Diet of Double-crested Cormorants in NY Harbor,

2010 update

Colin Grubel, CUNY Graduate Center & Queens College

John Waldman, Queens College

Colony comparisons

South Brother 4 collection trips 83 items

identified 15 sp. fish, 1

crustacean Most common

sp: Hogchokers (24%) & goldfish (22%)

Swinburne 2 collection trips 72 items

identified 18 sp. fish, 1

crustacean Most common

sp: spotted hakes (29%)

South Brother Species American eel, Anguilla

rostrata Brown bullhead,

Amerius nebulosus Cunner, Tautogolabrus

adspersus Goldfish, Carassius

auratus Hake, spotted,

Urophycis regius Herring, blueback,

Alosa aestivalis Hogchoker, Trinectes

Maculatus Menhaden, Brevoortia

tyrannus

Northern pipefish, Syngnathus fucus Oyster toadfish, Opsanus tau Sculpin sp. Striped cusk eel, Ophidion marginatum Tautog, Tautoga onitis White perch, Morone americana White sucker, Catostomus commersoniiCrustaceans Sand shrimp, Crangon septemspinosa

Swinburne Species American eel, Anguilla rostrata Bay anchovy, Anchoa mitchilli Black Seabass, Centropristis striata Cunner, Tautogolabrus adspersus Flounder, summer, Paralichthus dentatus Flounder, winter, Pseudopleuronectes americanus Grubby sculpin, Myoxocephalus aenaeus Hake, red, Urophycis chuss Hake, spotted, Urophycis regius Herring, Atlantic thread, Opisthonema oglinum Herring, blueback, Alosa aestivalis Hogchoker, Trinectes maculatus Menhaden, Brevoortia, tyrannus

Mummichog, Fundulus heteroclitus Northern pipefish, Syngnathus fucus Oyster toadfish, Opsanus tau Rock gunnel, Pholis gunnellus Sculpin, grubby, Myoxocephalus aenaeus Sculpin, shorthorn, Myoxocephalus scorpius Scup, Stenotomus chrysops Searobin, northern, Prionotus carolinus Searobin, striped, Prionotus evolans Tautog, Tautoga onitis

Crustaceans Blue crab, Callinectes maculatus

Conclusions

Swinburne results from trips close together Can’t be easily extrapolated to rest of

season No new species found Rarity of formerly popular species (scup,

black seabass) and unusual popularity of hakes may be due to

South Brother surveyed more thoroughly than previous years 1 new species (white sucker) Bluegills, Lepomis macrochirus, and

Pumpkinseeds, Lepomis gibbosus, usually common, not found

Investigations into the Factors

Affecting Pellet Production

Introduction Diet studies are an important part of

management Boli & pellets most common methods of

diet assessment Boli (regurgitated, partially digested food

items) Pellets (made up of 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 – highly species specific

Species not represented equally between pellets and boli

Good evidence of biases but no evidence as to exactly what is causing them

Feeding Trials Prey spininess Otolith

morphology Prey size

• Two enclosures, housing 3 birds• Floors lined with Astroturf to prevent sand

accumulation• Colored glass beads inserted into fish being fed out -

help quantify the time each pellet has taken to form

Preliminary Trial – effect of captivity

Two groups of 3 birds: long term residents – cripples & new residents rehabs Each fed equal amounts of pinfish once

a day for 7 days Results: Over the course of the week

the crippled bird produced only 9 pellets and the rehab birds produced 14 The reason for this difference is

unknown

Prey Spininess Hypothesized that spines present on

some species of fish may irritate the gut Would speed up pellet production Less time in gut would mean more

otoliths surviving in pellet

Previous fieldwork indicated spininess as a possible factor affecting pellet production 52% of fish identified in bolus samples

were spiny, 48% were non–spiny 95% of fish identified in pellets were spiny,

5% were non-spiny

Spininess

Birds fed unaltered pinfish for one week and pinfish with spines removed for a second week

Removal of spines led to a small decrease in the number of pellets regurgitated

Also led to an increase in the average number of days it took pellets to form

Data needs to be explored further

Otolith Morphology Not all otoliths are

equally likely to occur in pellets

Possible reasons include size and shape

Otoliths of different sizes and shapes manually inserted into false pilchard being fed out

Otolith Morphologies Compact

otoliths Croaker

Scad

Pinfish

goldfish Fragile otoliths

Threadfin herring

False pilchard

Otoliths by size Croaker (avg length

10.12µ)

Scad (6.94µ)

Pinfish (3.7µ) Large threadfin

(3.57µ) Small threadfin &

false pilchard (2.53µ)

Goldfish*

Otolith MorphologyOtolith Survival in Pellets

0

5

10

15

20

25

croaker scad pinfish large threadfinherring

false pilchard &small threadfin

herring

Species

% recovered in pellets

Avg size (µ)

Shape important: Compact otoliths (Croaker, Scad, Pinfish) survived in higher proportions than delicate ones

Importance of size indeterminate. More research needed

Otolith Survival in pellets: % recovered refers to the proportion of otoliths from each species which survived to be recovered in pellets. Average size is the average length (µ) of otoliths of the different species

Fish Size Currently looking at the effects of prey

size Fish sized had been proposed to affect

the rate of pellet production Revisit effect of otolith size on survival in

pellets

Conclusions The timing of pellet production

may be affected my spininess of prey species but results inconclusive

Length of captivity appears to play a part as well, reason unknown Process may be different in wild

birds Otolith shape can affect the

likelyhood of surviving to be ejected and identified in a pellet

Otolith size may also be important but more research needed

Acknowledgments Special Thanks to: Queens College, CUNY Graduate Center, The

Jamaica Bay Institute, Andy Bernick, Mary Cool, Kathy Garofalo - National Parks Service, Kate Ruskin - NJ Audubon, John Waldman - Queens College, Chip Weseloh - Canadian Wildlife Service

NYC Audubon – Elizabeth Craig, Susan Elbin NYC Parks Service – Mike Feller, Nate McVay,

Ellen Pehek, Susan Stanley, Alex Summers Suncoast Seabird Sanctuary – Barbara Suto,

Scott Patterson, Melanie Boucher, Ryan Graham, Jessica Ann Greenert, Rudy Jara, Ingrid Lorm, Diana Machinski, Louis Pollicino

Finally, thanks to Liz Vreeland, volunteer of the Suncoast Seabird Sanctuary, who caught most of the pinfish for the feeding trials

This research has been funded in part by: CCNY Research Association’s PEER Grant The Hudson River Foundation’s Polgar and

Graduate Fellowships NYS DEC