Diet of Double-crested Cormorants in NY Harbor, 2010 update

1. Diet of Double-crested Cormorants in NY Harbor, 2010 update Colin Grubel, CUNY Graduate Center & Queens College John Waldman, Queens College

2. 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%) Colony comparisons

3. 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 commersonii Crustaceans Sand shrimp, Crangon septemspinosa South Brother Species

4. 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 Swinburne Species

5. 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

6. Investigations into the Factors Affecting Pellet Production

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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 Morphologies

14. Otolith Morphology 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 • Shape important: Compact otoliths (Croaker, Scad, Pinfish) survived in higher proportions than delicate ones • Importance of size indeterminate. More research needed

15. 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

16. 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

17. 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