate guarding”, in which the male is trying to make sure that no rival males try to mate with the female (but we still have more research to do before we are positive this is what’s happening). But how long might a male maintain the bite hold? We now have four reports of pairs together over 48 hours, with the current record being a pair that were in a bite hold for at least 54 hours in an Orange County, CA backyard in March 2021. 

Cheryl Peach https://www.inaturalist.org/observations/73396823 observed this pair of southern alligator lizards in a bite hold in her Escondido yard on March 23, 2021. Note that this pair is in a bite hold, but they are not mating.
photo: Cheryl Peach

What to look for?
During mating season, males search out females. The male bites the female on her neck or head and may hold her this way for several days. Early in the encounter, the two may engage in a bit of a wrestling match (if you see this, please try to get videos). Sometimes, a second male shows up and we get even more interesting observations! About 9 percent of all observations in our dataset have two males and a female. 

When to look?
Because we have accumulated so many observations, we now know that the southern alligator lizard mating season can start as early as early February in the southern part of the range and continues into early June in the northern part of the range and at higher elevations. In Southern California, most of the breeding activity is between mid March and late April. This year, the season seems to be delayed, and mating pairs should be found in Southern California through early May. For the northern alligator lizard, breeding should occur from early April through mid-June.

Where to look?
Because we have accumulated so many observations, we now know that the southern alligator lizard mating season can start as early as early February in the southern part of the range and continues into early June in the northern part of the range and at higher elevations. In Southern California, most of the breeding activity is between mid-March and late April. In dry years, mating activity starts earlier, but following better rain seasons, mating activity usually begins in mid to late March.

For the northern alligator lizard, we don’t see mating activity in the south-to-north and low-to-high elevation patterns that we see in the southern alligator lizard. Northern alligator lizards can be breeding on the same day in Santa Cruz, CA, and on Vancouver Island, British Columbia. Pairs are most commonly found between early April and early June.

How to document? Take photos!
If the pair is wrestling, or otherwise being active, please take a video as well. We are especially interested in how long pairs remain in the mating hold, so please check back every few hours and search for the pair in the general area. If you find them again, please take a photo each time you encounter them so that we can assess whether they are mating, or in the bite hold, but not mating. 

If you see courting or mating alligator lizards, please take photos and ideally also a video if they are being active. Then upload these to iNaturalist if you are already an iNaturalist user or send them to us at the Natural History Museum by emailing the photo to nature@nhm.org. If you have photos from previous years, please submit those as well. We have received observations that date all the way back to 2003.

Danna Santos https://www.inaturalist.org/observations/73464347 observed this mating pair of southern alligator lizards in San Diego on April 4, 2021. This pair was found in a backyard in a residential neighborhood, highlighting that interesting nature observations can be made anywhere, as long as people choose to observe.
photo: Danna Santos