Sept, 1909 
151 
THE NESTING OF THE HEERMANN GULL 
By PINGREE I. OSBURN 
WITH TWO PHOTOS 
I N the spring of 1909, it was my privilege to be one of a party to make a^cruise 
down the west coast of Mexico in search of interesting forms of bird and animal 
life. The primary object of my trip was to discover, if possible, the nesting 
place of the Heermann Gull ( Laras heermanni ) . Every year these birds have 
migrated south in the spring and were generally supposed to breed somewhere in 
the Gulf of Lower California. After a sea voyage of over 1500 miles (from San 
Diego, California) they were located breeding on a remote rock off the coast of the 
State of Jalisco, Mexico, in about the parallel 18° N. 
Prior to the time of the visit of our party little or nothing was known of the 
habits of these birds in their breeding grounds, and the observations taken in this 
colony have brought to light many facts. 
NESTING GROUNDS OF THE HEERMANN GULP: ISLANDS OFF 
COAST OF JALISCO, MEXICO 
No Heermann Gulls were seen on the trip until found at their breeding 
grounds, nor w'ere any noted flying about at any distance from the nests on the 
rock, which would indicate that they do not wander away from their colony in the 
nesting time, as do the Western Gulls ( Lams occidentalis ) . When approaching a 
colony of Western Gulls its nearness is evidenced by occasional individuals sailing 
about for miles on all sides of their nesting grounds. Not so with Larus heermanni. 
They were not seen farther than one-half mile from the colony. Possibly this is 
one reason why their nesting grounds are easily overlookt. This fact was imprest 
upon me clearly while getting acquainted with the species in its native haunts. 
We were anchored two days near the nesting rock before the first bird was seen. 
My first glimpse of the birds was when an adult flew near enough to our 
schooner for identification, and I at once determined to make an effort to find more; 
for what was an adult doing in these waters at the hight of nesting time, April 10? 
The next morning (April 11)1 noted a few flying about over a low flat rock a 
little distance from our anchorage. It was here that I first found them breeding 
