| Bird watcher's accessory | 28 |
| Aid in judging distances | 24 |
| Consisting of two terms | 23 |
| Certain theorem in math | 23 |
| Asimov, per his doctorate | 25 |
| Marketer's accumulation | 27 |
| Capable of being decomposed | 27 |
| Renewable fuel on some farms | 28 |
| Result of some fermentation | 27 |
| Hypothetical protein molecule | 29 |
| Hypothetical cell unit | 22 |
| Like Ernst Haeckel's law | 28 |
| Controversial engineering | 25 |
| Jet lag monitor, in a way | 25 |
| Natural timekeeper, of a sort | 29 |
| Controller of life cycles | 25 |
| Watson and Crick, for two | 25 |
| What John Scopes taught | 23 |
| Renewable energy source | 23 |
| Plant material used for fuel | 28 |
| Organic matter used for fuel | 28 |
| Living matter in total | 23 |
| Ecological communities | 22 |
| Some complex communities | 24 |
| Carbon dioxide measurer | 23 |
| Sight-restoring innovations | 27 |
| Medical diagnostic test | 23 |
| Invasive medical procedure | 26 |
| Skin care brand with strips | 27 |
| Modern-day medical diagnostic | 29 |
| Life on earth, collectively | 27 |
| Experiments on organisms | 24 |
| Certain drugs, for short | 24 |
| Vitamin in yeast and liver | 26 |
| One of the B-complex vitamins | 29 |
| Organisms sharing a trait | 25 |
| Genetically related organisms | 29 |
| Like humans and ostriches | 25 |
| Having two feet, not four | 25 |
| Sopwith Camel, for one | 22 |
| Wingwalker's vehicle | 24 |
| Red Baron's transport | 25 |
| It stands on its own two feet | 29 |
| Mortars' supporters | 23 |
| Three-term Indiana senator | 26 |
| Ex-Senator from Indiana | 23 |
| Trees with papery bark | 22 |
| Trees used in furniture | 23 |
| Robins' rest stops | 22 |
| Audubon Society member | 22 |
| Tourists with spotting scopes | 29 |
| Avid ones keep Life Lists | 25 |
| Audubon Society members | 23 |
| Sparrow avoids a snare? | 23 |
| Horus, to ancient Egyptians | 27 |
| Shelters in some backyards | 26 |
| Reasons for some low scores | 27 |
| Observation of cardinals, say | 29 |
| Words for a sure thing | 22 |
| 1962 Burt Lancaster film? | 25 |
| What might fly up your nose | 27 |
| Colorful, ornate flower | 23 |
| Cockatoo in the White House? | 28 |
| "Sweet Hostage" | 25 |
| Goldie Hawn film of '90 | 27 |
| Facts of life in the park? | 26 |
| Ornithophiles' purchases | 28 |
| Big name in frozen food | 23 |
| Seen from above, as a view | 26 |
| Frozen food pioneer Clarence | 28 |
| Book by an aviculturist? | 24 |
| Chinese soup ingredients | 24 |
| They have common interests | 26 |
| The company one keeps, often | 28 |
| Symbols of togetherness | 23 |
| Proverbial flying companions? | 29 |
| People with the same tastes | 27 |
| People with similar traits | 26 |
| People with common interests | 28 |
| It may be heard in an aviary | 28 |
| Nightingale's serenade | 26 |
| 1984 Matthew Modine movie | 25 |
| 1984 Matthew Modine film | 24 |
| 1984 film with Matthew Modine | 29 |
| Vessel with two tiers of oars | 29 |
| Hellenistic-era galley | 22 |
| Galley with two banks of oars | 29 |
| Phoenician double-deckers | 25 |
| Ancient double-deckers | 22 |
| Hindu's cheap cigarette | 27 |
| Cheap cigarette of India | 24 |
| Spin after logging on? | 22 |
| Play a loggers' game | 24 |
| Competitive lumberjack | 22 |
| Black Sabbath origin locale | 27 |
| Author of Now is the Time | 26 |
| Ballpoint pen inventor | 22 |
| Ballpoint pen inventor Lazlo | 28 |
| Ball point pen inventor | 23 |
| Any pen, in British parlance | 28 |