Movement patterns of Peruvian Boobies off Isla Lobos de Afuera 2007

Carlos B. Zavalaga

GPS loggers and time-depth recorders were used to characterize the foraging behavior of the sexually dimorphic Peruvian booby Sula variegata on 2 islands in northern Peru. We evaluated whether (1) its foraging behavior differed from tropical boobies and temperate gannets (the Peruvian boobies feed in areas of enhanced productivity and high fish density), and (2) females and males exploited different foraging habitats as a consequence of size dimorphism. Birds foraged only during daylight hours, 1 to 3 times a day, in trips of short duration (median = 1.8 h). Overall, 92% of the total foraging time was spent flying. They fed exclusively on anchovetas Engraulis ringens, which were captured in shallow dives (median = 2.5 m, max = 8.8 m) with a dive median rate of 11 dives h–1 (max = 37 dives h–1). The median foraging range was 25 km (max = 68 km), whereas the median total distance traveled was 69 km (max = 179 km). Foraging site fidelity was high, and the orientation of foraging flights in any given day was similar among birds that departed at the same time. There were no sex-specific differences in 13 of 15 foraging variables; however, females dived slightly deeper and spent a larger proportion of time sitting on the water. We speculate that (1) the foraging behavior of Peruvian boobies contrasts with that of their tropical and temperate relatives as a result of the proximity and predictability of food sources, elevated energetic demands of the brood (up to 4 chicks) and
high prey encounter rate in the Peruvian upwelling system, and (2) the lack of spatial segregation between sexes may be related to the attraction of birds to feeding aggregations that are formed in the vicinity of the colonies. Once the foraging patches are localized, females dive deeper because of passive mechanisms associated with a heavier mass.

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Due to incorrect date/time or coordinates, the following records in the original data sheets were removed:
Bird ID 507
11:15:46, 3/8/2000, -80.821548, -7.104937
11:15:49, 13/08/2019, -80.8215, -7.105124
11:15:50, 13/08/2019, -80.821498, -7.105203
11:18:07, 13/08/2019, -80.815599, -7.10751
11:18:08, 13/08/2019, -80.815574, -7.107587
16:00:11, 5/1/2018, -80.779896, -7.11839
16:58:54, 5/4/2025, -80.760566, -167.071
16:09:57, 5/4/2025, -80.75794, -7.110085

Bird ID: 509
10:18:25, 13/08/2019, -80.693316, -7.032193
10:18:26, 13/08/2019, -80.693354, -7.032029

Bird ID: 530
12:25:10, 15/08/2019, -80.844323, -7.027227
12:25:11, 15/08/2019, -80.844369, -7.027112

Overview

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Attributes in dataset

Attribute (table column)	Description
oid	Unique ID number (generated by OBIS-SEAMAP)
bird_id	Bird ID
obs_time	Time of observation in UTC
obs_date	Date of observation
speed	Speed in km/h
longitude	Longitude in decimal degrees
latitude	Latitude in decimal degrees
sp_obs	Species name recorded
sp_tsn	Taxonomic Serial Number added by OBIS-SEAMAP
obs_count	Number of animals (always 1; added by OBIS-SEAMAP)
sex	Sex
age_class	Age (always Adult)
weight	Weight in grams
geom	Geometry field added by OBIS-SEAMAP