Evidence for Prey Species Spininess as a Factor Affecting Pellet Production

1
Evidence for Prey Species Spininess as a Factor
Affecting Pellet Production In Double-crested
Cormorants, Phalacrocorax auritus Colin Grubel,
CUNY Graduate Center Queens College Advisor
John Waldman, Queens College

• Introduction
• Double-crested Cormorants are communally nesting
  waterbirds that may threaten local fish resources
• Diet studies are an important part of management
• 3 main ways to study
• Direct stomach analysis
• Boli (regurgitated, partially digested food
  items)
• Pellets (contain bones, scales, otoliths and
  other indigestible items, contained in a mucous
  coat and regurgitated by the birds)
• Otoliths are akin to ear bones of fish
• Useful for identifying species
• Pellet analysis most popular
• Species not represented equally between pellets
  and boli
• Good evidence of biases but no evidence as to
  exactly what is causing them

• Field Work
• Methods
• Samples collected from colonies on three islands
  in New York Harbor during the chick-rearing
  season of 2008
• South Brother, Swinburne, Hoffman Islands
• Collected 434 boli 88 pellets
• Items identified in lab
• Results
• 402 boli contents identified
• 249 food items identified in pellets
• 35 species
• 32 species indentified in boli
• 21 species identified in pellets
• 52 of fish identified in bolus samples were
  spiny, 48 were nonspiny
• 95 of fish identified in pellets were spiny, 5
  were non-spiny

Searobins, Prionotus sp. (spiny fins) P in boli
10 P in pellets 26
Herrings, Clupeid sp. (soft rayed fins) P in
boli 8 P in pellets 4
Differences in species proportions between
pellets and boli. Columns indicate the
difference in relative frequencies of fish
species found in pellets versus their relative
frequencies in the boli . The non-spiny species
listed are oyster toadfish and the clupeid spp.

• Objective
• Determine whether fish with spines in their fins
  are better represented in pellets than fish
  without spine in their fins

• Conclusions
• Prey species morphology plays a part in pellet
  formation
• Species with spiny fins better represented in
  pellets
• Pellets produced more frequently in birds feeding
  on species with spiny fins
• Mechanism unknown, but the fact that mucous
  production is higher for pellets produced after
  ingestion of spiny species hints that the mucous
  may have a protective function
• Other aspects of morphology cant be ruled out
• Management decisions for cormorant populations
  based on diet need to take into account the
  effect of prey morphology on pellet production
  and any biases that may cause
• Where possible, use of pellets in diet assessment
  should be avoided

Otoliths per Pellet the number of otoliths found
in pellets. Note that pellets resulting from a
diet of pinfish contained on average more
otoliths and contained otoliths more frequently,
than those produced by a diet of scaled herring,
and that
Scenes from the research A. cormorants nesting
on a rooftop on Swinburne Island in NY Harbor, B.
a Suncoast Seabird Sanctuary employee preparing
to feed the birds in the feeding trial, and C. a
cormorant swallowing an Atlantic thread herring
during the feeding trial, D. black seabass,
Centropritis striata, otolith being extracted
from a pellet.

• Feeding Trial
• Methods
• Conducted feeding trial at Suncoast Seabird
• Sanctuary in Indian Shores, FL
• Two species of fish used
• Pinfish, Lagodon rhomboides spiny fins
• Scaled herring, Herengula clupeola soft-rayed
  fins
• Two groups of 5 birds, each group fed diet of
  entirely one species of fish for one week, then
  switched to second species
• Collected pellets dissected in lab (work ongoing)
• Bones, mucous and surviving flesh separated and
  weighed
• Otoliths identified and counted
• Results (preliminary)
• Birds produced pellets more frequently when fed
  pinfish, the spiny-finned species difference not
  significant
• Pinfish otoliths better represented in pellets
  than those from scaled herring

• Future Research
• Future research will involve more field work and
  feeding trials aimed at uncovering the effects
  of otolith morphology, percent bone mass and size
  of prey species

Pellet contents distribution of masses for
pellet contents, divided Into type (hard content
bones, otoliths, scales etc. and mucous), and
species represented. Mucous weights may be low
across all Samples due to degradation in the
preparation process

• Special Thanks to
• Queens College, CUNY Graduate Center, The
  Huckleberry Indians, The Jamaica Bay Institute,
  Scott Barras- US Department of Agriculture, Andy
  Bernick, Richard Chipman - US Department of
  Agriculture, Mary Cool, Tony Dilernia -
  Kingsborough Community College, Theresa Duhon,
  Mike Eddy - Kingsborough Community College, Kathy
  Garofalo - National Parks Service, John Haley,
  Kate Ruskin - NJ Audubon, Sean Seagriff -
  National Parks Service, Tom Veltre - The Really
  Interesting Picture Company, John Waldman -
  Queens College, Chip Weseloh - Canadian Wildlife
  Service
• NYC Audubon Elizabeth Craig, Susan Elbin, Yigal
  Gelb, Alexis Marie Mychajliw
• NYC Parks Service Mike Feller, David Kunstler,
  Nate McVay, Ellen Pehek, Susan Stanley, Alex
  Summers
• Suncoast Seabird Sanctuary Barbara Suto,
  Melanie Boucher, Rudy Jara, Scott Patterson
• Finally, thanks to Liz Vreeland of Suncoast
  Seabird Sanctuary, who caught all the herring for
  the feeding trial
• This research has been funded in part by
• CCNY Research Associations PEER Grant
• The Hudson River Foundations Polgar Fellowship
• NYS DEC
• iLANDs iLAB Dance Fellowship.

Pinfish, Lagodon rhomboides (Spiny fins)
Scaled herring, Herengula clupeola (Soft rayed
fins)