66 
that the bird is typically encountered flying away from the observer. The 
more extensive brown on the sides may be a good feature to look for. In 
light winds Tahiti Petrel hugs close to the water surface. 
Mottled Petrel # Obs. =7 
Pterodroma inexuectata 
The first mottled was seen on 28 March between Jarvis and Malden. 
Others were seen between Starbuck and Samoa in the Southern Grid, 5° HI, 
and north of the 12° area (29 April). 
Dark-rumped Petrel if Obs. 
Pterodroma phaeopygia 
Both sightings were south of Oahu in March (ll & 12). The same 
eastern tendency noted under Newell Shearwater may occur in this species,. 
The characteristic Pterodroma flight is the best criterion to separate 
birds from the similar Light-phase Wedge-tail, and, indeed, dark-rumps 
are more likely to be passed off as Juan Fernandez .‘Petrels. 
Pterodroma externa externa 
" " cervicalis 
. " " ssp.? 
Unidentified Large Pterodroma 
Total Large Pterodroma 
Pterodroma hypoleuca nigripennls 
" leucoptera 
" cooki 
Unidentified Small Pterodroma 
Total Small Pterodroma 
Unidentified Pterodroma sp. 
Total 
# 
Obs. 
= 60 
# 
Obs. 
» 1 
# 
Obs. 
= 84 
# 
Obs. 
- 2 5 
213 
# 
Obs. 
= 8 
# 
Obs. 
= 3 
# 
Obs. 
= 1 
# 
Obs. 
= 1+2 
# 
Obs. 
= 38 
295 
9 
The category "Large Pterodroma " includes almost only ?. externa and 
is typically employed in the field as an identification reliability 
measure. The white-necked form probably occurs more frequently than tne 
1 in 60 ratio suggested above but probably no greater than 1 in 10 to 1 5* 
Only one P. externa was recorded south of the equator. The peak concentra* 
tion noted in the 12° N. area is probably quite valid. Many birds (3b) 
were recorded from the 5° N..area, but the overall linear density is no^ 
exceedingly high. The April observations alone (see Graph 93) show a peak 
in the 5° N. section and a slight peak again in the 12° N. section. ^The 
overall picture for four months shows a regular increase from the Grid 
(2° N.) to the 12° N. area, including good numbers in the othervise barren 
region between 5° and 12° N. North of the 12° N. area a decrease is qu^^e 
evident. The temporal changes of birds are not altogether clear, in gen¬ 
eral, numbers have dropped somewhat since highs in late fall ana early 
winter of 1966 . My feeling is that there has been a general eastward 
movement. 
Identification problems continue to plague tne small. Pterocroma xorms. 
Very little can be said in general about the complex but I will contribute 
my intuitive feelings to further confuse the situation• 
